车用木橡胶减震器动态力学性能及Johnson-Cook型本构方程

Dynamic Mechanical Properties and Johnson-Cook Type Constitutive Equation of Wood Rubber Shock Absorber for Vehicle

【目的】分析车用木橡胶减震器的力学性能求得车用木橡胶减震器Johnson-Cook型本构方程,并检验求得的本构方程对车用木橡胶减震器应力与应变关系的描述是否准确。【方法】选用密度0.439 g·cm^3、含水率约12%的小兴安岭红松木块及弹性好、黏接强度高、胶层柔韧、耐冲击、耐震动的氯丁胶作为试验原料,利用微米长木纤维成型机床沿纵向将干燥后的红松木块加工成微米级木纤维然后将加工好的木纤维放入揉丝机揉搓至宽度为1~2 mm、长度为15~30 mm的微米木丝再通过备料、称重、拌胶、模压、保压、卸模等工艺制备出车用木橡胶减震器试样。利用分离式霍普金森压杆对车用木橡胶减震器试样进行动态压缩试验,获得应变率为1 250,1 500,1 750 s^(-1)时木橡胶减震器的波形曲线。最后利用试验数据及Origin软件确定车用木橡胶减震器Johnson-Cook型本构方程的参数从而初步得到车用木橡胶减震器的Johnson-Cook本构方程,并对比试验曲线与Johnson-Cook型本构方程拟合曲线的拟合程度。【结果】模压出φ10mm×10mm的车用木橡胶减震器试样通过对试样进行动态压缩试验得到应变率为1 250,1500,1750 s^(-1)时车用木橡胶减震器的应力一应变曲线,利用试验所得数据建立车用木橡胶减震器的Johnson-Cook本构方程:σ=[21+0.329(ε)1.16]×[1+0.148ln(ε)]。[结论]车用木橡胶减震器对应变率比较敏感,能够实现较大的变形,并且在3种应变率下,流动应力的最大值均不小于12 MPa,远远超过目前较广泛应用于减震的氯丁橡胶和泡沫橡胶的最大许用应力,并且车用木橡胶的韧性及吸收能量的性能要比氯丁橡胶及泡沫橡胶好。通过对试验后试样的损伤进行观察,发现当应变率为1 500 s^(-1)时车用木橡胶减震器试样上出现450的表面裂纹并且车用木橡胶减震器的破坏形式均以胶的破坏为主。在观察试验曲线与Johnson-Cook型本构方程拟合曲线的拟合程度后,可以发现在应变较小时,求得的Johnson-Cook型本构方程对车用木橡胶减震器应力与应变关系的描述比较准确,尤其在应变率为1 250 s^(-1)且应变小于0.056时,拟合值与试验值几乎完全吻合。

[ Objective] The main purposes of this paper is to analyze the mechanical properties of wood rubber shock absorber for vehicle, to obtain the Johnson-Cook constitutive equation and to check out whether the equation can exactly describe the relationships of stress and strain for wood rubber shock absorber for vehicle. [ Method] We select the small Xing＇ an mountain Korean pine （Pinus koraiensis） wood with the density of 0. 439 g .cm^-3 and moisture content of 12% , ehloroprene rubber which has good elasticity, high bonding strength, flexible layer, resistant to impact and vibration is also used as experimental materials. Micrometer-level fiber forging machine is applied to process the dried red pine wood into wood fiber, then put these wood fiber into the kneading machine, and obtain the micro wood fiber with width of 1 - 2 mm, length of 15 - 30 mm. The specimens of wood rubber shock absorber for vehicle were prepared by several processes including the preparation, weighing, mixing, molding, holding pressure, unloading, and so on. Dynamic compression tests on the specimens of wood rubber shock absorber for vehicle are performed by using Split Hopkinson pressure bar, andget the curves at the strain rate of I 250 s^-1 , I 500 s^-1 and 1 750 s^-1, respectively. Finally, using the experimental data and Origin software to ascertain the parameters of Johnson-Cook constitutive equation, then the Johnson-Cook constitutive equation, and the experimental curve and the curve fitted by the Johnson-Cook constitutive equation is established and compared, respectively. [ Result]Theφ 10 mm × 10 mm specimens of wood rubber shock absorber for vehicle were made, the stress and strain curves at the strain rate of 1 250 s-~ , 1 500 s-~ and 1 750 s ~ were obtained by dynamic compression tests, and the Johnson-Cook constitutive equation （ o- = [21 ＋ O. 329（ε）1.16] × [ 1 ＋ 0. 1481n（ε＊） ] ） of wood rubber shock absorber for vehicle are successfully established. [ Conclusion] By analyzing the stress and strain curves of wood rubber shock absorber for vehicle, we can see that the wood rubber shock absorber is sensitive to the strain rate, it can realize a large deformation, the maximums flow stress are higher than 12 MPa under the three strain rates in this study, this is far more than the maximum allowable stress of cellular rubber and neoprene which are widely used as shock absorbing in the present. Furthermore, the toughness and energy absorption properties of wood rubber are also better than chloroprene rubber and cellular rubber. After dynamic compression tests, the specimen of wood rubber shock absorber for vehicle showed 45° splitting damage on surface when the strain rate is 1 500 s^-1, and the destruction is mainly occurred on gum. The fitting degree of the experimental curve and the curve fitted by the Johnson-Cook constitutive equation is good when the strain is smaller, especially at the strain rate of 1 250 s^-1 and a strain of less than O. 056, the fitted value is almost completely coincide with the experimental value.