| Summary: | 碩士 === 中國文化大學 === 材料科學與製造研究所 === 91 === Residual stress comes from many sources, all kinds of load、vibration、shock、temperature change of assemble may cause residual stress, among them the thermal stress at the welding zone may lead to residual stress, and eventually may cause damage to machine parts. In the past we have seen many great accidents caused by residual stresses or accumulation of them. For example, the plane crush of China Airlines happened in the end of May of 2002 was a typical one. The airplane flying under a normally condition at a high altitude was suddenly separated and divided into four parts. It was then proved to have been caused by the residual stress and the metal fatigue.
In this thesis there consist of two parts. The first part is the study of residual stress near a weld zone, including measurement of resistance with strain gage、photo-elastic method、X-ray diffractometer、finite element analysis etc. In this thesis, in the course of doing finite element analysis, we requested the equivalent terms of joint welded below value of residual stress, and also compared the use of computer model to simulate residual stress with real survey of resistance strain gage and value of residual stress, both of them are closely met. As a result, we have obtained the computed finite element value of 116Mpa, and the true stress of strain gage method as 112.25Mpa. These two methods have good match values. It also demonstrates that both two methods have a high reliability for residual stress measurement. In the finite element method, we have to include as a condition for input to match the test environment. In other words, we considered the change of Young’s modulus with respect to temperature.
Within this thesis, the second part is a Non-destructive Technique (NDT) using a Time Domain Reflectometry (TDR). In the past, most tests are based on some destructive techniques. This means that we had to examine an object by segment、cutting into slices、sampling to observe the condition and cause of the internal destruction, and to understand the damage mechanisms of the object. The Non-destructive Technique (NDT) we adapted was capable of “visualizing” the internal or mismatching by means of the TDR technique. A Non-destructive Technique (NDT) in terms of decision-making usually is far more rapidly available than a destructive technique.
Time Domain Reflectometry (TDR) is an electric machinery in time domain developed to measure the characteristic impedance、stray capacity、stray inductance etc. of a transmission line. In the field of testing materials the Time Domain Reflectometry (TDR) testing is relatively new in entry, yet it will soon join with other techniques in testing of weld quality and other material properties.
Keywords: residual stress, finite element analysis, strain gage, Non-destructive Technique, TDR, Time Domain Reflectometry, welding.
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