| PP material is widely used in the key engineering structure, which has many advantages. And now PP material has gradually replaced metal products, other plastics, natural and chemical fiber. Furthermore, PP material has very broad application in a number of industries, including agriculture, chemical industry, construction, engineering manufacturing, machinery and vehicle industry and it has become a major component of support for China’s economic development. Because of the research of fatigue damage mechanics properties for PP material is lack of information at present, particularly, the information of damage mechanism for PP is quite lack of, which is not helpful for the popularization and application of PP materials.So it is very meaningful to study the fatigue damage of PP material and promote the results to engineering application. The paper is based on the research of two different PP material (copolymerization polypropylene, Nano-CaCO3 modified polypropylene) which the purpose is to further explore the fatigue damage behavior and mechanism of PP material and expend application for other PP materials.The main research work and achievements of this paper are as follows:1) The basic mechanical properties of the two PP material were obtained by monoaxially stretching test, including the stress-strain curve, Young’s modulus and Poisson’s ratio of the material.2) According to the standard test method for fatigue crack growth rates of metallic material GB-T6398, C Y-K510 numerical control machine tool was used for specimen processing and material fatigue testing machine MTS810 was used for the study on two different PP material fatigue crack growth rates and mechanism. The number of cycles corresponding to each 0.5mm fatigue crack length growth was recorded during the text where the stress ratio R is 0.1, and then calculated the da/dN (The ratio of the fatigue crack length and number of cycles) andΔ K (Stress intensity factor) fatigue crack growth rates curve. Two different PP fatigue crack growths both can be divided into the initial stage, stable stage and rapid stage, and there was obvious toughening hysteresis phenomenon in the initial stage and obvious characteristics of the linear in the stable stage.3) The fatigue crack extension stable stage linear region was fitted and calculated the value of C and m value by Paris formula so that this part of the damage model was obtained. Finally, the toughening hysteresis verification test of the two kinds of PP material specimens with different initial crack length (Art tip length of 3mm and 5mm) were carried out.4) The real displacement field and strain field for PP test specimens(crack length is 1mm,2mm, 4mm,7mm) was calculated by using digital image correlation technique, high speed camera system and Vic 2D calculation software, also the Franc2D and ANSYS software were used to numerical simulate the crack tip stress field on the crack tip5) The microstructure of the fatigue crack section was photographed by scanning electron microscope (SEM). Different typical cross section areas were selected by scanning electron microscope so that very different cross section microstructures were gotten to dentally analyze and polyolefin materials and the mechanism of its toughening hysteresis phenomenon was studied and explored. It provides the reference for the fatigue damage properties of polypropylene.6) The AUTOCAD-ANSYS-LS-DYNA softwares had been used to finite element simulate and analyze the actual engineering application and a new concept of composite plate bumper had been presented, due to the discovery for the fatigue crack toughening hysteresis phenomenon of Nano-CaCO3-PP material. |
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