Analysis of the anti-fracture ability of common cold die material processing

Index used to evaluate failure resistance or bearing capacity: σs, σb, σf, Ak, etc. are usually used for the overall material. For cracked body (notch) JIC, KIC, and notch strength, etc. For ductile fracture materials, the experimental data measured by these indicators are relatively stable, with good reproducibility, and can better reflect the failure resistance indicators of the material.

For brittle fractured materials, including those with mixed fracture of toughness and brittleness, the evaluation of failure resistance is still incomplete. The main problem is that there is no obvious boundary between yield and fracture of this type of material; the material performance test data is highly dispersed and difficult to determine, so the evaluation of this type of material is different at home and abroad. To sum up, Huaxia Mould believes that:

(1) Brittleness is a material strength and plasticity index defined opposite to toughness. To evaluate the brittleness of materials, it is appropriate to use a comprehensive index of strength and plasticity. A single strength or plasticity index cannot fully describe the properties of brittle materials. (Guide: Requirements and technical analysis of surface finishing of molds)

(2) The brittle fracture process of materials is often the formation of crack propagation fractures from cracks without macroscopic cracks. Therefore, to evaluate the brittleness of materials, the brittleness of the material without macroscopic fracture and the brittleness of the material with cracks should be considered separately.

(3) Fracture evaluation of brittle materials without macroscopic cracks, using energy consumption evaluation at fracture, such as stress-strain area (or area under the force-displacement curve) such as tension, compression, bending, etc., and impact energy consumption energy. The surface roughness and defect size have a great influence on this performance measurement.

(4) Fracture toughness index evaluation for materials with cracked bodies: the energy consumed by propagating cracked bodies such as KICJICGIC, but the fracture toughness values u200bu200bof brittle materials are very low, and the uniformity of the tip shape and performance of the cracked body is used to measure the performance The impact is great, the fracture toughness distribution diagram of common materials is shown in Figure 6. After analyzing and calculating the actual load-bearing capacity of the W6Mo5Cr4V2 steel cold extrusion punch die, it is known that the brittle failure material can withstand working strain is thousands of times the fracture energy consumption, and almost all the energy is transformed into expansion kinetic energy, causing the punch to burst rapidly.

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