AN EXPERIMENTAL-NUMERICAL METHOD FOR MEASURING CRACK PROPAGATING VELOCITIES UNDER STRESS WAVE LOADING

An experimental-numerical method for measuring dynamic crack propagating velocities under stress wave loading is established in this paper. The experiments of the three-point bend specimen are done on the improved Hopkinson bar. Deflection of loading point, dynamic load and instantaneous crack length are measured, then crack propagating velocities are calculated. Experiments on 40Cr steel show that the results given by this method have a good agreement with that obtained by the resistance fracture gage method. Therefore this method is feasible for measuring crack propagating velocities under high loading rate and will have wide application.     

基于信息元的教学资源组织系统设计与实现 *

以文本类型教学资源为研究对象,在领域知识可拓信息网模型和CELTS-3的基础上,阐述了基于信息元的教学资源组织系统设计与实现过程,包括信息特征元数据描述框架、特征词获取、信息元距离度量、信息元匹配规则以及匹配算法等.该系统通过有限的信息元描述无限的资源,实现了教学资源的高效组织,支持学习过程中资源自动重组.     

Carbon segregation and inclusions effects on surface fracture morphology of a 12% chromium stainless steel

Martensitic 12% chromium stainless steel is generally used for the manufacture of water vapour turbine blades. This material, under these environmental conditions, develops fatigue corrosion with failure as a result of the segregation of certain constituent elements such as phosphorus (P) and sulphur (S),^[1–3] or the presence of some types of inclusions.^[2–4] To be able to understand and explain these phenomena, in situ characterization of the fractured surfaces were performed for two types of samples: steel 1 as manufactured turbine material whose fracture mode is intergranular and steel 2 issued from last stage turbine blades after 100 000 h service at 40 °C whose fracture mode is transgranular. The techniques used for characterization were scanning electron microscopy (SEM) coupled with the x-ray analysis by energy dispersive spectroscopy (EDS), and auger electron spectroscopy (AES). The Auger results enabled the understanding of the brittle to ductile transition for the material by showing the simultaneous diffusion of carbon from grain boundaries (GB) to grains (G) and chromium from G to GB. Furthermore, the heavy segregation of phosphorus at the GBs could explain the intergranular crack rupture traces observed in steel 2. SEM observations coupled with EDS analysis showed the presence of different types of non-metallic inclusions such as silicon-based complex inclusions and manganese sulfides (MnS). The presence of silicon-based complex inclusions at GB could explain the intergranular fracture mode previously reported. The characterization of the fracture appearance suggests also that MnS inclusions can act as nucleation sites for secondary microcracks at the GB level that were observed after service.     

STUDY ON THE TENSILE FATIGUE DAMAGE OF QUASI—ISOTROPIC COMPOSITE LAMINATES

Quasi-isotropic. laminates have isotropic elastic properties in all in-plane directions. Therefore, this kind of laminate is widely used for structural elements. The simplest stacking sequence of quasi-isotropic laminates is [0/-60/60]s. When the direction of applied axial load to [0/-60/60]s laminate is inclined at a 30-degree angle, we have the other quasi-isotropic laminate [30/-30/90]s under axial load. The failure mechanisms of these two laminates are, however, entirely different from each other because these two laminates have different distribution of the interlaminar stresses. It was confirmed by tensile fatigue tests that the [0/-60/60]s laminate does not show any visible fatigue damage, but the [30/-30/90]s laminate develops edge-delamination during cyclic loading. The analytical results were in good agreement with the experimental results.     

THE INFLUENCE OF ENVIRONMENT ON FATIGUE AND FRACTURE OF IRON ALUMINIDES

ＴＨＥＩＮＦＬＵＥＮＣＥＯＦＥＮＶＩＲＯＮＭＥＮＴＯＮＦＡＴＩＧＵＥＡＮＤＦＲＡＣＴＵＲＥＯＦＩＲＯＮＡＬＵＭＩＮＩＤＥＳＳＴＯＬＯＦＦ，Ｎ．Ｓ．ａｎｄＡＬＶＥＮ，Ｄ．Ａ．（ＤｅｐａｒｔｍｅｎｔｏｆＭａｔｅｒｉａｌｓＥｎｇｉｎｅｅｒｉｎｇＲｅｎｓｓｅ...     

预应变对16MnR钢断裂韧性的影响SCIEI

本文实验发现预应变对16MnR钢的断裂韧性具有显著的影响,断裂过程中裂尖区域材料的组织结构发生了变化,裂纹在二次珠光体组织上扩展。16MnR钢断裂韧性的大小取决于碳原子的扩散及二次珠光体组织生成的难易程度。     

NiTi形状记忆合金螺钉的研制及医学应用

成功地研制了一种新型NiTi形状记忆合金螺钉并已临床应用了150例,经3年多考核,未发现骨不连及股骨头缺血坏死现象。     

TC11钛合金中氧铝偏析与脆性断裂

借助ＳＥＭ及ＥＤＡＸ、ＡＥＳ对某些ＴＣ１１钛合金棒材机械性能差的原因进行了研究。。结果表明材料延伸率、断面收缩率及冲击值低，显微硬度值高的拉伸和冲击断口上都呈现脆性解理断裂的断裂源，源区显微组织为条状α及空洞，且氧铝偏高。氧铝偏高造成α＋β→β相变温度和再结晶温度升高，使加工变形中形成的条状α在随后的热处理中得不到改变，并导致拉伸、冲击时的脆性断裂     

提高高铬白口铸铁磨球冲击抗力的技术关键

当高铬白口铸铁含铬量为18%～28%,Cr/C值是8￣9,铸铁的显微组织是回火马氏体 少量残余奥氏体(<5%) M7C3碳化物,则磨球具有高的冲击韧性和断裂韧性K1C,具有高的冲击抗力,表现出低的冲击剥落量。     

New high-temperature copper alloys

New high-strength, high-temperature Cu-Ni-Si alloys have been developed using additions of Cr, Zr, and/or Ti. These new alloys remain as precipitation hardenable as the base alloy, but the main strengthening phase may be different than Ni₂Si (e.g., Cr₂Ti). Substantial increases in mechanical strength were observed at both room and high temperature (773 K) when additions of Cr+Zr+Ti and Cr+Zr were made. Industrial testing of these alloys indicated a sevenfold increase in the lifetime of lateral blocks in continuous casting equipment of copper alloys.