侵彻条件下两类靶体材料静阻力的探讨

Discussion on essences of static resistance of two types of material under penetration

以空腔膨胀理论为主要理论工具,通过比较侵彻近区塑性材料和脆性材料动力学行为的差异,对两类不同材料静阻力(Rt)的本质进行探讨,并对脆性材料侵彻的若干应用问题提出建议。研究表明:(1)Rt是靶体介质以固体特性抵抗局部扩孔、具有时间平均特性的弹体横截面平均应力,其具体取值随着材料的物理力学特性、侵彻模型、撞击速度等因素而变化,因此不是材料的固有特性。(2)对于塑性靶体的非变形侵彻问题,静态空腔膨胀理论的结果能够对Rt作出比较合理的预测;对于拟流体侵彻问题,一般需要对静态空腔膨胀理论的结果加以修正。(3)脆性材料的Rt主要取决于破碎后介质的力学特性而与完整材料的力学特性关系不大,且与单轴抗压强度之间不满足纯粹的单调关系;当侵彻速度较低时,应考虑侵彻速度对侵彻阻力的强化作用,这种强化作用的本质是内摩擦;当侵彻速度足够高时,脆性材料体现出恒定不变的"动力硬度",其反映了材料的本征阻力特性。(4)提高脆性材料的侵彻阻力的关键在于减小应力波峰值后环向拉应力的幅值、抑制材料的破碎速度和程度,具体措施包括主动或被动地增加外围压、对基质中添加增韧增强纤维等;为了实现对脆性材料侵彻问题更高精度的数值模拟,建议更加重视对破碎介质动力学特性的研究。

Based on cavity expansion theories,the very essences of static target resistance,i.e.Rt of plastic and brittle materials are discussed by comparing the difference of dynamic behaviors in near region of penetration,and some suggestions about applications of brittle materials for penetration are given.The summary of discussion is shown as follows.Firstly,Rt is the mean and time-averaged stress on the cross section of the projectile,which is the resistance of target materials in solid state against local cavity expanding.The specific value of Rt varies withphysical and mechanical properties of materials,penetration models,impact velocity and other factors,and thus is not an intrinsic property of material.Secondly,for the non-deformable projectile penetrating plastic materials,static cavity expansion theory is proper to predict Rt.For semi-hydrodynamic penetration cases,the results of static cavity expansion theory should be modified.Thirdly,Rt of brittle materials mainly depends on fractured materials,while it is weakly related to intact materials and not completely positively related to uniaxial compressive strength of intact materials.If penetration velocity is relatively low,the strengthening effect of Rt of brittle materials by penetration velocity increasing should be considered in terms of internal-friction.If penetration velocity is high enough,the intrinsic and constant resistance of brittle materials is realized,which is named as dynamic hardness.Fourthly,the key measures to increase Rt of brittle materials are to reduce the amplitude of hoop tensile stress following the peak compressive stress,to lower the crack velocity of materials and to restrain the fragmentation degree of materials.These can be solved by increasing external confining pressure and intensifying the tensile strength and fracture toughness of materials.Furthermore,it is suggested that the dynamic properties of fractured materials should be emphasized to increase the precision of numerical calculations of brittle materials under penetration.