Deformatio and Fracture of Materials at High Strain Rates and Cryogenic Temperature

高应变率和低温下材料的变形和断裂

基本信息

批准号：
61550058
负责人：
KISHIDA Keizo
金额：
$ 1.41万
依托单位：
Osaka University
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (C)
财政年份：
1986
资助国家：
日本
起止时间：
1986 至 1987
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/grant/KAKENHI-PROJECT-61550058/
关键词：
Cryogenic Temperature High Strain Rate Flow Stress Yield Stress Dislocation Thermal Activation Theoty Fracture Toughness 負荷速度塑性変形双晶

项目摘要

The objective of this research is to provide the basic understanding on deformation and fracture of materials at high strain rates and cryogenic temperature. Strain rate and temperature are the most important parameters which affect the mechanical behavior of metals. The influences of strain rate and temperature on the flow stress have been investigated from macroscopic and microscopic standpoints. Successful explanation of these influences on the yield stress has been given by the thermal activation theory of dislocation. On the other hand, the effects of temperature and loading rate on fracture toughness have not been made clear experimentally or theoretically. In this research experimental techniques have been developed for investigating mechanical behavior of materials at high strain rates and cryogenic temperature using dynamic testing systems and liquid helium cryostats. Yield stress and fracture toughness for low-carbon steels were measured at the trmperature range of 4 K to 298 … More K and various strain rates from quasi-static to impact loading conditions. The fracture toughness was dropped with decreasing temperature and increasing loading rate. The brittle-to-ductile transition was shifted to higher temperature range by the increase of the loading rate. The fracture toughness decreases with increasing the yield stress. This fact denotes that the plastic deformation around a crack tip is tightly related to the fracture toughness. Several studies were presented in view of the dislocation motion around the crack tip; the emisson of dislocations from the crack tip, the stress field around the crack tip shielded by a dislocation pile-up and so on. In this research a computer simulation of the brittle-to-ductile trnsition has been carried out using a simple model where the emission of dislocations from the crack tip is thought to arise from a thermally activated process. The computaional result seems to roughly reproduce the brittle-to-ductile transition observed experimentally. According to the present model, the increasing loading rate is equivalent to the lowering temperature. The experimental data available have been discussed in the light of the present model. Less

这项研究的目的是在高应变速率和低温温度下对材料的变形和裂缝提供基本理解。应变率和温度是影响金属机械行为的最重要参数。应变速率和温度对流动应力的影响已从宏观和微观的角度研究。这些影响的成功解释是由热激活理论给出的。另一方面，温度和加载速率对断裂韧性的影响尚未在实验或理论上明确。在这项研究中，已经开发了用于使用动态测试系统和液态氦低温器以高应变速率和低温温度以高应变速率和低温温度进行机械行为的开发。在4 K至298的Trmperature范围内测量低碳钢的屈服应力和断裂韧性……从准静态到影响负载条件的各种应变速率以及各种应变速率。裂缝韧性随温度降低并增加负荷速率下降。通过增加负载速率，脆性到延性的过渡转移到了更高的温度范围。断裂韧性随着增加的屈服应力而降低。这一事实表明，裂纹尖端周围的塑性变形与断裂韧性密切相关。鉴于裂纹尖端周围的脱位运动，提出了几项研究。裂纹尖端的脱位紧急，裂纹尖端周围的应力场被脱位堆积等屏蔽等等。在这项研究中，使用一个简单的模型进行了对脆性trnsition的计算机模拟，其中认为裂纹尖端的位错的发射被认为是由热激活的过程引起的。计算机结果似乎大致繁殖了实验观察到的脆性转变。根据目前的模型，增加的加载速率等于降低温度。根据本模型，已经讨论了可用的实验数据。较少的