摘要
在恒应变控制下测试调质合金钢试样 90 %存活率的疲劳寿命Nf,然后将其他试样分别疲劳损伤到 0 .1Nf、0 .2 5Nf、0 .5Nf、0 .8Nf周次后进行中间退火 ,再继续测试剩余疲劳寿命。结果表明中间退火可以延长疲劳寿命。微观检验表明 :调质钢是由弥散碳化物质点和铁素体组成的两相组织 ,碳化物是裂纹源。借助于静载荷下解理断裂的微观力学模型和公式 ,可以解释微观参数对在碳化物或碳化物与基体界面萌生微观裂纹和向基体延伸的影响 ,但必须考虑随着疲劳损伤而发生的微观参数的变化。用此微观力学模型和公式也可以解释中间退火延寿机理。中间退火消除了胞状结构 ,使杆状碳化物转变成球状碳化物 ,减少了应力集中、扩散了晶区的有害元素 ,恢复和提高了萌生裂纹的表面能 ,恢复了材料的有效门槛值ΔKth·eff,减慢了由微观裂纹向宏观短裂纹扩展速率 。
The fatigue life N f of Quenched and high temperature tempered alloying steels specimens were measured at constant strain amplitude with 90% survival probability. Then other specimens were fatigue damaged to 0.1 N f,0.25 N f,0.5 N f,0.8 N f cycles, respectively. The damaged specimens were healed by intermediate annealing, then the retained fatigue life were measured. The experiments showed that the intermediate annealing can prolong the fatigue life. The micrography indicated that the tempered alloying steels are composed of two phases, ferrite and precipitated carbide particles that are the site of initiating cracks. By means of the micro fracture mechanics models and formulas of the static cleavage, it could be explained that the influence of the micro parameter on both crack initiation at carbides or carbide matrix interface and extending into matrix. However, the micro parameter variation during fatigue damage process should be taken into consideration.The micro mechanics of prolonging remains life can be explained by the micro fracture mechanics models and formulas. The intermediate annealing eliminates cell structure of dislocation, turns rod type carbides to spherical ones, reduces stress concentration, diffuses harmful elements, resumes or increases the surface energy needed to initiate cracks, recovers the effective crack growth threshold, Δ K th·eff , slow down the crack growth rate from micro crack to macro short crack, so the fatigue life get recovering or increasing.
出处
《机械强度》
CAS
CSCD
北大核心
2002年第4期613-616,499,共5页
Journal of Mechanical Strength
基金
国家自然科学基金资助项目 (金属材料疲劳及性能恢复的仿生研究
59931 0 2 0 )
