切口曲率半径对岩石断裂韧度K_(Ic)值的影响

本文对岩石三点弯曲试样的切口曲率半径与其断裂韧度 K_(Ic)值间的关系进行了详细的实验研究及理论分析.对岩石 K_(Ic)测试中切口的选择提出了建议方法.

切口圆棒试样测聚甲基丙烯酸甲脂断裂韧性可行性分析

根据聚甲基丙烯酸甲脂圆棒试样切口根部及裂尖钝化的应力应变特性 ,推导了聚甲基丙烯酸甲脂断裂韧性与临界切口半径 ρc的关系式。ρc 是材料常数 ,且当切口半径 ρ<ρc 时 ,尖切口问题转化为钝化的裂纹问题 ,此时应按断裂力学方法处理相关问题。实验结果表明 ,所测两种典型聚甲基丙烯酸甲脂的ρc>0 .2 5mm,因而 ,圆棒尖切口试样用于断裂韧性的估算具有现实的可行性。提出了一种简便的通过尖切口拉伸试验估算聚甲基丙烯酸甲脂断裂韧性的方法。

一九九八年全国高中数学联合竞赛加试试题及解答

一、(本题满分50分)如图,O、I分别为ABC的外心和内心,AD是BC边上的高,I在线段OD上.求证:△ABC的外接半径等于BC的旁切圆半径.注:△ABC的BC边上的旁切是与边AB、AC的延长线以及边BC相切的.证明 设AI的延长钱交圆ABC于K点,半径OK记为R.因为OK⊥BC,所以OK∥AD,从而AI/IK=AD/OK=c·sinB/R=2sinBsinC①AI/IK=S△ABI/S△KBI=[1/2AB·BI·SINB/2]/[1/2BK·BI·SIN(A+B)/2]=AB/BK·[sinB/2/(cosC/2)]

Elastic-plastic finite element simulation for diamond turning process

Using general commercial software, a coupled thermo-mechanical plane strain larger deformation orthogonal cutting model is developed on the basis of updated Lagrangian formulation in this paper. The workpiece is oxygen free high conductivity copper (OFHC copper), its flow stress is considered as a function of strain, strain rate and temperature to reflect its realistic changes in physical properties. In order to take into account the cutting edge radius effects of the single crystal diamond tool, rezoning technology is introduced into this simulation model. Diamond turning process is simulated from the initial stage to the steady stage of chip formation, and the distribution of temperature, equivalent stress, residual stress, strain rate and shear angle are obtained. The simulated principal force is compared with published experiment data and they are found to be in good agreement with each other, but poor for thrust force due to no consideration of elastic recovery for machined surface in the elastic-plastic material model.