【摘要】：雙相鋼Q345多用于建筑或機(jī)械結(jié)構(gòu)的承力構(gòu)件,循環(huán)載荷的長(zhǎng)期作用使得構(gòu)件在低于其靜強(qiáng)度的載荷條件下發(fā)生疲勞斷裂,經(jīng)濟(jì)可靠的強(qiáng)度設(shè)計(jì)需要對(duì)材料的疲勞失效進(jìn)行研究。作者利用電磁諧振高頻疲勞試驗(yàn)機(jī),在載荷頻率140 Hz、應(yīng)力比為 1條件下,得到不同失效概率時(shí)材料高周疲勞(104周次疲勞壽命107周次)應(yīng)力 壽命(S-N)曲線。利用掃描電子顯微鏡觀察材料受到循環(huán)載荷作用后的顯微結(jié)構(gòu)的變化和疲勞失效后試樣的斷面微觀形貌,研究材料疲勞裂紋的萌生和擴(kuò)展。同時(shí),利用紅外熱像儀記錄Q345試樣表面的溫度場(chǎng)隨循環(huán)載荷作用周次的變化,研究材料在高頻循環(huán)載荷作用下的固有耗散能。雙相鋼Q345在高頻循環(huán)載荷作用下的疲勞失效主要是由于鐵素體 珠光體雙相結(jié)構(gòu)在循環(huán)載荷作用下的微觀強(qiáng)度差異使得微觀裂紋首先萌生于相對(duì)薄弱的鐵素體晶粒,且隨循環(huán)載荷周次的增加而裂紋逐漸擴(kuò)展。珠光體晶粒對(duì)疲勞裂紋的擴(kuò)展起阻礙作用,使得疲勞裂紋沿鐵素體或鐵素體與珠光體之間的晶界向前擴(kuò)展。當(dāng)載荷幅值低于其高周疲勞極限時(shí),試樣表面溫升不明顯;有限壽命的載荷條件下,試樣表面溫度場(chǎng)的變化受到材料微觀變形的影響,基于試樣表面溫度場(chǎng)的變化,能快速確定材料的高周疲勞強(qiáng)度極限。高頻循環(huán)載荷作用下,單位體積材料的固有耗散能與載荷之間呈非線性關(guān)系,在熱力學(xué)框架內(nèi)建立了材料的固有耗散能表征模型。
[Abstract]:Dual-phase steel Q345 is mostly used in load-bearing members of building or mechanical structures. The long-time cyclic load causes the fatigue fracture of the members under the loading condition below its static strength. The economic and reliable strength design needs to study the fatigue failure of materials. The high cycle fatigue (S-N) curves of materials with different failure probability were obtained by using electromagnetic resonance high frequency fatigue testing machine under the loading frequency of 140 Hz, stress ratio of 1. The microstructure changes of materials subjected to cyclic loading and the microstructure of specimens after fatigue failure were observed by scanning electron microscope (SEM) to study the initiation and propagation of fatigue cracks. At the same time, the temperature field on the surface of Q345 sample was recorded by infrared thermal imager with the cycle of cyclic load, and the inherent dissipation energy of the material under high frequency cyclic load was studied. The fatigue failure of dual phase steel Q345 under high frequency cyclic loading is mainly due to the difference in micro strength of ferrite pearlite dual phase structure under cyclic loading, which results in the initiation of microcracks at first in relatively weak ferrite grains. And the crack grows gradually with the increase of cyclic load cycle. The pearlite grain hinders the growth of fatigue crack, which makes the fatigue crack propagate along the grain boundary between ferrite or ferrite and pearlite. When the load amplitude is lower than its high cycle fatigue limit, the surface temperature rise is not obvious. The change of surface temperature field is affected by the micro-deformation of the material under the loading condition of finite life. Based on the change of the surface temperature field of the specimen, the high cycle fatigue strength limit of the material can be determined quickly. Under high frequency cyclic loading, the intrinsic dissipation energy of unit volume material is nonlinear to the load. A characterization model of inherent dissipation energy of the material is established within the framework of thermodynamics.
【作者單位】： 四川大學(xué)空天科學(xué)與工程學(xué)院;四川大學(xué)建筑與環(huán)境學(xué)院;
【基金】：國(guó)家自然科學(xué)基金資助項(xiàng)目(11327801;11372201) 長(zhǎng)江學(xué)者和創(chuàng)新團(tuán)隊(duì)發(fā)展計(jì)劃資助項(xiàng)目(IRT14R37)
【分類號(hào)】：TG142.1

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