Establishment of X-Ray Fractography as Failure Analysis Method

1. 断裂面x射线衍射观察为分析工程结构破坏事故的原因提供了有用的信息。这种实验技术被称为x射线断口学。以下四个x射线参数已被证实可用于确定断裂的模式和力学条件：残余应力，半最大全宽度（FWHM），衍射图和相变相。利用衍射图的计算机图像处理，确定了低碳钢疲劳断口最大屈服区内的反向屈服区。FWHM的分布对这两种带的确定也很有用。虽然在断口表面测得的残余应力大多为拉应力，但在高平均压应力下的疲劳断口和混合模式加载下的剪切断口上测得的残余应力为压应力。建立的室温空气疲劳断口x射线断口分析方法适用于腐蚀疲劳和高温疲劳。蠕变断口的定量分析有待进一步研究。测量的氧化铝断口下残余应力分布可用于确定塑性区的深度。用x射线法测得的断裂面下塑性区深度由应力强度因子与材料屈服强度的断裂力学方程表示。x射线断口技术已成功应用于轴、销、轴承和高温材料的断裂事故中。

1. X-ray diffraction observation of fracture surfaces yields useful information to analyze the causes of failure accidents of engineering structures. This experimental technique has been maned X-ray fractography. The following four X-ray parameters have been confirmed useful for determing the mode and mechanical conditions of fracture: residual stress, full width at half maximum (FWHM), diffraction pattern, and transformed phase.2. Computer image processing of diffraction patterns was use to determined the reversed yeild zone within the maximum yield zone on the fatigue fracture surface of mild steel. The distribution of FWHM is also useful for this determination of two kinds of zone.3. Although the residual stresses measured on fracture surfaces were tension in most cases, the compressive residual stresses were detected on the fatigue fracture under a high compressive mean stress and on the shear fracture surface made under mixed mode loading.4. The X-ray fractographic methods established for fatigue fracture in air at room temperature were found to be applicable to corrosion fatigue and high temperature fatigue. Quantitative analysis of creep fracture surface is left for a future study.5. The measured distribution of residual stresses beneath the fracture surface of alumina was usable for determining the depth of the plastic zone.6. The depth of the plastic zone beneath fracture surfaces measurd by X-ray methods is expressed by a fracture mechanics equation of the stress intensity factor and the material yield strength.7. X-ray fractographic techniques were successfully applied to fracture accidents in service of shaft, pin, bearing and high temperature materials.