1、 SURFACE VEHICLE STANDARD J2575 APR2015 Issued 2004-06 Reaffirmed 2015-04 Superseding J2575 JUN2004 Standardized Dent Resistance Test Procedure RATIONALE J2575 has been reaffirmed to comply with the SAE five-year review policy. _ SAE Technical Standards Board Rules provide that: “This report is publ
2、ished by SAE to advance the state of technical and engineering sciences. The use of this report is entirely voluntary, and its applicability and suitability for any particular use, including any patent infringement arising therefrom, is the sole responsibility of the user.” SAE reviews each technica
3、l report at least every five years at which time it may be revised, reaffirmed, stabilized, or cancelled. SAE invites your written comments and suggestions. Copyright 2015 SAE International All rights reserved. No part of this publication may be reproduced, stored in a retrieval system or transmitte
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5、ADDRESS: http:/www.sae.org SAE values your input. To provide feedback on this Technical Report, please visit http:/www.sae.org/technical/standards/J2575_201504 1. Scope These test procedures were developed based upon the knowledge that steel panel dent resistance characteristics are strain rate depe
6、ndent. The “quasi-static” section of the procedure simulates real world dent phenomena that occur at low indenter velocities such as palm-printing, elbow marks, plant handling, etc. The indenter velocity specified in this section of the procedure is set to minimize material strain rate effects. The
7、dynamic section of the procedure simulates loading conditions that occur at higher indenter velocities, such as hail impact, shopping carts, and door-to-door parking lot impact. Three dent test schedules are addressed in this procedure. Schedule A is for use with a specified laboratory prepared (gen
8、eric) panel, Schedule B is for use with a formed automotive outer body panel or assembly, and Schedule C addresses end product or full vehicle testing. These schedules are targeted at sheet steel samples obtained at different points in an auto/steel product development cycle. A multiple schedule app
9、roach has been utilized to maximize dent test method flexibility and thereby allow both the steel producers and end users to benefit from a standardized approach. Extrapolating results from one schedule to another, however, may not be valid and could result in erroneous conclusions. For “quasi-stati
10、c” testing, each test schedule provides a load-displacement curve for a given material, either as-stamped or after assembly, under a prescribed set of conditions such as specified strain state, specimen geometry, boundary conditions, indenter type, etc. In order to obtain the most information about
11、dynamic denting behavior comparable in scope to the quasi-static testing, it is necessary to use high speed measuring and recording equipment. If use of this equipment is cost-prohibitive, other dynamic dent evaluations use a drop weight, pendulum, or air gun to fire a projectile at the test surface
12、. For this latter type of dynamic testing, only the impact energy is calculated and the dent depth measured after impact. This information may be sufficient to measure some aspects of dent resistance in the absence of high-speed measuring and recording equipment, but the indenter speed/energy intera
13、ction will not be captured. Uniform methods for calculating panel property characteristics such as stiffness and oil canning load are presented. A format for reporting test results is suggested. Using this procedure, reproducible values of “dent resistance” should be obtained in different laboratori
14、es. 1.1 Purpose The test methods and definitions presented in this procedure are for the mechanical dent testing of sheet steel products. Both quasi-static (low velocity) and dynamic (higher velocity) indenting conditions are discussed. The objective of these methods is to provide reproducible and c
15、omparable dent test results. 2. References 2.1.1 OTHER PUBLICATIONS 1. Report on Steel Body Panel Performance Characteristics, vols. 1 DT = Displacement transducer; NCSC = Non-contact surface contour Mechanical Properties Initial (flat) blank Formed Orientation with respect to rolling or stamping di
16、rection longitudinal longitudinal Gauge (in) 0.031 0.028 Surface Strain (%, major x minor) N/A 2.3 x 2.1 Yield Strength (ksi) 31.2 49.7 Tensile Strength (ksi) 52.6 55.6 Total Elongation (%) 36.5 22.4 Uniform Elongation (%) 20.7 5.6 Yield Point Elongation (%) 0.0 0.0 Normal Plastic Anisotropy (R-Valu
17、e) 1.97 n/a Strain Hardening Exponent (n-Value) 0.207 n/a n-Value Determination (e.g., full curve, 10%-20%, etc.) 10% to unif. elong. n/a Strength Coefficient K-Value (ksi) 97.1 n/a Painting Information Production paint cycle or spray painted? production paint cycle Paint Color white Material layers
18、 on top of steel surface electrozinc, phosphate, electrodeposited primer (ELPO), white basecoat paint, clear topcoat _ SAE INTERNATIONAL J2575 Reaffirmed APR2015 15 of 465. Dynamic Dent Evaluations: General Requirements and Test Procedure 5.1 Discussion of Dynamic Indenting Conditions There are only
19、 limited dent evaluation facilities in existence that have the capability of recording the entire load-displacement cycle during a dynamic impact occurring at velocities greater than 2 miles per hour. As a result, most locations interested in dynamic dent evaluations will use a drop weight, pendulum
20、, or air gun to fire a projectile at the test surface. Although this type of testing does not facilitate measuring and recording the complete load-displacement cycle, the impacting energy is known or can be calculated, and it is possible to measure the dent depth after impact. It is known that sheet
21、 steels are strain rate sensitive and the strength of sheet steels increases when the deformation rate increases. Therefore, the dent resistance of sheet steels depends upon the indenting speed used in the test. The same amount of energy generated at different indenting speeds would result in differ
22、ent dent depths. In order to minimize the strain rate effect during dent tests, a constant speed should be maintained when the purpose of dent tests is not to study the dent testing speed effect. Although dynamic denting characteristics may be evaluated using either a simple drop weight test or a hy
23、draulically controlled test machine coupled with a high speed data acquisition system recording load and displacement data, it is important to distinguish differences between the two approaches. The energy generated in the drop-weight test or the air gun type of test is kinematic energy which depend
24、s upon the velocity and indenter mass. Usually, different amounts of energy are achieved (through changes in the indenter velocity) by varying the drop heights in the drop weight test or varying the air-pressures in the air-gun test. When the drop-weight test or the air-gun test is used for the eval
25、uation of dent resistance, it is recommended that different indenter masses be used to achieve different amounts of energy instead of the drop heights or air pressures in order to minimize the speed effect mentioned above. In hydraulically controlled test machines, the applied energy is calculated f
26、rom the area under the load-displacement curve, with the applied load directly relating to the deformation work involved in making the dent. In drop-weight and air gun tests, much of the applied energy is converted to the deformation work that causes a dent in the test specimen. However, a percentag
27、e of the applied energy in drop-weight or air gun tests is also dissipated as heat. Unless the portion of the impact energy that contributes to deformation work can be isolated, users of dynamic dent test data are cautioned against doing a direct comparison of results obtained from different test me
28、thods. 5.2 General Requirements for Dynamic Denting 5.2.1 TEST FRAME See 4.2.1. _ SAE INTERNATIONAL J2575 Reaffirmed APR2015 16 of 465.2.2 TEST ACTUATOR 5.2.2.1 Testing on Equipment Which Can Measure and Record Complete Load-Displacement Loading and Unloading Cycle See 4.2.2. 5.2.2.2 Testing on Equi
29、pment Which Can Measure and Record Only Impacting Energy and Final Dent Depth Not applicable. 5.2.3 SYSTEM STIFFNESS The system must be sufficiently rigid to minimize deflection at a load of 222 N (50 lbf). Round robin testing of generic experimental panels under quasi-static conditions using frames
30、 with stiffness values ranging from 1.23 N/m x 106 N/m (7 lbf/in x 103 lbf/in) to more than 1.75 N/m x 107 N/m (1 lbf/in x 105 lbf/in) produced satisfactory results. If the test frame stiffness is suspect, then an external reference point must be used for panel deflection measurements. 5.2.4 INDENTE
31、R DESCRIPTION 5.2.4.1 Testing on Equipment Which Can Measure and Record Complete Load-Displacement Loading and Unloading Cycle A Type I hard indenter (see 4.2.4.1) may be considered typical. Alternative indenter shapes may also be used to address specific real-world denting phenomena. 5.2.4.2 Testin
32、g on Equipment Which Can Measure and Record Only Impacting Energy and Final Dent Depth Alternative (shape, material, and mass) indenters may be used to generate different energy levels for a drop weight, pendulum, or air gun type test. 5.2.5 SPEED OF TESTING 5.2.5.1 Testing on Equipment Which Can Me
33、asure and Record Complete Load-Displacement Loading and Unloading Cycle A constant actuator speed greater than 894 mm 90 mm per second (2 mile/hour or 35.2 in 3 inper second ) will be used during both the loading and unloading portions of the test and will be recorded. _ SAE INTERNATIONAL J2575 Reaf
34、firmed APR2015 17 of 465.2.5.2 Testing on Equipment Which Can Measure and Record Only Impacting Energy and Final Dent Depth The impacting energies within a given sequence should encompass both the low and high energy levels that are of interest to the user (see 5.3.2, Note 1). 5.2.6 SYSTEM PERFORMAN
35、CE 5.2.6.1 Testing on Equipment Which Can Measure and Record Complete Load-Displacement Loading and Unloading Cycle See 4.2.6. 5.2.6.2 Testing on Equipment Which Can Measure and Record Only Impacting Energy and Final Dent Depth The angle of load input to the panel shall be perpendicular to the surfa
36、ce at the point of first contact within 2.5 degrees, and continue on this angle throughout the test without shifting or skidding along the surface of the panel. 5.2.7 DISPLACEMENT TRANSDUCER 5.2.7.1 Testing on Equipment Which Can Measure and Record Complete Load-Displacement Loading and Unloading Cy
37、cle See 4.2.8. 5.2.7.2 Testing on Equipment Which Can Measure and Record Only Impacting Energy and Final Dent Depth The displacement transducer used to measure dent depth shall have a resolution of 0.013 mm (0.0005 in) or better. 5.2.8 CALIBRATION See 4.2.9. 5.2.9 ADDITIONAL HARDWARE REQUIRED 5.2.9.
38、1 Testing on Equipment Which Can Measure and Record Complete Load-Displacement Loading and Unloading Cycle See 4.2.10. _ SAE INTERNATIONAL J2575 Reaffirmed APR2015 18 of 465.2.9.2 Testing on Equipment Which Can Measure and Record Only Impacting Energy and Final Dent Depth Not applicable. 5.3 General
39、 Test Procedure - Dynamic Dent Testing 5.3.1 TESTING ON EQUIPMENT WHICH CAN MEASURE AND RECORD COMPLETE LOAD-DISPLACEMENT LOADING AND UNLOADING CYCLE: TEST SEQUENCE (SEE ALSO FIGURE 2) 1. Calibrate testing system as required (see 5.2.8). 2. Mount test specimen (e.g., body panel) in test frame. 3. Ma
40、rk test location on test specimen. 4. Wipe the test location using a clean cloth to remove any extraneous dirt from the test location. 5. Align actuator normal to surface at test location (see 6.1.6). 6. Apply a preload to 7 N (1.57 lbf) and record the load-displacement history. This loading sequenc
41、e establishes the displacement, which is the reference value from which all other displacement readings are determined. Unload back to zero N (0 lbf). 7. Record load versus displacement history as sample is indented with 0.2 J (1.77 in-lbf) impact energy at a constant speed and retracted back to zer
42、o J. 8. Apply a post load to 7 N (1.57 lbf) at a speed of 50.4 mm (2 in) per minute and record load-displacement history. Unload back to zero N (0 lbf). 9. Record load versus displacement history as sample is indented with 0.3 J (2.66 in-lbf) impact energy at a constant speed and retracted back to z
43、ero J. 10. Apply a post load to 7 N (1.57 lbf) at a speed of 50.4 mm (2 in) per minute and record load-displacement history. Unload back to zero N (0 lbf). 11. Record load versus displacement history as sample is indented with 0.4 J (3.54 in-lbf) impact energy at a constant speed and retracted back
44、to zero J. 12. Apply a post load to 7 N (1.57 lbf) at a speed of 50.4 mm (2 in) per minute and record load-displacement history. Unload back to zero N (0 lbf). 13. Record load versus displacement history as sample is indented with 0.5 J (4.43 in-lbf) impact energy at a constant speed and retracted b
45、ack to zero J. 14. Apply a post load to 7 N (1.57 lbf) at a speed of 50.4 mm (2 in) per minute and record load-displacement history. Unload back to zero N (0 lbf). NOTE 1This indenting sequence listed (0.2, 0.3, 0.4, and 0.5 J) is only a suggestion. The impacting energies within a given sequence sho
46、uld encompass both the low and high energy levels that are of interest to the user. NOTE 2If it is desired and possible with the equipment in use, a displacement sequence (i.e., impacting until 2.5, 5.0, 7.5, and 10.0 mm 0.10 in, 0.20 in, 0.30 in, and 0.39 in maximum displacements) may be used inste
47、ad of an energy sequence. NOTE 3If the dent depth after one specific energy increment is desired, a single impact cycle is sufficient providing a preload and post load are also used to determine dent depth. A slow speed must be used in pre- and post-loading to avoid dynamic effects. NOTE 4The effects of a painted rather than an unpainted sample surface on the test results are not known. In addition, the effect of the paint thickness on the test results is not known. However, there are cases where a painted surface is desired (see 4.5.2.1). _ SAE I
