本文主要是利用霍普金森高速扭轉試驗機(Torsional Split-Hopkinson Bar)來探討及比較304L不銹鋼定電流與脈衝電流電漿銲接件之動態機械性質及破壞特性。實驗條件在室溫(25℃)下，應變速率分別為900 s-1、1300 s-1、1900 s-1、2200 s-1、2600 s-1與3300s-1的範圍內，分析並比較定電流與脈衝電流銲接件在高速扭轉荷載下所產生的塑變行為與破壞形貌的差異，同時藉助一構成方程式用以描述本材料在動態扭轉荷載下的破壞行為。
經由本實驗所得數據分析結果，可得知應變速率對304L銲接件產生相當明顯的影響。隨著應變速率的上升，兩組銲接件的塑流應力、加工硬化率、應變速率敏感性與材料內部升溫量均隨之上升，熱活化體積則隨之下降。而在同一應變速率區間內，隨應變量的提升，銲接件的應變速率敏感性也隨之升高，相反熱活化體積則隨之下降。在相同應變速率下，脈衝電流銲接件的塑流應力、加工硬化率、升溫量與應變速率敏感性均較定電流銲接件來得大，唯熱活化體積方面則較小。在破壞觀察方面，經由光學顯微鏡發現剪切面會經過銲道(FZ)、部分熔融區(PMZ)與熱影響區(HAZ)，且裂紋兩側流線有明顯的扭曲現象，明顯是屬於剪切帶破壞。另外在掃瞄式電子顯微鏡觀察顯示出，304L銲接件的剪切面主要由銲道、熱影響區韌窩與平滑淺韌窩所構成。隨著應變速率的增加，兩組銲接件的銲道與熱影響區韌窩密度皆有隨之增加的趨勢，而平滑淺韌窩所分佈的區域則減少。在同一應變速率下，脈衝電流銲接件破斷面上的韌窩較小且較密集，這也代表脈衝電流銲接件具有比定電流銲接件較高的破壞應變量。最後結合巨觀機械性質與微觀結構的特性，以Kobayashi & Dodd模式之構成方程式來描述304L不銹鋼電漿銲接件在高速扭轉下的塑變反應，以作為工程結構設計之應用及參考。

The dynamic shear plastic deformation behavior and fracture characteristics of continuous current (CC) and pulsed current (PC) plasma arc weldments of 304L stainless steel under six strain rates (900s-1, 1300s-1, 1900s-1, 2200s-1, 2600 s-1 and 3300s-1) are studied at room temperature (25℃) by means of torsional split-Hopkinson bar. Results indicate strain rate significantly influences 304L weldment mechanical properties. Increasing strain rate increases flow stress, work-hardening rate, strain rate sensitivity and temperature rise of 304L weldments. For all tested strain rate ranges, strain rate sensitivity increases as strain increases, but activation volume decreases. The shear stress, work-hardening rate, temperature rise and strain rate sensitivity of PC weldments are all higher than those of CC weldments in the same strain rate, but only activation volume is lower. OM shows cracking is through the fusion zone, partially melted zone and heat affected zone. Flowlines are clearly twisted at both sides of the crack. Fracture is due to shear band formation. SEM shows fracture surfaces consist of fusion zone dimples, heat affected zone dimples and smooth shallow dimples. Increasing strain rate increases density and depth of FZ and HAZ dimples, but smooth shallow dimples decrease. This tendency is more significant in PC weldments than in CC weldments. The Kobayashi & Dodd constitutive equation successfully describes the high-strain-rate shear plastic behavior of 304L weldments.

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