本研究針對硬銲型板式熱交換器進行加壓－洩載循環的疲勞實驗及壽命評估並測量接頭中心處底層蓋板的變位及尋找疲勞破裂位置。定義疲勞壽命之循環數，利用ANSYS Code配合多軸疲勞準則，進行二維及三維有限元素疲勞壽命分析，低週期疲勞壽命準則採用ASME Code N-47的最大等效應變範圍準則，高週期疲勞壽命準則採用Fuchs的最大剪應力範圍準則。

　　分析結果顯示疲勞初始裂紋產生於兩山形紋板片間的銅銲點處及其裂紋成長方向皆與實驗結果吻合。剪應變振幅對低週期疲勞壽命準則貢獻最大，同時壽命預估值比實驗值保守，差異多數在一倍分散因子內，具實際應用之參考價值。剪應力振幅對高週期疲勞壽命貢獻最大，目前實驗進行至 105 循環尚未達壽命估算值，故無法比對。

　　爲提高低週期疲勞壽命，本文在底層蓋板刪除低應力區之材料，以降低銅銲點的剪應變振幅，分析結果銅銲點應力應變大小皆有改變，破裂點及裂紋成長方向與改良之前比較不受影響，但疲勞壽命提高。

　In this paper, constant pressure amplitude cyclic fatigue experiments and life estimation the Braze Plate Heat Exchanger were studied, with a measurement of under-plate the displacement beneath the center of part and a searching method of finding the position of fatigue crack.By define the number of cycles to fatigue failure and employ the ANSYS Code with multiaxial fatigue criteria 2D and 3D Finite Element life analysis were performed. For the low cycle fatigue (LCF) life the ASME Code Case N-47 was used, however, for high cycle fatigue (HCF) life the Fuchs’ maximum shear stress range criterion was employed.

　Both the analytic results showed that the crack initiations locater at the braze copper between the two inner plates. The shear strain amplitude had the greatest effect on LCF life and the predicted life was conservative and had a longer life than the experimental life with scattering factor of one. Also the shear stress amplitude had the greatest effect on HCF life. Comparison of predicted HCF life with experimental data was not completed, since the experiment is still running beyond 105 cycles.

　This paper also showed that through an elimination the material under low compress stress within the under-plate could reduce the shear strain amplitude of the braze copper and hence increase the life without changing the location of crack initiation and its growth direction.®

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