材料期刊网

通过实验和有限元(FEM)计算研究了加载速率、缺口几何和加载方式对16MnR钢解理断裂行为的影响.结果表明,该钢的解理断裂机理及相应测得的细观解理断裂应力δf和宏观解理断裂应力δF不随加载速率、缺口几何和加载方式发生变化.不同缺口几何和加载方式试样的缺口韧性随加载速率的变化可以通过判据δyymax≥δF预测.δyymax为缺口前的最大正应力,可通过有限元计算得到.δF可作为一个工程缺口韧性参数用于含缺口类缺陷的结构完整性评定中.钢的δF值可用Griffiths-Owen 缺口试样在一个温度和加载速率下获得.

The changes in loading rate and test temperature influence deformation (yield and flow) and fracture behavior of steel.The most significant effect of increasing loading rate is to shift the quasi-static fracture toughness transition curve toward higher temperatures,that is,to raise the temperatures at which cleavage may occur.This is very critical for structural steel components.The high strain rate sensitivity of these steels makes the safety design on the basis of quasi-static behavior rather poor.Therefore.the reliability of structures possibly loaded at higher loading rates requires the knowledge of the corresponding material fracture behavior.However,the effects of loading rate on the cleavage fracture mechanism,fracture stress and toughness of various steels have not been understood completely.Specifically,the prediction of the cleavage fracture behavior in notched specimens and actual structures and components loaded at various loading rates remain to be learned.In engineering structures and components possibly loaded at various loading rates,notch defects malv be difficult to avoid and some notch-like geometries are necessary for structure design.Therefore,the understanding of notch toughness at various loading rates is also very important.In this work,the effects of loading rate.notch geometry and loading mode on the cleavage fracture behavior of 16MnR steel were studied by experiments and FEM calculations.The results show that the cleavage fracture mechanism of this steel,the corresponding local cleavage fracture stress δf and macroscopic cleavage fracture stress o-F do not change with the above three factors.The change of the notch toughness of the notched specimens with diirerent notch geometries and loading modes with loading rates carl be predicated by the criterion σyymax≥σF,where σyymax is the maximum normal stress ahead of a notch and can be obtainned by FEM calculations.The σF can be regarded as an engineering notch toughness parameter,and may be used for assessing the integrity of structures with notch defects.The erF values of steels can be measured by the Griffiths-Owen notched specimen at prescribed test temperature and loading rate.