Test method for measuring limit tip cold bending angle and equivalent fracture strain

A technology for determining limits and test methods, applied in the direction of using stable bending force to test the strength of materials, measuring devices, instruments, etc., can solve the problem of increasing the cost of test equipment, difficult to meet VDA238-100 technical standards, weakening the interpretability of results, etc. problems, to achieve the effect of reducing the cost of testing

CN114544383APending Publication Date: 2022-05-27武汉上善仿真科技有限责任公司
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Patent Information

Authority / Receiving Office
CN · China
Patent Type
Applications(China)
Current Assignee / Owner
Publication Date
2022-05-27

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Abstract

The invention discloses a test method for measuring a limit tip cold bending angle and equivalent fracture strain, which comprises the following steps: preparing a bending sample, setting an initial fixed loading stroke, determining existence and absence of a crack state, determining an effective sample, and measuring the limit cold bending angle. The method for measuring the equivalent fracture strain comprises the following steps: spraying speckles on the side surface of a sample, obtaining an effective sample for DIC data processing, calculating the deformation of the edge side of the effective sample, measuring the arc length and calculating the equivalent fracture strain. According to the invention, a technical scheme of combining fixed stroke loading, a DIC technology and theoretical calculation is adopted, and the limit cold bending angle and the equivalent fracture strain are accurately measured. According to the method, the failure moment of the material is accurately controlled, the intrinsic parameters of the material are measured, the test cost is reduced, and the method has important engineering practical significance and wide engineering application prospects.
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Description

Technical field

[0001] The present invention belongs to the field of mechanical properties testing of metal materials, in particular the test method involving the determination of the ultimate sharp cold bend angle and equivalent fracture strain of advanced high-strength steels. Background

[0002] With the continuous improvement of vehicle crash safety standards, in order to cope with the technical challenges brought by safety regulations, the proportion of advanced high-strength steels applied in the lightweight design of automotive bodies is increasing, especially the large number of hot stamped parts. However, in a car collision, for example, the bending deformation of A-column and B-pillar is a typical flat strain state failure under bending deformation, and the higher the material strength, the greater the risk of material failure. Therefore, the bendability of the material has become one of the key indicators to measure the mechanical properties of advanced high-strength s...

Examples

Embodiment 1

[0069] The present embodiment takes 1500MPa / 1.2mm of hot-formed steel bare plate as an example, using electron microscopy to assist observation to determine the crack state, the flowchart, such as Figure 1 The test flowchart for determining the ultimate sharp cold bend is shown, including the following steps:

[0070] Step 1: Prepare bending specimens: According to the specimen size requirements specified in the VDA238-100 technical standard, prepare a number of bending specimens of the tested materials for the ultimate tip cold bending test, and the test size is 60mm*60mm.

[0071] Step 2: The conventional ultimate tip cold bending test is used to determine the initial fixed loading stroke d 0 The specific method is: take an initial sample from the prepared bending specimen, placed on the test device in accordance with the technical requirements of the VDA238-100 technical standard for extreme tip cold bending test, until the pressure value reaches the closing threshold when th...

Embodiment 2

[0077] The present embodiment takes 1500MPa / 1.2mm of hot-formed steel bare plate as an example, using electron microscopy to assist observation to determine the crack state, the flowchart, such as Figure 6 The test flowchart for determining the equivalent fracture strain shown includes the following steps:

[0078] Step 1: Prepare bending specimens: According to the specimen size requirements specified in the VDA238-100 technical standard, prepare a number of bending specimens of the tested materials for the ultimate tip cold bending test, and the test size is 60mm*60mm.

[0079] Step 2: The conventional ultimate tip cold bending test is used to determine the initial fixed loading stroke d 0The specific method is: take an initial sample from the prepared bending specimen, placed on the test device in accordance with the technical requirements of the VDA238-100 technical standard for extreme tip cold bending test, until the pressure value reaches the closing threshold when the lo...

Embodiment 3

[0095] The present embodiment takes 1500MPa / 1.6mm aluminum-silicon coated hot-formed steel as an example, and gives the determination of the ultimate tip cold bend angle and equivalent fracture strain based on the simulation model, mainly to verify the effectiveness of the theoretical formula.

[0096] The simulation model is used to simulate the test conditions of VDA238-100, the mesh size of this model is 0.15mm, the equivalent fracture strain of the material determined by uniaxial tensile is 0.251, when the equivalent plastic strain reaches 0.251 is the material failure, in this simulation model, as long as one element reaches the equivalent fracture strain, it indicates that the test is terminated, and the specimen deformation state at this time is used to determine the ultimate sharp cold bend angle and the equivalent fracture strain.

[0097] The ultimate tip cold bend angle is directly determined for the simulation model termination state, and the measurement size is 48.2°,...