This document specifies a method for assessing the resilience of sheet metal and thin strip in a flat strain bending deformation method. Plane strain bending is a typical deformation method for stamped formed parts, which can exhibit significant rebound. The application of this method allows an accurate and quantitative assessment of the amount of bending rebound. This document is suitable for material characterisation, forming process control, tool design and finite element program calibration for sheet metal and thin strip rebound control requirements.
2 Normative references
The contents of the following documents constitute essential provisions of this document by means of normative references in the text. Where a reference is dated, only the version corresponding to that date is applicable to this document; where a reference is not dated, the latest version (including all revision sheets) is applicable to this document.
GB/T 8170 numerical modification rules and limit values of the representation and determination
3 Terminology and definitions
The following terms and definitions apply to this document.
3.1
Curvature curvaturer
The reciprocal of the radius of curvature measured along the longitudinal direction in the middle of the inner surface of a drawn and bent specimen. Note:See equation (1).
4 Symbols and descriptions
The symbols and descriptions used in this document are shown in Table 1.
5 Principle
The test uses the pull-bend method to assess the resilience of thin metal sheets and strips. The amount of resilience is determined by measuring the relative change in curvature when the specimen is loaded and after unloading (see 3.1 and 3.2). The nominal tensile stress acting on the specimen is determined using the measured values of punch stroke and punch pressure (see Appendix B).
6 Test equipment
6.1 Bending test apparatus for rebound assessment
An example of the bending test apparatus used in the test is shown in Figure 2. The radius of the semi-cylindrical punch should be (100 ± 1) mm. the radius and dimensional tolerances can be determined by agreement between the parties concerned.
6.2 Device for measuring the radius of curvature of the specimen
The principle of radius of curvature measurement is shown in Appendix C. The gauges used should have a resolution of 0.001 mm. optical micrometers and other non-contact measuring probes can also be used.
7 Specimens
The specimens to be used for the test shall be as follows:
a) shall be rectangular in length (500sh10) mm and width (50sh1) mm;
b) The thickness shall be the original thickness of the sheet or strip;
c) shall be cut parallel or perpendicular to the direction of rolling as agreed by the parties concerned; and
d) The edges shall be shear edges; unless otherwise specified or caused by shear, the specimen shall be free from unnecessary alteration or heat; e) The surface shall be free from defects, such as scratches, which may affect the test results.
8 Test procedure
The test shall follow the following procedure.
a) Test temperature: Normally the test is carried out at an ambient temperature of 10 °C to 35 °C. If necessary, the temperature should be recorded. For tests with strict temperature
Requirements of the test, should be in the (23 Shi 5) ℃ range.
b) Bending test: the specimen should be placed on the crimping die (see Figure 2), and then apply crimping force to the specimen, in accordance with Appendix A to calculate the unit area
Crimping force, the maximum unit area crimping force should be in the range of 2% to 3% of the tensile strength of the test material. The punch is moved until the punch stroke (h) reaches a predetermined value. The size of the punch stroke shall be determined so that the angle of spread of the specimen along the punch (28) is not less than 120° (see Figure B.1) and the lubricant shall be determined by agreement between the parties concerned. The friction between the specimen and the punch should be as low as possible, with a coefficient of friction of less than 0.05, so that the nominal tensile stress is evenly distributed throughout the specimen on the punch. It is recommended that polymeric films and oils are used as lubricants for the press surfaces. When using polymeric film lubrication, a new one should be used for each test. The punch stroke (h) and the punch pressure (FP) should be measured using displacement gauges and force transducers respectively. Displacement gauges for punch stroke measurement and force transducers for punch pressure measurement should have a resolving power of less than 0.5 mm and 100 N respectively.
c) Calculation of the nominal tensile stress; this shall be calculated in accordance with Appendix B.
d) Determination of radius of curvature and rebound calculation: the radius of curvature (r') of the inner surface of the specimen after unloading shall be determined in accordance with the provisions of Appendix C using a gauge in the
Bending specimens along the middle of the longitudinal determination. The radius of curvature (r) of the inner surface of the specimen when loaded shall be the radius of the top of the punch. The amount of rebound (z) is calculated using formula (2). The recommended width (w) of the gauge base for measuring the curvature of the specimen after unloading is 20 mm (see Appendix C). This is based on the observation from previous tests that the curvature of the specimen after rebound is almost uniform in the middle 20 mm of the specimen. e) Modification: The measured data should be modified according to GB/T 8170.
Note: Three valid digits are retained.
9 Test report
If a test report is required, the items to be included in the report shall be determined by agreement between the parties concerned and shall be selected from the following:
a) Number of this document
b) Test conditions: punch radius, punch stroke, lubricant, type and thickness of polymeric film, punching force, crimping force per unit area, direction of interception of the specimen in relation to the direction of rolling of the material;
c) test results; nominal tensile stress, rebound; and
d) Type, thickness, grade and condition of the test material.
e) assessment of measurement uncertainty (or precision and deviation).
Appendix A (normative) Calculation of crimping force per unit area
Appendix B (normative) Method of calculating nominal tensile stress
Appendix c (normative) Apparatus for measuring radius of curvature
1 Scope 2 Normative references 3 Terminology and definitions 4 Symbols and descriptions 5 Principle 6 Test equipment 7 Specimens 8 Test procedure 9 Test report Appendix A (normative) Calculation of crimping force per unit area Appendix B (normative) Method of calculating nominal tensile stress Appendix c (normative) Apparatus for measuring radius of curvature
1 Scope
This document specifies a method for assessing the resilience of sheet metal and thin strip in a flat strain bending deformation method. Plane strain bending is a typical deformation method for stamped formed parts, which can exhibit significant rebound. The application of this method allows an accurate and quantitative assessment of the amount of bending rebound. This document is suitable for material characterisation, forming process control, tool design and finite element program calibration for sheet metal and thin strip rebound control requirements.
2 Normative references
The contents of the following documents constitute essential provisions of this document by means of normative references in the text. Where a reference is dated, only the version corresponding to that date is applicable to this document; where a reference is not dated, the latest version (including all revision sheets) is applicable to this document.
GB/T 8170 numerical modification rules and limit values of the representation and determination
3 Terminology and definitions
The following terms and definitions apply to this document.
3.1
Curvature curvaturer
The reciprocal of the radius of curvature measured along the longitudinal direction in the middle of the inner surface of a drawn and bent specimen. Note:See equation (1).
4 Symbols and descriptions
The symbols and descriptions used in this document are shown in Table 1.
5 Principle
The test uses the pull-bend method to assess the resilience of thin metal sheets and strips. The amount of resilience is determined by measuring the relative change in curvature when the specimen is loaded and after unloading (see 3.1 and 3.2). The nominal tensile stress acting on the specimen is determined using the measured values of punch stroke and punch pressure (see Appendix B).
6 Test equipment
6.1 Bending test apparatus for rebound assessment
An example of the bending test apparatus used in the test is shown in Figure 2. The radius of the semi-cylindrical punch should be (100 ± 1) mm. the radius and dimensional tolerances can be determined by agreement between the parties concerned.
6.2 Device for measuring the radius of curvature of the specimen
The principle of radius of curvature measurement is shown in Appendix C. The gauges used should have a resolution of 0.001 mm. optical micrometers and other non-contact measuring probes can also be used.
7 Specimens
The specimens to be used for the test shall be as follows:
a) shall be rectangular in length (500sh10) mm and width (50sh1) mm;
b) The thickness shall be the original thickness of the sheet or strip;
c) shall be cut parallel or perpendicular to the direction of rolling as agreed by the parties concerned; and
d) The edges shall be shear edges; unless otherwise specified or caused by shear, the specimen shall be free from unnecessary alteration or heat; e) The surface shall be free from defects, such as scratches, which may affect the test results.
8 Test procedure
The test shall follow the following procedure.
a) Test temperature: Normally the test is carried out at an ambient temperature of 10 °C to 35 °C. If necessary, the temperature should be recorded. For tests with strict temperature
Requirements of the test, should be in the (23 Shi 5) ℃ range.
b) Bending test: the specimen should be placed on the crimping die (see Figure 2), and then apply crimping force to the specimen, in accordance with Appendix A to calculate the unit area
Crimping force, the maximum unit area crimping force should be in the range of 2% to 3% of the tensile strength of the test material. The punch is moved until the punch stroke (h) reaches a predetermined value. The size of the punch stroke shall be determined so that the angle of spread of the specimen along the punch (28) is not less than 120° (see Figure B.1) and the lubricant shall be determined by agreement between the parties concerned. The friction between the specimen and the punch should be as low as possible, with a coefficient of friction of less than 0.05, so that the nominal tensile stress is evenly distributed throughout the specimen on the punch. It is recommended that polymeric films and oils are used as lubricants for the press surfaces. When using polymeric film lubrication, a new one should be used for each test. The punch stroke (h) and the punch pressure (FP) should be measured using displacement gauges and force transducers respectively. Displacement gauges for punch stroke measurement and force transducers for punch pressure measurement should have a resolving power of less than 0.5 mm and 100 N respectively.
c) Calculation of the nominal tensile stress; this shall be calculated in accordance with Appendix B.
d) Determination of radius of curvature and rebound calculation: the radius of curvature (r') of the inner surface of the specimen after unloading shall be determined in accordance with the provisions of Appendix C using a gauge in the
Bending specimens along the middle of the longitudinal determination. The radius of curvature (r) of the inner surface of the specimen when loaded shall be the radius of the top of the punch. The amount of rebound (z) is calculated using formula (2). The recommended width (w) of the gauge base for measuring the curvature of the specimen after unloading is 20 mm (see Appendix C). This is based on the observation from previous tests that the curvature of the specimen after rebound is almost uniform in the middle 20 mm of the specimen. e) Modification: The measured data should be modified according to GB/T 8170.
Note: Three valid digits are retained.
9 Test report
If a test report is required, the items to be included in the report shall be determined by agreement between the parties concerned and shall be selected from the following:
a) Number of this document
b) Test conditions: punch radius, punch stroke, lubricant, type and thickness of polymeric film, punching force, crimping force per unit area, direction of interception of the specimen in relation to the direction of rolling of the material;
c) test results; nominal tensile stress, rebound; and
d) Type, thickness, grade and condition of the test material.
e) assessment of measurement uncertainty (or precision and deviation).
Appendix A (normative) Calculation of crimping force per unit area
Appendix B (normative) Method of calculating nominal tensile stress
Appendix c (normative) Apparatus for measuring radius of curvature
Contents of GB/T 22565.1-2021
1 Scope
2 Normative references
3 Terminology and definitions
4 Symbols and descriptions
5 Principle
6 Test equipment
7 Specimens
8 Test procedure
9 Test report
Appendix A (normative) Calculation of crimping force per unit area
Appendix B (normative) Method of calculating nominal tensile stress
Appendix c (normative) Apparatus for measuring radius of curvature
