The therrno-mechanical balance equations for a porous material with big irregular pores are derived from the general ones for a medium with ellipsoidal microstructure by imposing the kinematical constraint of micro-st...The therrno-mechanical balance equations for a porous material with big irregular pores are derived from the general ones for a medium with ellipsoidal microstructure by imposing the kinematical constraint of micro-stretch bounded to the macro-deformation： in this case the microstructure disappears apparently （it becomes latent） and the response of the material involves higher gradients of the displacement without incurring known constitutive inconsistencies.展开更多
Micro-indentation tests at scales on the order of sub-micron have shown that the measured hardness increases strongly with the indent depth or indent size decreasing, which is frequently referred to as the size effect...Micro-indentation tests at scales on the order of sub-micron have shown that the measured hardness increases strongly with the indent depth or indent size decreasing, which is frequently referred to as the size effect. However, the trend is at odds with the size-independence implied by conventional elastic-plastic theory. In this paper, strain gradient plasticity theory is used to model the size effect for materials undergoing the micro-indenting. Meanwhile, the micro-indentation experiments for single crystal copper and single crystal aluminum are carried out. By the comparison of the theoretical predictions with experimental measurements, the micro-scale parameter of strain gradient plasticity theory is predicted, which is fallen into the region of 0.8—1.5 micron for the conventional metals such as copper (Cu), aluminum (Al) and silver (Ag). Moreover, the phenomena of the pile-up and sink-in near micro-indent boundary are investigated and analyzed in detail.展开更多
文摘The therrno-mechanical balance equations for a porous material with big irregular pores are derived from the general ones for a medium with ellipsoidal microstructure by imposing the kinematical constraint of micro-stretch bounded to the macro-deformation： in this case the microstructure disappears apparently （it becomes latent） and the response of the material involves higher gradients of the displacement without incurring known constitutive inconsistencies.
基金This work was supported by the National Natural Science Foundation of China (Grant Nos. 19891180 and19925211) jointly supported by the Fundamental Research Project from the Chinese Academy of Sciences (Grant No. KJ95-1-201).
文摘Micro-indentation tests at scales on the order of sub-micron have shown that the measured hardness increases strongly with the indent depth or indent size decreasing, which is frequently referred to as the size effect. However, the trend is at odds with the size-independence implied by conventional elastic-plastic theory. In this paper, strain gradient plasticity theory is used to model the size effect for materials undergoing the micro-indenting. Meanwhile, the micro-indentation experiments for single crystal copper and single crystal aluminum are carried out. By the comparison of the theoretical predictions with experimental measurements, the micro-scale parameter of strain gradient plasticity theory is predicted, which is fallen into the region of 0.8—1.5 micron for the conventional metals such as copper (Cu), aluminum (Al) and silver (Ag). Moreover, the phenomena of the pile-up and sink-in near micro-indent boundary are investigated and analyzed in detail.
