臺灣博碩士論文加值系統

本文提出一種延遲疲勞裂縫成長的修補方式, 係在對塑性板材的裂縫
尖端局部處加入熱量, 而此局部高溫所形成的溫度場會因材料性質的改
變, 造成裂縫尖端集中應力場的緩和,並且能在外力卸載之後於裂縫尖端
局部處產生一特定的塑性區域. 根據Wheeler Model,此特定塑性區域產生
的殘留壓縮應力可以有效的延遲疲勞裂縫進展, 本文以含有裂縫的鋁合金
A5083P-O板材加以驗證. 透過建立疲勞實驗系統, 溫度量測實驗系統
及CCD影像擷取系統, 記錄各實驗試片a-N的曲線, 並比較局部熱應力對殘
留應力的影響, 再將加熱過程的裂縫尖端表面的變化以影像的方式擷取下
來, 作定性的外觀描述. 本文也透過掃瞄式電子顯微鏡作斷口金相觀察,
藉此推測加熱當時的受力狀況, 並找出局部加熱法的斷口金相特徵.
為了重現實驗過程, 本文利用ANSYS有限元素套裝軟體及其所附的APDL專
屬程式語言,在給定材料性質及邊界條件之後, 來加以模擬定幅負載下於
加熱過程中單一週次疲勞作動期間試片之應力應變分布, 並利破壞力學中
的CTOD值及 J積分值來作為加熱效果的定量描述, 再與過大負荷所造成的
效果作比較. 實驗結果符合吾人當初的假設, 證明本方法對疲勞裂縫
的進展確實有效, 且其應力分布的情形與過大負荷法造成的應力分布相
似, 在實用性方面是深具潛力的.

This study provides a whole new crack reparing method by
depressing fatiguecrack growth rate. We input local heat energy
near the crack tip of plastic thin plate and divergent
temperature contour resulted. The specfic temperature field may
loosen the original stress concentrated field near the reign of
crack tip by the changing material mechanical properties and
produce a certainly kind of plastic zone near the reign of crack
tip by released applied force. According toWheeler''s retardation
model, the residual compression stress generated by this
certainly kind of plastic zone would depress fatigue crack
growth rate effectively. So we prove this assumption by the
material aluminum A5083P-O within edge crack successfully. By
established fatigue crack growth system, temperature measure
system werecord the a-N curve of each experimental speciman and
compare the efficiency with different residual compression
stress resulted by different local inputheat. By established CCD
camera picture capture system, we describe the variousoutline of
each experimental 中specimen sequentially. Furthermore, we use
SEM to analysis the kerfs by micro fractography. Modeling the
actual condition which is half cyclic loading and within
heatinput by using APDL language of ANSYS to write a program, we
know something interesing in the whole process. By calculating
von-mises stress, CTOD and Jintegral with variable time in the
fracture mechanical theory, we know the similarities and
differences between overload method and local heat input method.
Finally, we know the local heat input method can depress fatigue
qrowth more efficiently, and the compression stress distribution
is similarity with overload method. We know deeply that it is
potential in practice.