| Fiber reinforced composite materials are widely used in aviation,aerospace,sea defense equipment and other important fields because of their excellent characteristics of light weight and high strength.Ultra-high molecular weight polyethylene（UHMPWE）fiber bundles are the most prevalent reinforcers in fiber-reinforced composites,and their properties are crucial to the performance of the composite materials.In order to completely comprehend the protective properties of UHMPWE fiber-reinforced composites and optimize the protective structure,it is particularly important to master the dynamic and static mechanical properties of UHMPWE fiber-reinforced composites.Firstly,at low speed（including quasi-static）,the influence of the strain rate effect on mechanical properties and failure modes of the ultra-high molecular weight polyethylene（UHMWPE）fiber bundles was investigated by axial tensile experiments.The contribution of elastic-viscoplastic properties and molecular bond fracture to fiber bundles’deformation was illustrated.In the strain rate range of 10-5s-1～3.3×10-2s-1,tensile experiments of UHMWPE fiber bundles were carried out in five different strain rate conditions,and the mechanical parameters and stress-strain curves were obtained.The statistical damage constitutive equation of fiber bundles,including the strain rate effect and the correction function,was fitted at normal temperature and low speed.The accuracy of the equation is good,and there are 4.04%,0.73%,6.45%,4.00%and 0.54%deviations between the tensile strength predicted by the equation and the measured value in the corresponding working conditions,respectively,which provides a reference basis for the accurate prediction of tensile strength of fiber bundles by monofilament parameters.Secondly,based on high-low temperature axial tensile experiments,more than 120 tests were carried out under 25 conditions including temperature（-60℃～80℃）and strain rate(10-5s-1～3.3×10-2s-1)to investigate the influences of temperature and strain rate effect on mechanical properties of UHMWPE fiber bundles.The results show that the mechanical properties of UHMWPE fiber bundles have certain strain rate and temperature effects,but the latter has a stronger influence,which makes the normal operating temperature of UHMWPE fiber bundles lower than 50℃.In addition,low temperature can improve the tensile strength of UHMWPE fiber bundles and weaken the strain rate effect of mechanical properties.In the range of-40℃to-60℃,the tensile strength and failure strain of UHMWPE fiber bundles are not affected by the strain rate.In the investigation of damage and destruction modes of UHMWPE fiber bundles,it is found that the critical strain rate of the brittle-tough transition is closely related to temperature in the temperature range（25℃～80℃）,and the critical strain rate will increase by an order of magnitude every time the temperature increases by about30℃.Finally,combining the theory of stress wave with the Abaqus finite element simulation,the value of the round trip number n of stress wave in the dynamic balance judgment theory is emphatically discussed.It is found that n≥3 is more reasonable for fiber bundle samples.Then,the finite element model of Split Hopkinson tensile bar（SHTB）that meet the requirements of axial impact tensile testing and dynamic balance theory,and the three phenomena in the waveform curve,such as the hysteresis of the step point of the transmitted wave,the shortening of the transmitted wave action time and the waveform oscillation,and the sag and abrupt at the peak platform of the reflected wave,were explained.The three phenomena can be essentially attributed to the superposition of elasto-plastic waves of different strength and phase.Subsequently,based on the two-wave method,the data processing of the waveform curve was carried out to obtain the stress-strain curve and dynamic constitutive equation of ultrahigh molecular weight polyethylene fiber bundle at high strain rate.Under the four strain rate conditions of 1060s-1,1450s-1,1925s-1 and 2328s-1,the maximum deviation between the results obtained from the constitutive equation and the simulation results is 9.52%,which has a high accuracy. |
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