【摘要】 本文以实验为基础,研究了在弹塑性状态下,LY12CZ薄板铝材裂纹起裂,稳态扩展和失稳扩展时的行态。采用特制的涡流裂纹自动跟踪仪,较精确地得到裂纹扩展量△a_p的连续记录。在此基础上,测得真实裂纹端的张开位移COS和张开角CTOA,从而得到用它们表征的、完整的裂纹扩展阻力曲线,即COS-△a_p和CTOA-△a_p曲线。实验表明:LY12CZ薄板铝材裂纹起裂时的张开位移δ_c是一稳定的常值,在起裂后的稳态扩展阶段,张开角CTOA是一稳定的常值。本文结合理论分析后指出,对一般韧性材料,在dδ_p/da》σ_s/E时,其张开角确应是材料的抗裂特性。在实验中还发现,在裂纹扩展一定值后,实测的张开角突然下降,此现象对应于裂纹的失稳扩展。更多还原

【Abstract】 The fracture behaviour of metallic sheets made of aluminum alloy LY12CZ has beeninvestigated experimentally with regard to crack, initiation, stable crack growth and unstablecrack propagation under elastic-plastic conditions. By means of an eddy-current device,specially designed for the automatic tracking of the advancing crack tip, it was possible torecord the crack growth △a_p accurately and continuously. The crack-opening displacementat current crack tip COS and the crack-tip-opening angles CTOA have been obtained. The-refore, complete R-curves characterizing the resistance to crack propagation in terms ofCOS and CTOA, i.e., curves of COS vs. △a_p and CTOA vs. △a_p have been obtained aswell. It has been shown from the experimental results for the LY12CZ sheets that thecrack-opening displacement at crack initiation, δc, tends to a constant value; the crack-op-ening angle at the current crack tip also tends to a constant value during the process ofstable crack growth after its initiation. It has further been argued from some theoretical considerations that for any ductile material having the property dδp/da》σ₅/E, the dimen-sionless parameter dδp/da could indeed be taken as a material characteristic representing itsresistance to stable crack growth. However, after a certain amount of stable crack growth,the experimentally measured value of CTOA was found in the present investigation to dec-rease abruptly at a stage corresponding to the occurrence of unstable crack propagation.更多还原