中文摘要：

应用复型技术和逆序观测法对LZ50车轴钢光滑试样的早期疲劳短裂纹扩展行为进行试验研究。根据有效短裂纹理论,采用当量I型主导有效短裂纹的概念描述材料群体疲劳短裂纹萌生、扩展的规律,利用最大微观结构障碍的概念推导该材料的疲劳起裂阈值及疲劳强度。研究结果如下：每个试样的有效短裂纹起源于试样表面的某些铁素体,这些裂纹萌生和扩展过程具有强烈的随机多裂纹特征;由于受最大微观组织障碍的约束,当量I型主导有效短裂纹的扩展率具有初期下降和后期上升的特征;疲劳短裂纹的起裂阈值与最低扩展率和最大材料微观组织障碍相关,其值为1.973 76MPa.m0.5;起裂阈值所对应的疲劳强度具有随表面缺陷当量尺寸的增加而下降的特点,当尺度大于50μm时,疲劳强度低于常规疲劳极限。

英文摘要：

Early propagation behavior of short fatigue cracks on small smooth specimens of railway LZ50 axle steel was experimentally studied with the replicating technique and reverse observation technique. The initia- tion and propagation of collective short fatigue cracks were described in terms of the concept of equivalent type I dominant crack in effective short fatigue cracks according to the effective short fatigue theory. And the fatigue cracking threshold and corresponding strength of the material were deduced in consistency with the maximum micro-structural barrier capacity of the material. The research results reveal as follows： The effective short fa- tigue cracks of all specimens originate from the weakest surface ferrites, and their processes of initiation and propagation are strongly subjected to a random multi-cracks system; because of the maximum micro-structural barrier effect, growth rates of the equivalent cracks are characterized by early-stage descending and later-stage ascending; the deduced fatigue cracking threshold corresponding to the maximum micro-structural barrier is 1. 973 76 MPa·m0.5 ; the fatigue strength corresponding to this threshold tends to decrease with increase of the equivalent crack size, and this strength will be lower than the conventional fatigue limit when the material has a surface defect with an equivalent crack size over 50μm.