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Hydrogen Embrittlement and Low Cycle Fatigue Fracture of High Strength Steel Screw
|Contributors: ||NTOU:Institute of Materials Engineering|
|Issue Date: ||2011-06-28T07:09:32Z
In this work, AISI 1022 steel wire was used for making high strength concrete screws, which were carburized and tempered at distinct temperatures after shaping. Besides, some of the screws were subjected to baking at 200oC/3hr after electro-plating. Constant loading in salt water at 80oC was performed to evaluate the hydrogen embrittlement susceptibility of the screw. Moreover, bending fatigue tests were carried out to determine the fatigue strength of the screw under the criterion of resisting 105 cyclic loading. The results indicated that those screws tempered at lower temperature possessed higher strength and greater torque but lower bending angle than those tempered at higher temperatures. Modification of screw teeth geometry to lower the stress concentration in the threaded portion was found to effectively increase the screw torque and bending angle of the concrete screw. Under constant loading in tension, those modified screws showed similar resistance to hydrogen embrittlement in salt water, despite of tempering at 300 or 320 oC. Sustained bending tests under constant torque showed baking treatments had beneficial effects to reduce the susceptibility to hydrogen embrittlement. However, increasing the radius below the screw head or decreasing stress concentration effect was found to effectively reduce the likelihood of cracking/fracture of screw during sustained bending tests under constant torque. The results of bending fatigue tests showed the discontinuity below the screw head played the most important role in affecting the fatigue strength of concrete screws.
|Appears in Collections:||[材料工程研究所] 研究計畫|
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