Astm stp 466 1970 (1984)

IMPACT TESTING OF METALS A symposium presented at the Seventy-second Annual Meeting AMERICAN SOCIETY FOR TESTING AND MATERIALS Atlantic City, N J., 22-27 June 1969 ASTM SPECIAL TECHNICAL PUBLICATION 466 ITI AMERICAN SOCIETY FOR TESTING AND MATERIALS 1916 Race Street, Philadelphia, Pa 19103 Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized (~) BY AMERICAN SOCIETY FOR TESTING AND ~IATERIALS 1970 Library of Congress Catalog Card Number: 74-97731 ISBN 0-8031-0038-8 NOTE The Society is not responsible, as a body, for the statements and opinions advanced in this publication Primed in York, Pa March 1970 Second Priming, Ba[timore,Md October 1984 Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized Foreword The papers in the Symposium on Impact Testing of ~{etals were given at the Seventy-second Annual 5Ieeting of the American Society for Testing and 5Iater als held in Atlantic City, N J., 22-27 June 1969 The sponsors of this symposium were Committee E-1 on 5Iethods of Testing, Subcommittee on Impact Testing, and Committee E-24 on Fracture Testing of 5Ietals D E Driscoll, Army 5Iaterials and Mechanics Research Center, presided as symposium chairman Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions a Related ASTM Publications Evaluation of Wear Testing, STP 446 (1969) Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized Contents Introduction T he Role of Impact Testing in Characterizing the Toughness of Materials w T ~ATrHEWS Effect of Strength and Thickness on Notch Ductility J m GROSS Discussion An Evaluation of the Charpy Impact Test r HARSEMAND H W'INTERMARK 21 The Charpy Impact T e s t - - I t s Accuracy and Factors Affecting Test Results raN H FAH~Y Discussion Measurement of Fracture Toughness by Instrumented Impact T e s t - c E TURNER 50 53 76 89 93 Materials Sensitive to Slow Rates of Straining c E HARrBOWER 113 Applications of the Instrumented Charpy Impact Test R A WULLAERT 148 Influence of Inertial Load in Instrumental Impact Tests s VENZI, A H PRIEST~ AND M J MAY Significance of the Drop-Weight Tear Test and Charpy V-Notch Impact Test Results R J EIBER, A ~ DUFFY, AND G M MCCLURE 165 181 Investigation of Transition Temperature Tests for Line Pipe M a t e r i a l s - E B NORRIS AND R D WYLIE 192 Drop-Weight Tear T e s t - - E f f e c t of Variables on Test Results T G HEBERLING A N D G E S E L B Y 224 Dynamic Tear E n e r g y - - A Practical Performance Criterion for Fracture Resistance -E A L A N G E A N D F J L O S S 241 Dynamic Fracture Toughness Tests on A302-B Steel A J BUSH 259 Correlations Between K~o and Charpy V-Notch Test Results in the Transition-Temperature Range J M RANSOMAND S W ROLFE 281 Development of a Pendulum-Type w F FRANZ Dynamic Tear-Test Machine 303 General Discussion 314 Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions autho STP466-EB/Mar 1970 Introduction Since the last ASTM Symposium on Impact Testing in 1955, there has been considerable effort expended relative to the merits of impact testing, particularly with regard to the Charpy V-notch test Yet, the Charpy test continues to play an important part in many materials specifications To gain a clearer understanding of what an impact test tells us, many investigations have been conducted These range from changing the configuration of the notch in the Charpy specimen to designing new specimens and tests for measuring toughness In impact testing, for example, the most recent advances are in the areas of instrumentation of Charpy equipment and modification of specimen geometry Both advances are aimed to provide a clearer understanding of the impact test itself or to attempt to find meaningful correlations between the various fracture toughness criteria or both Not to be overlooked are those efforts aimed at understanding the effects of test and specimen variables on the resultant test values Coupled with these efforts have been modifications of the various tests or the implementation of new tests, such as the dynamic tear (DT) test, which now finds considerable application in the pressure vessel field Fracture toughness investigations have been the cause of considerable discussion since the 1955 symposium Due to the interest and response to this year's symposium, four sessions were required, and their classification best expresses the theme of the symposium In the first session, after the opening paper reviews the role that the various impact tests play in characterizing the toughness of materials, the remaining papers discuss various aspects of the standard Charpy test from the effects of material strength and thickness to the accuracy of the test itself and the factors affecting test results The second session is directed largely to the use of instrumentation to record load versus time and aimed at measuring the various fracture toughness parameters The last two sessions deal with the drop-weight and dynamic tear tests The papers are quite diversified, ranging from applicable equipment, to effects of test variables, to correlations between the various tear tests or the Charpy test or both Copyright by ASTM Int'l (all rights reserved); Sat Dec 51 09:47:03 EST 2015 Downloaded/printed by ASTM International Copyright 1970 by www.aslm.org University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized IMPACTTESTING OF METALS All of the above have contributed to the broadened scope of the current symposium The end result is an excellent balance between theory and experimental results for the various means of assessing toughness D E Driscoll Chief, Quality Assurance Division, Army Materials and :~'[eehanics Research Center, Watertown, Mass 02172; symposium chairman Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions auth W T Matthews ~ The Role of Impact Testing in Characterizing the Toughness of Materials REFERENCE: Matthews, W T., "The Role of I m p a c t Testing in Characterizing the Toughness of Materials," Impact Testing of Metals, A S T M STP ~66, American Society for Testing and Materials, 1970, pp 3-20 ABSTRACT: The objectives of fracture toughness testing are to provide information for design, screening, and acceptance of materials Several tests are discussed in relation to an ideal design test possessing quantitativeness and generality: slow and impact-loaded Griffith-Irwin fracture mechanics, conventional Charpy, and drop-weight tear testing (DWTT) The features and limitations of these methods are noted Fracture mechanics is recommended for testing relatively brittle materials and DWTT and associated procedures as the best available for tough materials Probable increased development in quantitative fracture mechanics including impact testing is discussed For screening and acceptance, conventional Charpy testing is recommended provided that correlation with more basic tests has been established KEY WORDS: testing, toughness, design, impact tests, transition temperature, fractures (materials), fracture mechanics, loads (forces), evaluation, tests Since the last A S T M Symposium on I m p a c t in 1955, there has continued to be considerable research effort in the field of fracture and fatigue New approaches have been developed and existing methods expanded I n order to assess the significance of this wide variety of methods and associated testing procedures for the prevention of fracture, several excellent summaries have been published [1,2,3] ~ I t is appropriate as an introduction to this symposium to follow a similar approach with special attention given to the role of impact tests The following discussion will draw upon the past summaries and, in addition, will consider more recent developments, such as the use of a C h a r p y - t y p e impact specimen for measuring fracture toughness.3 1Mechanical engineer, Theoretical and Applied Mechanics Research Laboratory, Army Materials and Mechanics Research Center, Watertown, Mass 02172 The italic numbers in brackets refer to the list of references appended to this paper 3In this paper "fracture toughness" refers to parameter defined by linear elastic fracture mechanics Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed Copyright9 1970by by ASTMInternational www.astm.org University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized IMPACT TESTING OF METALS ~Iaterial toughness tests are conducted to provide information for design and for acceptance and screening of materials In this paper the emphasis will be almost entirely on methods of testing to provide information for design, since in design we are dealing with the end result of the characterization of material properties, which therefore imposes the most stringent requirements on the reliability of our design philosophy and associated tests We will deal only briefly with the use of impact tests for acceptance and screening of material Material Toughness Testing for Design We will trace the evolution of "design against fracture" philosophies and associated tests in order to indicate the usefulness of various approaches to design Based on the capabilities of these approaches, we will assess the role of impact testing in characterizing the toughness of materials for design Since this field is so broad, the discussion will be streamlined arbitrarily to limit attention to the most general procedures This description will illustrate that, despite the development of new methods, we are still unable to deal satisfactorily with many materials We will begin with the standard textbook approach to design calculations Ste~gth of Materials Approach The classical strength of materials procedure calculates the loadcarrying capacity of a structural member on the basis of some percentage of the gross, static yield stress of the selected material as it is measured by a smooth uniaxial tension specimen The inherent toughness of the material is counted upon to redistribute any large local stresses which may occur This method suffers from the inability of the smooth tension test to reveal whether the material will display inadequate toughness when subiected to combinations of tow temperature, high rates of loading, and triaxial stress state as might be imposed by a sharp notch or crack Hence, catastrophic failures can occur as a result of large local stresses although the gross stress levels are small To overcome this difficulty, new concepts and tests were devised to reveal the toughness of materials when subjected to severe conditions Tra~sition Temperature Approach The transition temperature approach as applied to design deals only with the behavior of the material The object of the method is to guarantee that the material possesses sufficient toughness when subjected to severe conditions to allow the load-carrying capability of a structural member to be calculated by strength of materials methods without further regard for the toughness of the material or the consequences of small flaws in the structure It is necessary to devise a criterion which will ensure that Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further re 302 IMPACT TESTING OF METALS I 40 w 30 I I I [ I SLOW-SEND D IMPACT SO a I w ~ ao B no o Q ~ o IO I -500 I -250 I -200 I -150 I -I00 L I L -50 SO t I00 TEST TEMPERATURE, F FIG 23 S~w-bend and impact CVN ~st resul~ for 18Ni(~50) ~teel References [1] Williams, M L., "Analysis of Brittle Behavior in Ship P|ates," Ship Structure Committee Report, Serial No NBS-5, Feb 1955 (also included in Effect of Temperature on the Brittle Behavior of Metals with Particular Reference to Low Temperature, ASTM STP 158, American Society for Testing and Materials, 1954, pp 11-44) [~1 Rolfe, S T and Gensamer, M., "Fracture-Toughness Requirements for Steels," AD 835 923L, 20 Sept 1968 (available from Defense Documentation Center) [3] Barsom, J M and Rolfe, S T., "KIr Transition-Temperature Behavior of A517-F Steel," AD 846 124L, 29 Nov 1968 (available from Defense Documentation Center) [4] Shoemaker, A K and Rolfe, S T., "The Static and Dynamic Low-Temperature Crack-Toughness Performance of Seven Structural Steels," AD 846 126L, 29 Nov 1968 (available from Defense Documentation Center.) [5] Brown, W F., Jr., and Srawley, J E., Plane Strain Crack Toughness Testing of High-Strength Metallic Malerials, ASTM STP 410, American Society for Testing and Materials, 1967 [61 Clausing, D P., "Effect of Plane-Strain Sensitivity on the Charpy Toughness of Structural Steels," AD 836 314L, 15 May 1968 (available from Defense Documentation Center) [7] Hollomon, J H., "The Notched-Bar Impact Test," Transactions, American Institute of Mining, Metallurgical, and Petroleum Engineers, Vol 158, 1944, pp 310-322 [8] Rolfe, S T and Novak, S R., "Slow-Bend Kxo Testing of Medium-Strength High-Toughness Steels," AD 817 373L, Aug 1967 (available from Defense Documentation Center) [9] Greenberg, H D., Wessel, E T., and Pryle, W H., "Fracture Toughness of Turbine-Generator Rotor Forgings," presented at the Second National Symposium on Fracture Mechanics, Lehigh University, Bethlehem, Pa., 17-19, June 1968 [10] Burdekin, M A., "Initiation of Brittle Fracture in Structural Steels," The British Welding Journal, Vol 14, No 12, 1967, pp 649-659 Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized W F Franz Development of a Pendulum-Type Dynamic Tear-Test Machine REFERENCE: Franz, W F., "Development of a P e n d u l u m - T y p e D y n a m i c Tear-Test Machine," Impact Testing of Metals, ASTM STP 466, American Society for Testing and Materials, 1970, pp 303-313 ABSTRACT: New American Petroleum Institute specifications for linepipe steels has prompted an evaluation of testing machines available to perform the Battelle drop-weight tear test (DWTT) This evaluation indicated a need for a machine of new design that would be safe, accurate, require little maintenance, and be acceptable as an industry-wide standard The machine preferred was the pendulum-type machine rather than a vertical drop-weight type because of low maintenance, operator comfort, and accuracy of fracture-energy determination Therefore, a pendulum-type machine was designed and built by the U.S Steel Applied Research Laboratory This new machine has a 6300-ft.lb capacity and is capable of testing both the Battelle 12-in.-long D W T T specimen for line*pipe steels and the Naval Research Laboratory 18-in.-long dynamic-tear-test specimen for ship-plate steels The pendulum head and anvil are designed to prevent interference between the broken sections of the test specimen and the pendulum after impact The frame structure is designed to prevent vibration within the structure The machine is operated by compressed air-mechanical devices, and the control circuit is designed to provide fail-safe operation by one man Performance testing, strain analysis, and high-speed photography indicate that this machine fulfills the desired design goals In the interest of standardization, the design is being proposed for industry-wide use KEY WORDS: design, pendulum, dynamic tests, drop-weight tests, tear tests, machine, line pipe, ship plates, steels, fracture toughness, fracture energy, evaluation, tests T h e d y n a m i c t e a r t e s t has b e e n a d v o c a t e d for m a n y y e a r s as a m e a n s of i n d i c a t i n g t h e f r a c t u r e p r o p a g a t i o n c h a r a c t e r i s t i c s of steel T h e N a v a l R e s e a r c h L a b o r a t o r y ( N R L ) is n o t e d e s p e c i a l l y for its w o r k in t h i s field A s t h e r e s u l t of N R L r e c o m m e n d a t i o n s a n d a r e s e a r c h p r o g r a m ~ s p o n sored by the American Gas Association at the Battelle Memorial Instit u t e , t h e d r o p - w e i g h t t e a r t e s t ( D W T T ) is b e i n g used to i n d i c a t e t h e Section supervisor, Applied Research Laboratory, U.S Steel Corp., Monroeville, Pa 15146 Pipe Line Research Committee of American Gas Association, Symposium on Line Pipe Research, Dallas, Tex., 17, 18 Nov 1965 Copyright by ASTM Int'l (all rights reserved); Sat Dec303 09:47:03 EST 2015 Downloaded/printed Copyright 1970 bybyASTM International www.aslm.org University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 304 IMPACTTESTING OF METALS STRIKEROF TESTINGMACHINE ~ //= ~ ) Is" ~z / WELD,N ,/16" SLOT ~ 8" ~i: 8" II TiTAN,UM ':~'.' =-t CROSSSECTIONOFNOTCH FIG Naval Research Laboratory dynamic tear-test specimen for ship plate steel ~racture toughness and related transition temperature of line-pipe steels The American Petroleum Institute (API) recently has included supplementary requirements for the use of the DWTT in revised specifications for line pipe 3.~ Because of these new specifications, it will be necessary to equip pipe manufacturing plants with machines for conducting the Battelle DWTT Other plants, however, may be required to perform an NRL dynamic tear test for ship-plate steels Although the NRL specimen, Fig 1, is larger than the DWTT specimen, Fig 2, the NRL test can be made on the same type of machine as that required for the DWTT specimen Because of the need for many new testing machines to perform these tests, the Applied Research Laboratory of the U.S Steel Corporation investigated the availability and the design of a machine for plant use that would be capable of testing both the Battelle and NRL specimens American Petroleum Institute Specification for Spiral-Weld Line Pipe, API Standard 5LS, 4th ed., March 1969 4American Petroleum Institute Specification for High-Test Line Pipe, API Standard 5LX, 16th ed., March 1969 STRIKEROF TESTINGMACHINE +0.0005" QO01" _0,0009" ROOTRADIUS PIPE WALL THICKNESS-~f ! DETAILOF PRESSEDNOTCH FIG Battelle drop-weight tear-test specimen for line-pipe steel Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized FRANZ ON A DYNAMIC TEAR-TEST MACHINE 305 Survey of Existing Machines The dynamic tear test of the Battelle and NRL specimens may be performed on either a vertical drop-weight machine or a pendulum-type machine Although the pendulum-type machine has a larger initial cost, it is preferred because of lower maintenance costs, relative noise level, and accuracy of fracture-energy determination The foundation of a vertical machine must absorb the full impact of the falling weight for each test, and maintenance can become a problem Also, the noise level associated with a vertical machine, especially with machines of higher capacities, can present personnel problems The first large pendulum-type dynamic tear-test machine was built by the NRL in 1963 This was an experimental machine that served its FIG Naval Research Laboratory type penautum aynamw tear-test machine at U.S Steel Applied Research Laboratory Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 306 IMPACT TESTING OF METALS purpose well but did not have many of the refinements believed to be required of a machine for plant use Other pendulum-type machines have since been built that are either duplicates or modifications of the NRL machine A near duplicate of the NRL machine, Fig 3, was obtained by the U.S Steel Research Laboratory, and this machine was used to assist in determining what refinements should be made Design of New Machine General Design The criteria for the new design were safety, accuracy of fracture~ energy determination, and economy of construction and maintenance An assembly of the new machine design is shown in Fig Experience and knowledge gained in years past with Chaxpy notched-bar impact machines were helpful in considering the design for this machine Rigidity of anvil and frame axe important It was believed desirable to isolate the foundation of the anvil from the foundation of the frame structure With this arrangement, the shock of impact on the anvil is prevented from feeding back to the frame, where undesirable vibrations can influence fracture-energy determination The frame is a simple and clean design without tripping hazards or other obstructions It is of rigid construction to keep deflections caused by the centrifugal force of the swinging pendulum to a negligible amount The frame is free of impact loads because the specimen is struck at the center of percussion of the pendulum, and the frame is isolated from the anvil Capacity Much consideration was given to the capacity of the new machine Because the machine was being designed to test two types of specimens, the evaluation of capacity for the machine was based on present and future steels that would be available in these types of specimens NRL personnel were consulted, and it was concluded that a capacity of 6000 ft'lb would be adequate The possibility of using two pendulums of different capacities was not considered desirable for a plant machine because of changeover problems and the desire for standardization The final design has a capacity of 6300 ft-lb Pendulum A major criterion in the design of a pendulum head is the ability of the pendulum to swing free after impact without interference by the broken sections of the test specimen This is especially critical with the Battelle DWTT specimen because the side clearance between the anvil and tup is only ~ in compared with a specimen width of in Because the broken Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions "*4 Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized FIG New U.S Steel pendulum-type dynamic tear-test machine 308 IMPACT TESTING OF METALS specimen sections usually are horizontal after impact, the side clearance amounts to only 1/~ in The use of a U or straddle-type head was considered to offer the best solution to this problem The weight of the pendulum head is distributed so that the center of percussion is located at the center of the vertical height of the tup or striker surface By striking the specimen at this location on the pendulum, there is no reaction at the pivot shaft, which in this case is the instantaneous axis of rotation of the compound pendulum Theoretically, in the ideal pendulum the center of mass would be at the center of percussion, but, since this is not practical, the weight of the parts outside the pendulum head were kept to a minimum For this reason, the pendulum arm is made of 5~-in outside diameter by 8//16-in wall cold-drawn mechanical tubing A disk brake is used to keep the weight of the brake drum to a minimum Self-aligning, heavy-duty ball bearings are used to minimize friction losses The energy required to break the specimen is determined from the residual swing, or angle of elevation, of the pendulum after the specimen is broken A conventional pointer with a spring-loaded friction pad and an angle-indicator dial are used to obtain the angle of elevation of the pendulum A critical part of the pendulum-head design is the method of attaching the tup (specimen striker) to the pendulum One possible method is to use a solid forging for the cross member of the pendulum head, and to machine the tup and cross member out of the forging In the pilot machine, however, a two-piece welded design was adopted The configuration of the tup and the method of fitting and attaching it to the cross member are illustrated in Fig The elongated tongue on the front of the tup was used to eliminate the need for a weld and to reduce the stress concentration at the top corner, where a ~ in radius is used The tup and the horizontal cross member of the pendulum head are made of HY-80 steel to obtain high impact strength after welding A hardened replaceable cap is used on the tup surface The pendulum assembly is calibrated in accordance with ASTM Standard for Notched Bar Impact Testing of Metallic Materials (E 23-66) Anvil The anvil is designed to accommodate either the Battelle D W T T specimen or the NRL specimen, Fig The photograph shows the anvil with a Battelle D W T T specimen The anvil is adjusted to accommodate the NRL specimen by moving the anvil blocks back and to the outside position The keyways are cut so as to properly position the anvil blocks The anvil block is keyed to the base plate to eliminate the shearing forces on the hold-down bolts The anvil blocks and specimen deflectors are designed to minimize the possibility of contact between the broken Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions FRANZ ON A DYNAMIC TEAR-TEST MACHINE 309 A CROSS MEMBEROF PENDULUM HEAD~ A ~ / \ AS SHOWN, ON BOTH SIDES SECTION A-A FIG Method of fitting and attaching tup to pendulum head FIG Anvil of new machine at U.S ~teel Applied Research Laboratory with a Battelle D W T T specimen Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 310 IMPACT TESTING OF METALS sections of the test specimen and the pendulum head, and to safely guide the broken sections away from the operator Adjustable, hardened replaceable caps are used at the points of contact with the specimen These caps can be turned end to end to double their life The specimensupport blocks can be shimmed so as to locate test specimens of various thicknesses at the center of percussion of the pendulum The anvil is embedded rigidly in a concrete base that is isolated from the concrete-base pads for the frame structure, and vertically embedded H-beams are used to constrain the anvil from horizontal motion Safety Latches Two safety latches are used, one under each side of the elevated pendulum They are spring-loaded in the safe position so that failure of the air supply will not create a hazardous condition When the pendulum is raised, the safety latches are moved automatically out of the path of the pendulum Hoist, Release Mechanism, and Control Circuit A commercially available air-operated hoist is used to lift the pendulum An air hoist was selected because it has a faster lifting rate than that obtainable with electric4ype hoists The entire machine is operated by compressed air, and no electricity is required The hoist chain is lowered by a momentary depression of the "down" valve button, and movement of the chain will stop automatically when the chain is long enough to be attached to the pendulum After the chain is attached to the pendulum, the pendulum is raised by continually depressing the "up" valve button The pendulum will continue to rise until a ball stop on the chain contacts a lever on the hoist Adjustment of the pendulum height to obtain proper energy capacity for the machine is made by moving the location of the ball on the hoist chain Because there are no dangling release cables, the operator has no concern about cables catching onto the structure The release mechanism is air-operated and cannot be accidentally released while the pendulum is being raised The release mechanism will not operate by depressing the "test" button First, the "safety-out" button must be continuously depressed, and then the "test" button must be depressed to release the pendulum This procedure not only requires both hands of the operator, but also prevents the pendulum from being dropped accidentally on the safety latches, which would require the operator to climb a ladder to reattach the pendulum The damping brake valve is foot-operated and is readily accessible to the operator when he is ready to perform the test (that is, he is in the test position) The control circuit is designed to be failsafe for operation by one man Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions author FRANZ ON A DYNAMIC TEAR-TEST MACHINE Performance 311 Tests The new pendulum-type dynamic tear-test machine has been installed at U.S Steel's Applied Research Laboratory, Fig Specimens made from special alloy steels were used to test the machine at maximum capacity During eight of these tests the pendulum was stopped completely without causing any apparent damage to the machine Two tests were with unnotched specimens that caused a reverse swing of the pendulum The results of all these tests did indicate, however, that the side weights on the pendulum should be keyed to the pendulum cross member to eliminate the shear force on the two 1-in bolts with which the side weights are attached FIG New pendulum-type dynamic tear-test machine at U.S Steel Applied Research Laboratory Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized 312 IMPACTTESTINGOF METALS FRONT "• BACK ~'~ & FIG Stress induced in pendulum while breaking Battelle DWTT specimen requiring 6150 ft.lb for fracture Electric-strain gages were used to determine the stresses induced at several locations on the pendulum and the frame The stress levels shown in Fig for the pendulum were induced in a test with a 1-in.-thick special-alloy Battelle specimen that required 6150 ft lb of energy for fracture A maximum longitudinal stress of 660 psi was measured in the bottom side of the slanted frame member at a point in line with the pendulum shaft during the free swing of 240 deg of the pendulum On the basis of the yield strengths of the steels used for these parts (minimum of 80,000 psi for the pendulum head, 65,000 psi for the pendulum arm, and 35,000 psi for the frame), the stresses induced are considered to be safe High-speed motion pictures were taken to determine whether the broken sections of the specimen were interfering with the free swing of the pendulum and to determine the effectiveness of the specimen deflectors and guards The breaking of both high- and low-energy Battelle specimens and high- and low-energy NRL specimens was photographed and analyzed In all tests the broken sections remained in a horizontal plane as they passed through the anvil throat The low-energy sections of both specimen types (less than 1000 ft.lb) either remained on the anvil or fell close to the frame of the anvil base The higher energy Battelle and NRL specimen sections fell in front of the anvil, and some sections even hit the plywood backstop, ft beyond the point of impact Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions au FRANZ ON A DYNAMIC TEAR-TEST MACHINE 313 The only specimen that had any contact with the tup of the pendulum after impact was the low-energy Battelle specimen With this specimen, the cleavage fracture was complete immediately after impact The broken sections then pivoted horizontally, and the trailing edge of the specimen sections touched the side of the tup as they passed through the throat of the anvil (The Battelle specimen has only a 1/~-in clearance at this point) It is doubtful that this contact with the tup dragged the pendulum a significant amount; however, to alleviate this problem, the sides of the tup have been tapered back and rounded at the back edge Motion pictures of additional tests indicated that the tup modification eliminated the contact with the broken sections Compared with the low-energy Battelle specimens, the higher-energy Battelle specimens required that the tup travel farther through the specimen before it broke into two pieces The tup and sections of the higher energy specimens pass through the throat of the anvil before the specimen sections pivot to a longitudinal position The longer NRL specimens have a 13/~-in clearance between the tup and the anvil, and neither the low- nor tile high-energy specimens have any contact with the striker after impact The high sides of the anvil blocks deflect the specimen sections into a forward position and are effective in constraining the direction of travel of the broken sections R e c o m m e n d a t i o n s for Standardization Experience concerning standardization problems with Charpy impact machines indicates that it would be desirable to standardize on a pendulum-type dynamic tear-test machine on an industry-wide basis To further this aim, the machine at the Laboratory has been demonstrated to interested personnel, and detail drawings of the machine have been made available to pipe manufacturers and users Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorize STP466-EB/Mar 1970 General Discussion C E Turner (written d i s c u s s i o n ) - - I n discussing the determination of fracture toughness by impact testing the role of strain rate is clearly of prime importance For high-strength steels, aluminium alloys and mild steels above the ductile-brittle transition the energy absorbed in Charpy and slow-bend tests of the same size of test piece is broadly similar I t commonly is accepted that for low-strength steels below the ductilebrittle transition temperature, impact seems a more critical condition than static loading The relative difficulty of starting a brittle crack and ease of propagating it in mild steel was well shown in the Robertson test and has been expressed quantitatively by Eftis and Krafft in their presentation s of K ~ as a function of ~ This picture seems to have been accepted generally though with little direct confirmation The dynamic toughness values that have been reported for low-strength steels up to about in thick, in the transition temperature range, (for example, footnotes 2-5) have been low One design philosophy proposes reliance on avoidance of initiation, perhaps measured by crack opening displacement (COD) (footnotes 6, 7) rather than control of propagation or arrest The'choice of design philosophy for fracture rate effects is complicated by the role of mechanical and metallurgical damage (for example, strain aging) which appears to destroy the high resistance normally found to static initiation, thus allowing a crack to "jump in" and propagate dynamically, as for example in the original Wells-British Welding Research Association wide plate test Current studies, however, notably the Heavy-Section Steel Reader in mechanical engineering, Mechanical Engineering Department, Imperial College, London, England 2Eftis, J and Krafft, J M., "A Comparison of the Initiation with the Rapid Propagation of a Crack in a Mild Steel Plate," Transactions, American Society of Mechanical Engineers, Vol 87D, 1965, p 257 a Crosley, P B and Ripling, E J., "Dynamic Fracture Toughness of A533 Steel," American Welding Society/American Society of Mechanical Engineers Conference, Chicago, April 1968 Radon, J C and Turner, C E., "Fracture Toughness Measurements by Instrumented Impact Test," Engineering Fracture Mechanics, Vol I, 1969, p 411 s Turner, C E and Radon, J C., "Fracture Toughness Measurements on Low Strength Structural Steels," ~nd International Conference for Fracture, Brighton, April 1969 e Nichols, R W., "The Use of Critical Crack Opening Displacement Techniques for the Selection of Fracture Resistant Materials," Symposium on Fracture Toughness Concepts for Weldable Structural Steel, Culcheth, April 1969 Wells, A A., "The Specification of Permissible Defect Sizes in Welded Metal Structures," ~nd International Conference on Fracture, Brighton, April 1969 Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 314 EST 2015 Downloaded/printed Copyright9 1970by by ASTM International www.aslm.org University of Washington (University of Washington) pursuant to License Agreement No further reproductions authorized GENERAL DISCUSSION 315 Technology (HSST) program and related work in USA suggest further complicating aspects of thickness, stretch zone, and rate spectrum effects that give rise to doubt whether the above picture is complete It may be asked also whether we should attempt to characterize parent material by selecting a numerical value of toughness, be it Charpy or some other measure, adjusted to provide an umbrella under which all uncertainties shelter and by which we hope to be safeguarded, or whether for each effect such as strain rate, metallurgical damage from weldments, and even thickness, separate tests should be made to get a value of toughness realistic for each and every circumstance The answer will depend on whether we are discussing tests for design purposes or for quality control However, in the past C~ values have been based on the "umbrella" philosophy by empirical correlations of parent plate tests directly with real or simulated service behavior Fracture mechanics concepts tend to be based on the philosophy of studying the worst case This difference of viewpoint must not be overlooked in trying to relate the two approaches, nor indeed when conducting Charpy or similar tests on local regions of "damaged" material The acceptable toughness levels aimed at by the umbrella and "worst case" philosophies, whether by a temperature criteria, energy level, or other measure, must be surely quite different, this difference reflecting the importance of the factors that are being covered by the current umbrella type Charpy values Copyright by ASTM Int'l (all rights reserved); Sat Dec 09:47:03 EST 2015 Downloaded/printed by University of Washington (University of Washington) pursuant to License Agreement No further reproductions autho