IMPACT TESTING

INSTITUTO POLITCNICO NACIONALESCUELA SUPERIOR DE INGENIERA MECNICA Y ELCTRICAUNIDAD CULHUACNIMPACT TESTINGDISEO DE ELEMENTOS MECNICOSPRESENTAN:CRDENAS ALVAREZ JULIO CSAR EDUARDO JAVIER GRANADOS SNCHEZ

Mxico, D.F. Marzo 2015

ASESORA: MAGDALENO VSQUEZ RODRGUEZ

NDICEIMPACT TESTING PRACTICE.

Introduccin..1

Captulo ICHARPY AND IZOD IMPACT TESTING

Summary.Significance and use .Testing machines...Sampling .Number of specimens ..Type and size .Configuration and orientation ..Subsized specimens Preparation of the apparatus ...Temperature control..

Captulo IIPROCEDURE OF CHARPY METHOD

Temperature ..

Positioning ..

Recovering .

Individual test values

Fracture appearance

Lateral expansion

Report.....

Captulo IIIPROCEDURE OF IZOD METHOD

Scope Type of testApparatus Test specimensConditioningProceder Report

Bibliografa..Anexos.

INTRODUCCINImpact testing is a destructive mechanical testing method that measures a samples's ability to resist high-rate loading or absorb the energy of a dynamic impact. In impact testing, a pendulum arm is held at a specific height and then released to hit and break the sample. Its impact strength is determined from the energy absorbed by the sample.The most common method is the Charpy impact test, or Charpy v-notch test, still widely used in industry after more than 100 years in practice, and associated with the standard ASTM A370. Another type of impact test is Izod impact strength testing, most often associated with ASTM D256. Element scientists subject materials and products to dynamic impact, measuring cushioning, g-forces, and impact failure mechanisms. Some laboratories will support quality testing program with accurate testing and reliable turnaround. The advantages of composite materials are numerous and well documented. Composite materials are often used in environments in which they will suffer from impact damage. For example, damage can occur from a hammer being dropped on a composite pipe or from a bullet striking composite armor. Since impact damage resistance is such an important property for composite materials, this chapter will be devoted to the theory behind impact testing, and the procedures used to perform impact testing. The chapter will describe in detail the best way to perform impact tests. Different ways to evaluate impact data will be examined, as well as ways to characterize the impact induced damage.

Impact testing fits into two main categories: (a.) low velocity impact, and (b.) high velocity impact. These two main categories lead to three main types of impact testing. Charpy impact testing and drop weight impact testing fall into the category of low velocity impact testing (here it should be noted that an impact test machine can be used for high velocity impact also; for reference see ASTM D 3763). Ballistics impact testing falls into the category of high velocity impact testing. Technology has increased to the point that there are now sophisticated measuring devices for instrumented impact testing.

For all low velocity instrumented impact test devices there are three major components: the dynamic load cell (or tup), the data display system, and the signal conditioning unit. The tup is placed on the impactor used to strike the specimen. Within the tup is a strain gage that measures the change in strain vs. time as the impactor strikes the specimen. The signal conditioning unit removes the noise associated with the signal, and the data display system plots the measured data. An in-depth exploration on the benefits and methods of each type of impact test will be explored more in the following sections.

CAPTULO ICHARPY AND IZOD IMPACT TESTING

Some types of charts are the same if the procedure is for a special test the autor will emphasize that method is performed.

Summary

A Charpy V-notch impact test is a dynamic test in which a notched specimen is struck and broken by a single blow in a specially designed testing machine. The measuredtest values may be the energy absorbed, the percentage shear fracture, the lateral expansion opposite the notch, or a combination thereof.Charpy impact testing has been used for many years to test the impact toughness of various metals. The advent of modern composites brought about materials with properties that depend on their orientation. Consequently, new test methods had to be found to accurately test the directionally dependent impact resistance of composite materials. Since Charpy impact testing is both cheap and fast, its use was extended to composites. A Charpy impact test machine is shown in the following Figure 1.

Figure 1. Impact Testing Machine For CharpyTesting temperatures other than room (ambient) temperatura often are specified in product or general requirement specifications (hereinafter referred to as the specification). Although the testing temperature is sometimes related to the expected service temperature, the two temperatures need not be identical.

Significance and use

Ductile vs. Brittle BehaviorBody-centered-cubic or ferritic alloys exhibit a significant transition in behavior when impact tested over a range of temperatures. At temperatures above transition, impact specimens fracture by a ductile (usually microvoid coalescence) mechanism, absorbing relatively large amounts of energy. At lower temperatures, they fracture in a brittle (usually cleavage) manner absorbingappreciably less energy. Within the transition range, the fracture will generally be a mixture of areas of ductile fracture and brittle fracture.The temperature range of the transition from one type of behavior to the other varies according to the material being tested. This transition behavior may be defined in various ways for specification purposes.The specification may require a minimum test result for absorbed energy, fracture appearance, lateral expansion, or a combination thereof, at a specified test temperature.The specification may require the determination of the transition temperature at which either the absorbed energy or fracture appearance attains a specified level when testing is performed over a range of temperatures. Alternatively the specification may require the determination of the fracture appearance transition temperature (FATTn) as the temperature at which the required minimum percentage of shear fracture (n) is obtained.

Testing machines

A Charpy impact machine is one in which a notched specimen is broken by a single blow of a freely swinging pendulum. The pendulum is released from a fixed height. Since the height to which the pendulum is raised prior to its swing, and the mass of the pendulum are known, the energy of the blow is predetermined. A means is provided to indicate the energy absorbed in breaking the specimen.The other principal feature of the machine is a fixture (See Fig. 2) designed to support a test specimen as a simple beam at a precise location. The fixture is arranged so that the notched face of the specimen is vertical. The pendulum strikes the other vertical face directly opposite the notch. The dimensions of the specimen supports and striking edge shall conform to Fig. 2. Charpy machines used for testing steel generally have capacities in the 220 to 300 ftlbf (300 to 400 J) energy range. Sometimes machines of lesser capacity are used; however, the capacity of the machine should be substantially in excess of the absorbed energy of the specimens (see Test Methods E 23). The linear velocity at the point of impact should be in the range of 16 to 19 ft/s (4.9 to 5.8 m/s).

All dimensional tolerances shall be 60.05 mm (0.002 in.) unless otherwise specified.NOTE 1A shall be parallel to B within 2:1000 and coplanar with B within 0.05 mm (0.002 in.).NOTE 2C shall be parallel to D within 20:1000 and coplanar with D within 0.125 mm (0.005 in.).NOTE 3Finish on unmarked parts shall be 4 m (125 in.).

Figure 2. Charpy (Simple-Beam) Impact Test

For testing at other than room temperature, it is necessary to condition the Charpy specimens in media at controlled temperatures.Low temperature media usually are chilled fluids (such as water, ice plus water, dry ice plus organic solvents, or liquid nitrogen) or chilled gases.Elevated temperature media are usually heated liquids such as mineral or silicone oils. Circulating air ovens may be used.

Handling EquipmentTongs, especially adapted to fit the notch in the impact specimen, normally are used for removing the specimens from the medium and placing them on the anvil (refer to Test Methods E 23). In cases where the machine fixture does not provide for automatic centering of the test specimen, the tongs may be precision machined to provide centering.

Sampling

Test location and orientation should be addressed by the specifications. If not, for wrought products, the test location shall be the same as that for the tensile specimen and the orientation shall be longitudinal with the notch perpendicular to the major surface of the product being tested.

Number of specimens.

A Charpy impact test consists of all specimens taken from a single test coupon or test location. When the specification calls for a minimum average test result, three specimens shall be tested.When the specification requires determination of a transition temperature, eight to twelve specimens are usually needed.

Type and Size

Use a standard full size Charpy V-notch specimen as shown in Fig. 3, except as allowed in subsized especimens.

Figure 3. Charpy (Simple Beam) Impact Test Specimens

Configuration and orientation

Specimens shall be taken from the material as specified by the applicable specification. Specimen orientation should be designated.The type of specimen chosen depends largely upon the characteristics of the material to be tested. A given specimen may not be equally satisfactory for soft nonferrous metals and hardened steels; therefore, many types of specimens are recognized. In general, sharper and deeper notches are required to distinguish differences in very ductile materials or when using low testing velocities.

The specimens shown in Figs. 4 and 5 are those most widely used and most generally satisfactory. They are particularly suitable for ferrous metals, excepting cast iron. The specimen commonly found suitable for die-cast alloys is shown in Fig. 6.The specimens commonly found suitable for Powder Metallurgy (P/M) materials are shown in Figs. 7 and 8. P/M impact test specimens shall be produced following the procedure in Practice B 925. The impact test results of these materials are affected by specimen orientation. Therefore, unless otherwise specified, the position of the specimen in the machine shall be such that the pendulum will strike a surface that is parallel to the compacting direction. For P/M materials the impact test results are reported as unnotched absorbed impact energy. 7.1.6 Sub-size and supplementary specimen recommendations.

Figure 4. Charpy (Simple-Beam) Impact Test Specimens, Types A, B, And C

Figure 5. Izod (Cantilver-Beam) Impact Test Specimen, Type D

Figure 6. Izod Impact Test Bar for Die Castings Alloys

Figure 7. Unnotched Charpy (Simple Beam) Impact Test Specimen for P/M Structural Materials

Figure 8. Izod (Cantilver-Beam) Impact Test Specimen for P/M Structural Materials

Figure 9. Tubular Impact Specimen Containing Original OD Surface

Figure 10. Determination of Percent Shear Fracture

Subsized specimens

For flat material less than 716 in. (11 mm) thick, or when the absorbed energy is expected to exceed 80 % of full scale, use standard subsize test specimens.For tubular materials tested in the transverse direction, where the relationship between diameter and wall thickness does not permit a standard full size specimen, use standard subsize test specimens or standard size specimens containing outer diameter (OD) curvature as follows:(1) Standard size specimens and subsize specimens may contain the original OD surface of the tubular product as shown in Fig. 9. All other dimensions shall comply with the requirements of Fig. 3.(2) For materials with toughness levels in excess of about 50 ft-lbs, specimens containing the original OD surface may yield values in excess of those resulting from the use of conventional Charpy specimens.

If a standard full-size specimen cannot be prepared, the largest feasible standard subsize specimen shall be prepared.The specimens shall be machined so that the specimen does not include material nearer to the surface than 0.020 in. (0.5 mm).

Tolerances for standard subsize specimens are shown in Fig.3. Standard subsize test specimen sizes are:10 3 7.5 mm, 10 3 6.7 mm, 10 3 5 mm, 10 3 3.3 mm, and 10 3 2.5 mm.Notch the narrow face of the standard subsize specimens so that the notch is perpendicular to the 10 mm wide face.Notch PreparationThe machining of the notch is critical, as it has been demonstrated that extremely minor variations in notch radius and profile, or tool marks at the bottom of the notch may result in erratic test data.

Accuracy and SensitivityCalibrate and adjust Charpy impact machines in accordance with the requirements of Test Methods E 23.

Preparation of the apparatus

Perform a routine procedure for checking impact machines at the beginning of each day, each shift, or just prior to testing on a machine used intermittently. It is recommended that the results of these routine checks be kept in a log book for the machine. After the testing machine has been ascertained to comply with Annex A1 and Annex A2, carry out the routine check as follows:(1) Visually examine the striker and anvils for obvious damage and wear.(2) Check the zero position of the machine by using the following procedure: raise the pendulum to the latched position, move the pointer to near the maximum capacity of the range being used, release the pendulum, and read the indicated value. The pointer should indicate zero on machines Reading directly in energy. On machines reading in degrees, the Reading should correspond to zero on the conversion chart furnished by the machine manufacturer.

(3) On machines that do not compensate for windage and friction losses, the pointer will not indicate zero. In this case, the indicated values, when converted to energy, shall be corrected for frictional losses that are assumed to be proportional to the arc of swing.(4) To ensure that friction and windage losses are within allowable tolerances, the following procedure is recommended: raise the pendulum to the latched position, move the pointer to the negative side of zero, release the pendulum and allow it to cycle five times (a forward and a backward swing together count as one swing), prior to the sixth forward swing, set the pointer to between 5 and 10 % of the scale capacity of the dial, after the sixth forward swing (eleven half swings), record the value indicated by the pointer, convert the reading to energy (if necessary), divide it by 11 (half swings), then divide by the maximum scale value being used and multiply it by 100 to get the percent friction. The result, friction and windage loss, shall not exceed 0.4 % of scale range capacity being tested and should not change by more than 10 % of friction measurements previously made on the machine. If the friction and windage loss value does exceed 0.4 % or is significantly different from previous measurements, check the indicating mechanism, the latch height, and the bearings for wear and damage. However, if the machine has not been used recently, let the pendulum swing for 50 to 100 cycles, and repeat the friction test before undertaking repairs to the machine.

Conditioning: temperature control

When a specific test temperature is required by the specification or purchaser, control the temperature of the heating or cooling medium within 62F (1C). For some steels there may not be a need for this restricted temperature, for example, austenitic steels.Because the temperature of a testing laboratory often varies from 60 to 90F (15 to 32C) a test conducted at room temperature might be conducted at any temperature in this range.

CAPTULO IIPROCEDURE OF CHARPY METHOD

The Charpy test procedure may be summarized as follows: the test specimen is thermally conditioned and positioned on the specimen supports against the anvils; the pendulum is released without vibration, and the specimen is impacted by the striker. Information is obtained from the machine and from the broken specimen.

To position a test specimen in the machine, it is recommended that self-centering tongs similar to those shown in Fig. 11 be used. The tongs illustrated in Fig. 11 are for centering V-notch specimens. If keyhole specimens are used, modification of the tong design may be necessary. If an end-centering device is used, caution must be taken to ensure that low-energy high-strength specimens will not rebound off this device into the pendulum and cause erroneously high recorded values. Many such devices are permanent fixtures of machines, and if the clearance between the end of a specimen in the test position and the centering device is not approximately 13 mm (0.5 in.), the broken specimens may rebound into the pendulum.

To conduct the test, prepare the machine by raising the pendulum to the latched position, set the energy indicator at the maximum scale reading, or initialize the digital display, or both, position the specimen on the anvils, and release the pendulum. If a liquid bath or gas medium is being used for thermal conditioning, perform the following sequence in less than 5 s (for standard 10 3 10 3 55 mm (0.394 3 0.394 3 2.165 in.) specimens. Remove the test specimenfrom its cooling (or heating) medium with centering tongs that have been temperature conditioned with the test specimen, place the specimen in the test position, and, release the pendulum smoothly. If a test specimen has been removed from the temperature conditioning bath and it is questionable that the test can be conducted within the 5 s time frame, return the specimen to the bath for the time required in before testing.

If a fractured impact specimen does not separate into two pieces, report it as unbroken. Unbroken specimens with absorbed energies of less than 80 % of the machine capacity may be averaged with values from broken specimens. If the individual values are not listed, report the percent of unbroken specimens with the average. If the absorbed energy exceeds 80 % of the machine capacity and the specimen passes completely between the anvils, report the value as approximate do not average it with other values. If an unbroken specimen does not pass between the machine anvils, (for example, it stops the pendulum), the result shall be reported as exceeding the machine capacity. A specimen shall never be struck more than once.

If a specimen jams in the machine, disregard the results and check the machine thoroughly for damage or misalignment, which would affect its calibration.To prevent recording an erroneous value, caused by jarring the indicator when locking the pendulum in its upright (ready) position, read the value for each test from the indicator prior to locking the pendulum for the next test.

Temperature

1. Condition the specimens to be broken by holding them in the medium at test temperature for at least 5 min in liquid media and 30 min in gaseous media.2. Prior to each test, maintain the tongs for handling test specimens at the same temperature as the specimen so as not to affect the temperature at the notch.Positioning and Breaking Specimens

3. Carefully center the test specimen in the anvil and release the pendulum to break the specimen.4. If the pendulum is not released within 5 s after removing the specimen from the conditioning medium, do not break the specimen. Return the specimen to the conditioning medium for the period required in the first procedure.

Recovering Specimens

In the event that fracture appearance or lateral expansion must be determined, recover the matched pieces of each broken specimen before breaking the next specimen.

Individual Test Values

5. Impact energy Record the impact energy absorbed to the nearest ftlbf (J)

Fracture Appearance

6. Determine the percentage of shear fracture area by any of the following methods:(1) Measure the length and width of the brittle portion of the fracture surface, as shown in Fig. 10 and determine the percent shear area from either Table 1 or Table 2 depending on the units of measurement.(2) Compare the appearance of the fracture of the specimen with a fracture appearance chart as shown in Fig. 12.(3) Magnify the fracture surface and compare it to a precalibrated overlay chart or measure the percent shear fracture area by means of a planimeter.(4) Photograph the fractured surface at a suitable magnification and measure the percent shear fracture area by means of a planimeter.7. Determine the individual fracture appearance values to the nearest 5 % shear fracture and record the value.

Lateral Expansion

8. Lateral expansion is the increase in specimen width, measured in thousandths of an inch (mils), on the compression side, opposite the notch of the fractured Charpy V-notch specimen as shown in Fig. 13.9. Examine each specimen half to ascertain that the protrusions have not been damaged by contacting the anvil, machine mounting surface, and so forth. Discard such samplessince they may cause erroneous readings.Check the sides of the specimens perpendicular to the notch to ensure that no burrs were formed on the sides during impact testing. If burrs exist, remove them carefully by rubbing on emery cloth or similar abrasive surface, making sure that the protrusions being measured are not rubbed during the removal of the burr.10. Measure the amount of expansion on each side of each half relative to the plane defined by the undeformed portion of the side of the specimen using a gauge similar to that shown in Fig. 14 and Fig. 15.11. Since the fracture path seldom bisects the point of maximum expansion on both sides of a specimen, the sum of the larger values measured for each side is the value of the test.Arrange the halves of one specimen so that compression sides are facing each other. Using the gauge, measure the protrusin on each half specimen, ensuring that the same side of the specimen is measured. Measure the two broken halves individually.Repeat the procedure to measure the protrusions on the opposite side of the specimen halves. The larger of the two values for each side is the expansion of that side of the specimen.12. Measure the individual lateral expansion values to the nearest mil (0.025 mm) and record the values.13. With the exception described as follows, any specimen that does not separate into two pieces when struck by a single blow shall be reported as unbroken. If the specimen can be separated by force applied by bare hands, the specimen may be considered as having been separated by the blow.

Figure 11. Centering Tongs for V-Notch Charpy Specimens

Figure 12. Fracture Appearance Charts and Percent Shear Fracture Comparator

Figure 13. Halves of Broken Charpy V-Notch Impact Specimen Joined for the Measurement of Lateral Expansion, Dimension A

Figure 14. Lateral Expansion Gauge for Charpy Impact Specimens

Figure 15. Charpy V-Notch Test Acceptance Criteria for Various Sub-Size Specimens

Table 1. Percent Shear for Measurements Made in Millimetres

Table 2. Percent Shear for Measurements Made in Inches

Table 3. Charpy V-Notch Test Acceptance Criteria for Various Sub-Size Specimens

Test resultWhen the acceptance criterion of any impact test is specified to be a minimum average value at a given temperature, the test result shall be the average (arithmetic mean) of the individual test values of three specimens from one test location.

1. When a minimum average test result is specified:1.1 The test result is acceptable when all of the below are met:(1) The test result equals or exceeds the specified minimum average (given in the specification),(2) The individual test value for not more than one specimen measures less than the specified minimum average, and(3) The individual test value for any specimen measures not less than two-thirds of the specified minimum average.1.2 If the acceptance requirements of 1.1 are not met, perform one retest of three additional specimens from the same test location. Each individual test value of the retested specimens shall be equal to or greater than the specified minimum average value.

2. Test Specifying a Minimum Transition Temperature

2.1 Definition of Transition TemperatureFor specification purposes, the transition temperature is the temperature at which the designated material test value equals or exceeds a specified minimum test value.2.2 Determination of Transition Temperature:2.2.1 Break one specimen at each of a series of temperatures above and below the anticipated transition temperature using the procedures in Section 1. Record each test temperature to the nearest 1F (0.5C).2.2.2 Plot the individual test results (ftlbf or percent shear) as the ordinate versus the corresponding test temperature as the abscissa and construct a best-fit curve through the plotted data points.2.2.3 If transition temperature is specified as the temperature at which a test value is achieved, determine the temperature at which the plotted curve intersects the specified test value by graphical interpolation (extrapolation is not permitted). Record this transition temperature to the nearest 5F (3C). If the tabulated test results clearly indicate a transition temperature lower than specified, it is not necessary to plot the data. Report the lowest test temperature for which test value exceeds the specified value.2.2.4 Accept the test result if the determined transition temperature is equal to or lower than the specified value.

2.2.5 If the determined transition temperature is higher than the specified value, but not more than 20F (12C) higher than the specified value, test sufficient samples in accordance with Section 1 to plot two additional curves. Accept the test results if the temperatures determined from both additional tests are equal to or lower than the specified value.3. When subsize specimens are permitted or necessary, or both, modify the specified test requirement according to Table 9 or test temperature according to ASME Boiler and Pressure Vessel Code, Table UG-84.2, or both. Greater energies or lower test temperatures may be agreed upon by purchaser and supplier.

Records

1. The test record should contain the following information as appropriate:1.1 Full description of material tested (that is, specification number, grade, class or type, size, heat number).1.2 Specimen orientation with respect to the material axis.1.3 Specimen size.1.4 Test temperature and individual test value for each specimen broken, including initial tests and retests.1.5 Test results.1.6 Transition temperature and criterion for its determination, including initial tests and retests.

Report

1. The specification should designate the information to be reported.

CAPTULO IIIPROCEDURE OF IZOD METHOD1. SCOPE

These test methods cover the determination of the resistance of plastics to standardized (see Note 1) pendulumtype hammers, mounted in standardized machines, in breaking standard specimens with one pendulum swing (see Note 2).The standard tests for these test methods require specimens made with a milled notch (see Note 3). In Test Methods A, C, and D, the notch produces a stress concentration that increases the probability of a brittle, rather than a ductile, fracture. In Test Method E, the impact resistance is obtained breakage byflexural shock as indicated by the energy extracted from by reversing the notched specimen 180 in the clamping vise. The results of all test methods are reported in terms of energy absorbed per unit of specimen width or per unit of crosssectional area under the notch. (see Note 4).

NOTE 1The machines with their pendulum-type hammers have been standardized in that they must comply with certain requirements, including a fixed height of hammer fall that results in a substantially fixed velocity of the hammer at the moment of impact. However, hammers of different initial energies (produced by varying their effective weights) are recommended for use with specimens of different impact resistance.Moreover, manufacturers of the equipment are permitted to use different lengths and constructions of pendulums with possible differences in pendulum rigidities resulting. (See Section 5.) Be aware that other differences in machine design may exist. The specimens are standardized in that they are required to have one fixed length, one fixed depth, and one particular design of milled notch. The width of the specimens ispermitted to vary between limits.

NOTE 2Results generated using pendulums that utilize a load cell to record the impact force and thus impact energy, may not be equivalent to results that are generated using manually or digitally encoded testers that measure the energy remaining in the pendulum after impact.

NOTE 3The notch in the Izod specimen serves to concentrate the stress, minimize plastic deformation, and direct the fracture to the part of the specimen behind the notch. Scatter in energy-to-break is thus reduced. However, because of differences in the elastic and viscoelastic properties of plastics, response to a given notch varies among materials. A measure of a plastics notch sensitivity may be obtained with Test Method D by comparing the energies to break specimens having different radii at the base of the notch.

NOTE 4Caution must be exercised in interpreting the results of these standard test methods. The following testing parameters may affect test results significantly. Method of fabrication, including but not limited to processing technology, molding conditions, mold design, and termal treatments, method of notching, speed of notching tool, testing of notching apparatus; Quality of the notch; Time between notching and test, Test specimen thickness, Test specimen width under notch, and environmental conditioning. The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only. This standard does not purport to address all of the safety concerns, if any, associated with its use. It is the responsibility of the user of this standard to establish appropriate safety and health practices and determine the applicability of regulatory limitations prior to use.

NOTE 5These test methods resemble ISO 180:1993 in regard to title only. The contents are significantly different.

2. TYPE OF TEST

Four similar methods are presented in these test methods. (See Note 6.) All test methods use the same testing machine and specimen dimensions. There is no known means for correlating the results from the different test methods.

NOTE 6Test Method B for Charpy has been removed and is being revised under a new standard.

2.1 In Test Method A, the specimen is held as a vertical cantilever beam and is broken by a single swing of the pendulum. The line of initial contact is at a fixed distance from the specimen clamp and from the centerline of the notch and on the same face as the notch.

2.2 Test Method C is similar to Test Method A, except for the addition of a procedure for determining the energy expended in tossing a portion of the specimen. The value reported is called the estimated net Izod impact resistance. Test Method C is preferred over Test Method A for materials that have an Izod impact resistance of less than 27 J/m (0.5 ftlbf/in.) under notch. The differences between Test Methods A and C become unimportant for materials that have an Izod impact resistance higher than this value.

2.3 Test Method D provides a measure of the notch sensitivity of a material. The stress-concentration at the notch increases with decreasing notch radius.

2.3.1 For a given system, greater stress concentration results in higher localized rates-of-strain. Since the effect of strain-rate on energy-to-break varies among materials, a measure of this effect may be obtained by testing specimens with different notch radio.2.3.2 In the Izod-type test it has been demonstrated that the function, energy-to-break versus notch radius, is reasonably linear from a radius of 0.03 to 2.5 mm (0.001 to 0.100 in.), provided that all specimens have the same type of break. (See 5.8 and 22.1.).

2.3.3 For the purpose of this test, the slope, b (see 22.1), of the line between radii of 0.25 and 1.0 mm (0.010 and 0.040 in.) is used, unless tests with the 1.0-mm radius give nonbreak results. In that case, 0.25 and 0.50-mm (0.010 and 0.020-in.) radii may be used. The effect of notch radius on the impact energy to break a specimen under the conditions of this test is measured by the value b. Materials with low values of b, whether high or low energy-to-break with the standard notch, are relatively insensitive to differences in notch radius; while the energy-to-break materials with high values of b is highly dependent on notch radius.

2.3.4 The parameter b cannot be used in design calculations but may serve as a guide to the designer and in selection of materials.

2.4 Test Method E is similar to Test Method A, except that the specimen is reversed in the vise of the machine 180 to the usual striking position, such that the striker of the apparatus impacts the specimen on the face opposite the notch. (See Fig. 1, Fig. 2.) Test Method E is used to give an indication of the unnotched impact resistance of plastics; however, results obtained by the reversed notch method may not always agree with those obtained on a completely unnotched specimen.

FIG. 1 Relationship of Vise, Specimen, and Striking Edge to Each Other for Izod Test Methods A and C

FIG. 2 Relationship of vise, specimen, and striking edge to each other for test method e, test method acantilever beam test

3. APPARATUS

3.1 The machine shall consist of a massive base on which is mounted a vise for holding the specimen and to which is connected, through a rigid frame and bearings, a pendulumtype hammer. (See 6.2.) The machine must also have a pendulum holding and releasing mechanism and a pointer and dial mechanism for indicating the excess energy remaining in the pendulum after breaking the specimen. Optionally, an electronic digital display or computer can be used in place of the dial and pointer to measure the energy loss and indicate the breaking energy of the specimen.

3.2 A jig for positioning the specimen in the vise and graphs or tables to aid in the calculation of the correction for friction and windage also should be included. One type of machine is shown in Fig. 3. One design of specimen-positioning jig is illustrated in Fig. 4. Detailed requirements are given in subsequent paragraphs. General test methods for checking and calibrating the machine. Additional instructions for adjusting a particular machine should be supplied by the manufacturer.

3.3 The pendulum shall consist of a single or multimembered arm with a bearing on one end and a head, containing the striker, on the other. The arm must be sufficiently rigid to maintain the proper clearances and geometric relationships between the machine parts and the specimen and to minimize vibrational energy losses that are always included in the measured impact resistance. Both simple and compound pendulum designs may comply with this test method.3.4 The striker of the pendulum shall be hardened steel and shall be a cylindrical surface having a radius of curvature of 0.80 6 0.20 mm (0.031 6 0.008 in.) with its axis horizontal and perpendicular to the plane of swing of the pendulum. The line of contact of the striker shall be located at the center of percussion of the pendulum within 62.54 mm (60.100 in.)

FIG. 3 Cantilever Beam (Izod-Type) Impact Machine

FIG. 4 Jig for Positioning Specimen for Camping

(See Note 9.) Those portions of the pendulum adjacent to the cylindrical striking edge shall be recessed or inclined at a suitable angle so that there will be no chance for other than this cylindrical surface coming in contact with the specimen during the break.

NOTE 9The distance from the axis of support to the center of percussion may be determined experimentally from the period of small amplitude oscillations of the pendulum by means of the following equation:

where:

L = distance from the axis of support to the center of percussion, m or (ft),g = local gravitational acceleration (known to an accuracy of one part in one thousand), m/s2 or (ft/s2), = 3.1416 (42 = 39.48), andp = period, s, of a single complete swing (to and fro) determined by averaging at least 20 consecutive and uninterrupted swings. The angle of swing shall be less than 5 each side of center.

3.5 The position of the pendulum holding and releasing mechanism shall be such that the vertical height of fall of the striker shall be 610 6 2 mm (24.0 6 0.1 in.). This will produce a velocity of the striker at the moment of impact of approximately 3.5 m (11.4 ft)/s. (See Note 10.) The mechanism shall be so constructed and operated that it will release the pendulum without imparting acceleration or vibration to it.

NOTE 10

Where:

V = velocity of the striker at the moment of impact (m/s),g = local gravitational acceleration (m/s2), andh = vertical height of fall of the striker (m).This assumes no windage or friction.

3.6 The effective length of the pendulum shall be between 0.33 and 0.40 m (12.8 and 16.0 in.) so that the required elevation of the striker may be obtained by raising the pendulum to an angle between 60 and 30 above the horizontal.

3.7 The machine shall be provided with a basic pendulum capable of delivering an energy of 2.7 6 0.14 J (2.00 6 0.10 ftlbf). This pendulum shall be used with all specimens that extract less than 85 % of this energy. Heavier pendulums shall be provided for specimens that require more energy to break.

These may be separate interchangeable pendulums or one basic pendulum to which extra pairs of equal calibrated weights may be rigidly attached to opposite sides of the pendulum. It is imperative that the extra weights shall not significantly change the position of the center of percussion or the free-hanging rest point of the pendulum (that would consequently take the machine outside of the allowable calibration tolerances). A range of pendulums having energies from 2.7 to 21.7 J (2 to 16 ftlbf) has been found to be sufficient for use with most plastic specimens and may be used with most machines. A series of pendulums such that each has twice the energy of the next will be found convenient. Each pendulum shall have an energy within 60.5 % of its nominal capacity.

3.8 A vise shall be provided for clamping the specimen rigidly in position so that the long axis of the specimen is vertical and at right angles to the top plane of the vise. (See Fig.1.) This top plane shall bisect the angle of the notch with a tolerance of 0.12 mm (0.005 in.). Correct positioning of the specimen is generally done with a jig furnished with the machine. The top edges of the fixed and moveable jaws shall have a radius of 0.25 6 0.12 mm (0.010 6 0.005 in.). For specimens whose thickness approaches the lower limiting value of 3.00 mm (0.118 in.), means shall be provided to prevent the lower half of the specimen from moving during the clamping or testing operations (see Fig. 4 and Note 11.)

NOTE 11Some plastics are sensitive to clamping pressure; therefore, cooperating laboratories should agree upon some means of standardizing the clamping force. One method is using a torque wrench on the screw of the specimen vise. If the faces of the vise or specimen are not flat and parallel, a greater sensitivity to clamping pressure may be evident. See the calibration procedure in for adjustment and correction instructions for faulty instruments.

3.9 When the pendulum is free hanging, the striking surface shall come within 0.2 % of scale of touching the front face of a standard specimen. During an actual swing this element shall make initial contact with the specimen on a line 22.00 6 0.05 mm (0.87 6 0.002 in.) above the top surface of the vise.

3.10 Means shall be provided for determining the energy expended by the pendulum in breaking the specimen. This is accomplished using either a pointer and dial mechanism or an electronic system consisting of a digital indicator and sensor (typically an encoder or resolver). In either case, the indicated breaking energy is determined by detecting the height of rise of the pendulum beyond the point of impact in terms of energy removed from that specific pendulum. Since the indicated energy must be corrected for pendulum-bearing friction, pointer friction, pointer inertia, and pendulum windage. (See Note 12.)

NOTE 12Many digital indicating systems automatically correct for windage and friction. The equipment manufacturer may be consulted for details concerning how this is performed, or if it is necessary to determine the means for manually calculating the energy loss due to windage and friction.

3.11 The vise, pendulum, and frame shall be sufficiently rigid to maintain correct alignment of the hammer and specimen, both at the moment of impact and during the propagation of the fracture, and to minimize energy losses due to vibration. The base shall be sufficiently massive that the impact will not cause it to move. The machine shall be so designed, constructed, and maintained that energy losses due to pendulum air drag (windage), friction in the pendulum bearings, and friction and inertia in the indicating mechanism are held to a minimum.

3.12 A check of the calibration of an impact machine is difficult to make under dynamic conditions. The basic parameters are normally checked under static conditions; if the machine passes the static tests, then it is assumed to be accurate. The calibration procedure should be used to establish the accuracy of the equipment. However, for some machine designs it might be necessary to change the recommended method of obtaining the required calibration measurements. Other methods of performing the required checks may be substituted, provided that they can be shown to result in an equivalent accuracy. also describes a dynamic test for checking certain features of the machine and specimen.

3.13 MicrometersApparatus for measurement of the width of the specimen shall comply with the requirements of Test Methods D5947. Apparatus for the measurement of the depth of plastic material remaining in the specimen under the notch shall comply with requirements of Test Methods D5947, provided however that the one anvil or presser foot shall be a tapered blade conforming to the dimensions given in Fig. 5.The opposing anvil or presser foot shall be flat and conforming to Test Methods D5947.

FIG. 5 Early (ca. 1970) Version of a Notch-Depth tMicrometer

NOTE 1These views not to scale.NOTE 2Micrometer to be satin-chrome finished with friction thimble.NOTE 3Special anvil for micrometer caliper 0 to 25.4 mm range (50.8 mm frame) (0 to 1 in. range (2-in. frame)).NOTE 4Anvil to be oriented with respect to frame as shown.NOTE 5Anvil and spindle to have hardened surfaces.NOTE 6Range: 0 to 25.4 mm (0 to 1 in. in thousandths of an inch).NOTE 7Adjustment must be at zero when spindle and anvil are in contact.

FIG. 6 Dimensions of Izod-Type Test Specimenmm in.A 10.16 0.05 0.400 0.002B 31.8 1.0 1.25 0.04C 63.5 2.0 2.50 0.08D 0.25R 0.05 0.010R 0.002E 12.70 0.20 0.500 0.008

4. TEST SPECIMENS

4.1 Studies have shown that, for some materials, the location of the notch on the specimen and the length of the impacted end may have a slight effect on the measured impact resistance. Therefore, unless otherwise specified, care must be taken to ensure that the specimen conforms to the dimensions shown in Fig. 6 and that it is positioned as shown in Fig. 1 or Fig. 2.

4.2 Molded specimens shall have a width between 3.0 and 12.7 mm (0.118 and 0.500 in.). Use the specimen width as specified in the material specification or as agreed upon between the supplier and the customer. All specimens having one dimension less than 12.7 mm (0.500 in.) shall have the notch cut on the shorter side. Otherwise, all compressionmolded specimens shall be notched on the side parallel to the direction of application of molding pressure. (See Fig. 6.).

4.3 For sheet materials, the specimens shall be cut from the sheet in both the lengthwise and crosswise directions unless otherwise specified. The width of the specimen shall be the thickness of the sheet if the sheet thickness is between 3.0 and 12.7 mm (0.118 and 0.500 in.). Sheet material thicker than 12.7 mm shall be machined down to 12.7 mm. Specimens with a 12.7-mm square cross section may be tested either edgewise or flatwise as cut from the sheet. When specimens are tested flatwise, the notch shall be made on the machined surface if the specimen is machined on one face only. When the specimen is cut from a thick sheet, notation shall be made of the portion of the thickness of the sheet from which the specimen was cut, for example, center, top, or bottom surface.

4.4 The practice of cementing, bolting, clamping, or otherwise combining of substandard width to form a composite test specimen is not recommended and should be avoided since test results may be seriously affected by interface effects or effects of solvents and cements on energy absorption of composite test specimens, or both. However, if Izod test data on such thin materials are required when no other means of preparing specimens are available, and if possible sources of error are recognized and acceptable, the following technique of preparing composites may be utilizad.

4.5 Each specimen shall be free of twist (see Note 14) and shall have mutually perpendicular pairs of plane parallel surfaces and free from scratches, pits, and sink marks. The specimens shall be checked for compliance with these requirements by visual observation against straightedges, squares, and flat plates, and by measuring with micrometer calipers. Any specimen showing observable or measurable departure from one or more of these requirements shall be rejected or machined to the proper size and shape before testing.

5. CONDITIONING

5.1 ConditioningCondition the test specimens at 23 6 2C (73 6 3.6F) and 50 6 10 % relative humidity for not less than 40 h after notching and prior to testing in accordance with Procedure A of Practice D618, unless it can be documented (between supplier and customer) that a shorter conditioning time is sufficient for a given material to reach equilibrium of impact resistance.

5.1.1 Note that for some hygroscopic materials, such as nylons, the material specifications (for example, Specification D4066) call for testing dry as-molded specimens. Such requirements take precedence over the above routine preconditioning to 50 % relative humidity and require sealing the specimens in water vapor-impermeable containers as soon as molded and not removing them until ready for testing.

5.2 Test ConditionsConduct tests in the standard laboratory atmosphere of 23 6 2C (73 6 3.6F) and 50 6 10 % relative humidity, unless otherwise specified in the material specification or by customer requirements. In cases of disagreement, the tolerances shall be 61C (61.8F) and 6 5 % relative humidity.

6. PROCEDER

6.1 At least five and preferably ten or more individual determinations of impact resistance must be made on each sample to be tested under the conditions prescribed in Section 5. Each group shall consist of specimens with the same nominal width (60.13 mm (60.005 in.)). In the case of specimens cut from sheets that are suspected of being anisotropic, prepare and test specimens from each principal direction (lengthwise and crosswise to the direction of anisotropy).

6.2 Estimate the breaking energy for the specimen and select a pendulum of suitable energy. Use the lightest standard pendulum that is expected to break each specimen in the group with a loss of not more than 85 % of its energy. Check the machine with the proper pendulum in place for conformity with the requirement.

6.3 If the machine is equipped with a mechanical pointer and dial, perform the following operations before testing the specimens. If the machine is equipped with a digital indicating system, follow the manufacturers instructions to correct for windage and friction. If excessive friction is indicated, the machine shall be adjusted before starting a test.

6.3.1 With the indicating pointer in its normal starting position but without a specimen in the vise, release the pendulum from its normal starting position and note the position the pointer attains after the swing as one reading of Factor A.

6.3.2 Without resetting the pointer, raise the pendulum and release again. The pointer should move up the scale an additional amount. Repeat (10.3.2) until a swing causes no additional movement of the pointer and note the final Reading as one reading of Factor B.

6.3.3 Repeat the preceding two operations several times and calculate and record the average A and B readings.

6.4 Check the specimens for conformity with the requirements of Sections 3, 4.

6.5 Measure and record the width of each specimen after notching to the nearest 0.025 mm (0.001 in.). Measure the width in one location adjacent to the notch centered about the anticipated fracture plane.

6.6 Measure and record the depth of material remaining in the specimen under the notch of each specimen to the nearest 0.025 mm (0.001 in.). The tapered blade will be fitted to the notch. The specimen will be approximately vertical between the anvils. For specimens with a draft angle, position edge of the non-cavity (wider edge) surface centered on the micrometers flat circular anvil.

6.7 10.7 Position the specimen precisely (see 6.7) so that it is rigidly, but not too tightly (see Note 11), clamped in the vise. Pay special attention to ensure that the impacted end of the specimen as shown and dimensioned in Fig. 6 is the end projecting above the vise. Release the pendulum and record the indicated breaking energy of the specimen together with a description of the appearance of the broken specimen (see failure categories in 5.8).

6.8 Subtract the windage and friction correction from the indicated breaking energy of the specimen, unless determined automatically by the indicating system (that is, digital display or computer). If a mechanical dial and pointer is employed, use the A and B factors and the appropriate tables or the graph described in Annex A1 and Annex A2 to determine the correction. For those digital systems that do not automatically compensate for windage and friction, follow the manufacturers procedure for performing this correction.6.8.1 In other words, either manually or automatically, the windage and friction correction value is subtracted from the uncorrected, indicated breaking energy to obtain the new breaking energy. Compare the net value so found with the energy requirement of the hammer specified in 10.2. If a hammer of improper energy was used, discard the result and make additional tests on new specimens with the proper hammer.

6.9 Divide the net value found in 6.8 by the measured width of the particular specimen to obtain the impact resistance under the notch in J/m (ftlbf/in.). If the optional units of kJ/m2 (ftlbf/in.2) are used, divide the net value found in 10.8 by the measured width and depth under the notch of the particular specimen to obtain the impact strength. The term, depth under the notch, is graphically represented by Dimension A in Fig. 6. Consequently, the cross-sectional area (width times depth under the notch) will need to be reported.

6.10 Calculate the average Izod impact resistance of the group of specimens. However, only values of specimens having the same nominal width and type of break may be averaged. Values obtained from specimens that did not break in the manner specified in 5.8 shall not be included in the average. Also calculate the standard deviation of the group of values.

7. REPORT

7.1 Report the following information:

7.1.1 The test method used (Test Method A, C, D, or E).

7.1.2 Complete identification of the material tested, including type source, manufacturers code number, and previous history.

7.1.3 A statement of how the specimens were prepared, the testing conditions used, the number of hours the specimens were conditioned after notching, and for sheet materials, the direction of testing with respect to anisotropy.

7.1.4 The capacity of the pendulum in joules, or foot pound-force, or inch pound-force.

7.1.5 The width and depth under the notch of each specimen tested.

7.1.6 The total number of specimens tested per sample of material.

7.1.7 The type of faiulre.

7.1.8 The impact resistance must be reported in J/m (ftlbf/in.); the optional units of kJ/m2 (ftlbf/in.2) may also be required.

7.1.9 The number of those specimens that resulted in failures which conforms to each of the requirement categories.The average impact resistance and standard deviation (in J/m (ftlbf/in.)) for those specimens in each failure category, except non-break as presented. Optional units (kJ/m2 (ftlbf/in.2)) may also need to be reported.

7.1.10 The percent of specimens failing in each category suffixed by the corresponding letter code.

BIBLIOGRAFA

ASTM A 370 09a Standard Test Methods and Definitions for Mechanical Testing of Steel Products.

ASTM E 23 07a Standard Test Methods for Notched Bar Impact Testing of Metallic Materials.

BS 131 Calibration of Impact Testing Machines for metals.

BS 131 Determination of Crystallinity.

BS 131Method for Precision Determination of Charpy-V Impact Energy.

BS 131Specification for Verification of Precision Test Machines.

EN 875 Destructive Tests on Welds in Metallic Materials - Impact Tests.

EN 10045 Test Method.

EN 10045 Verification of Impact Testing Machines.

ANEXOS