摘要
研究金属材料在不同损伤机理时的基于电阻变化的损伤定义 ,在传导电流的导电截面与承载截面等价的假设条件下 ,其与有效截面的损伤定义等价。针对纯弯旋转高频疲劳试验 ,分析考虑材料损伤分布不均匀及电阻率变化的损伤最大值的测量公式 ,其具有超几何函数的形式 ;分析表明在材料损伤为 0～ 0 .6时其与假设损伤均匀且不计电阻率的情况差别不大 ,并提出一种近似公式。对结构钢的高周疲劳进行测量 。
The reliability of predicting fatigue lifetime depends on accurate measuring damage of materials. Usually, the damage is measured by choosing easy measuring parameters to be sensitive to damage evolution of materials. Damage measurement of metal materials based on electric resistance changes is a reliable method. In general, under the hypothsis of uniformly damage of specimen, previous research obtained the formula of measuring damage based on resistance changes. However, the resistance changes of the specimen depend on cross section, gauge length, temperature and resistivity change et al. Thus, the measuring damage formula based on resistance changes under considering variable gauge length, resistivity and uneven distributed damage of metallic specimen has to be investigated. In this way, the result of measured damage may reflect truly damaged situation of metallic materials. According to brittle and ductile damage mechanisms of metal materials, the definition of damage based on resistance changes was discussed. Under the hypothesis of a conducting section equivalent to a load bearing section, it is equivalent to the effective section definition of damage. On brittle damage, the gauge length change of specimen was neglectable, but may be considered on ductile damage. Usually, low cycle fatigue damage is ductile, and high cycle fatigue damage is brittle. On fatigue test of high frequency rotation bending by small smooth metallic specimens, the measuring damage formula was analyzed by considering uneven distributed damage and variable resistivity. Under the linear distribution of damage on distance to centroid of cross section of the rotation bending specimen and the formula of variable resistivity of satisfying Bridgman's law, the formula of maximum damage at the outmost specimen is a hypergeometric function. And the analysis result shows that the formula at damage of 0～0.6 is approximate to the situation of uniformly damage and negligible resistivity change. When the damage maximum in the cross section is larger than 0.6, the damage accumulation on the uneven damage model locates mainly in the zone of the outmost specimen, and increases quickly. So, at the same resistance change, the damage accumulation on the uneven damage model is quicker than the uniformly damage model. Specially, the measuring damage under considering uniformly damage and variable resistivity of metal materials is smallest. The corresponding approximate formula on the model of uneven damage and variable resistivity is obtained. And the formula of predicting fatigue lifetime on resistance change for metal materials is presented. At the different stress amplitudes, rotation bending high cycle fatigue damage of three structure steels, i.e. 45Carbon steel, 16Mn and 20Mn steel, was measured. The experimental results indicate that the measured damage of metal materials based on resistance changes agrees with the result by ductility dissipation method. The fatigue lifetime of metal materials was calculated by measuring electric resistance, and the results agree fairly with the theoretical prediction, respectively.
出处
《机械强度》
CAS
CSCD
北大核心
2002年第4期579-583,共5页
Journal of Mechanical Strength
关键词
金属材料
旋弯高周疲劳
疲劳寿命
电阻测量
Metal materials
Rotation bending high cycle fatigue
Fatigue life
Resistance measurement
