| The rapid development of materials science and the growing awareness of environmental protection have brought new challenges to composites,and fully recyclable lightweight composites have become a hot spot in current research in various fields.Self-Reinforced polypropylene(SRPP)composites is made of polypropylene(PP)fiber or fabric reinforced PP resin.Its excellent impact resistance and interfacial bonding force can not only overcome the interfacial problems of heterogeneous composites,but also have a simple recycling process.It has specific economic and environmental benefits,and has received extensive attention in the fields of automobiles,sports equipment and safety products.However,the matrix and reinforcement of SRPP composites are thermoplastic materials,and their mechanical properties are very sensitive to temperature.In the process of designing and developing SRPP composites products,it is extremely difficult to predict their mechanical properties and mechanical responses.In addition,SRPP composites are prone to defects such as local breakage in the hot stamping process.There is no material library suitable for simulating SRPP composites in the preprocessing database of existing commercial simulation software.Therefore,in order to expand the commercial application of SRPP composites and provide constitutive relations for material simulation,it is necessary to conduct more in-depth research on the temperature effect of the mechanical properties of the material and the establishment of constitutive models.The purpose of this paper is to quantify the influence of temperature on the mechanical properties of SRPP composites,and to establish a simple and effective constitutive model that can accurately predict the mechanical behavior of SRPP composites at various temperatures.So as to provide a reference for the application,promotion and effective molding of this material.The specific research contents and conclusions are as follows:(1)The thermal properties of PP fibers,PP films and SRPP composites were tested and analyzed by differential scanning calorimetry.The results show: The glass transition of SRPP composites occurs at about-11.5 ?,and there are two melting peaks in the DSC curve,the melting point of the matrix in the composites is 150.2°C,which is 1.5°C higher than that of the PP film;the melting point of the reinforcement of the composites is 166.9°C,which is 4.1°C lower than that of the PP fiber.During the fusion process of PP fiber and PP film,the crystallinity of the PP resin matrix is improved,while the PP fiber is damaged to a certain extent.(2)The temperature effect of the mechanical properties of SRPP composites was explored,and the tensile properties,flexural properties and interlaminar shear properties of SRPP composites were tested and analyzed in the temperature range of-40?120 ?,as well as established empirical formulas between mechanical properties and temperature.The results show: As for the tensile properties,the tensile strength increases first and then decreases with the increase of temperature,and reaches the maximum value of 118.5 MPa at-20 ?.Below this temperature,interfacial debonding of the fiber and matrix is prone to occur,resulting in a decrease in strength.The elongation at break increases from 24.8% at-40 ? to 88.4% at 120 ?.The elastic modulus of the material in the glass state is always maintained at about 4.9 GPa,and it drops sharply when the temperature increases to-10 °C and then decreases gradually.For the flexural properties,both flexural strength and flexural modulus decrease with the increase of temperature.At-40 ?,the flexural strength and modulus reach the maximum,which are 113.7 MPa and 4.9 GPa,respectively,and decrease to 7.0 MPa and 0.2 GPa at 120 ?.The interlaminar shear strength decreases from 7.5MPa at 20 ? to 2.3 MPa at 120 ?,but is not significantly affected by temperature in the range of-40?0 ?.(3)The failure morphology of SRPP composites was observed by scanning electron microscope.The results show that as for tensile failure,the material exhibits brittle fracture when the temperature is lower than-10 ?.When the temperature is lower than-20 ?,the degree of debonding of the interface increases,which leads to the decrease of material strength.However,from-10 ? to 120 ?,the material exhibits ductile fracture.For shear failure,the shear failure mode is mainly interfacial debonding when the temperature is lower than-10 ?.When the temperature is higher than 20 ?,the shear failure mode is dominated by matrix failure.(4)Based on the tensile test data in the temperature range of 20?120 ?,a two-parameter phenomenological constitutive model of SRPP composites considering the effect of temperature was established,and the tensile stress-strain curve and strength modulus were predicted.The results show: The predicted curve is in good agreement with the experimental curve and the accuracy of the predicted tensile properties is high.That is,the phenomenological constitutive model proposed in this paper can accurately predict the tensile stress-strain curve and strength modulus of SRPP composites in the temperature range of 20?120 ?. |
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