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目前,砖混结构,出现温度裂缝已属普遍现象,其程度轻重不一,轻微的,不影响正常使用,而严重的则影响安全使用,更为突出的是造成用户心理上不安全感并影响墙面美观。由于气温变化,尤其在北方地区四季昼夜温差大,往往在顶层墙体、屋面和挑檐等部位,不同程度的出现温度裂缝,既破坏了结构 相似文献
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通过多年的现场观察,结合查阅有关混凝土内部应力方面的专著,对混凝土温度裂缝产生的原因、现场混凝土温度的控制和预防裂缝的措施等进行深入的阐述。指出引起裂缝的原因主要是温度和湿度变化等。并提出采取防止裂缝的相应措施。主要改善内部和外部约束条件。 相似文献
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大体积混凝土施工的一个特点是容易产生温度裂缝,在安钢新1^#高炉混凝土基础施工中,采取控制混凝土技术条件,加强测温监控等措施,实行“温差-温度应力”双控制,避免了温度裂缝产生,取得了较好的效果。 相似文献
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本文对某工程地下室纵墙裂缝发生的成因,机理过程进行分析,表述了对带有地下室框架结构温度变开缝的认识,提出地下室纵墙裂缝的防治措施。 相似文献
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论述了砌体结构房屋内裂缝出现的原因、形式,以及预防方法和治理的措施等,提出了控制裂缝应以预防为主治理为辅的原则。 相似文献
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XUTao LIFeng CHENHua YUCui-yan 《钢铁研究学报(英文版)》2005,12(4):40-43,49
The formation and growth of thermal fatigue crack in low chromium semi steel were investigated by means of optical microscope and scanning electron microscope, and the function of RE in low-chromium semi steel was analyzed. The results show that the thermal fatigue cracks are mainly generated at eutectic carbides, and the cracks not only grow and spread but also join each other. RE can improve the eutectic carbide‘s morphology, inhibit the generation and propagation of thermal fatigue cracks, and therefore promote the activation energy for the crack‘s propagation, which is especially more noticeable in case of the RE modification in combination with heat treatment. The mathematical model of the crack propagation is put forward. 相似文献
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利用实验室条件下冶炼的Fe-Cr-Nb-Mo铁素体不锈钢,对其高温强度和热疲劳性能进行了研究。研究结果表明:实验钢的高温抗拉强度和屈服强度优于或基本相当于目前所使用的铁素体不锈钢的性能;实验钢的热疲劳裂纹从V形缺口处萌生,夹杂物为裂纹萌生优先区域;热疲劳裂纹长度和扩展速度随热疲劳上限温度的升高而增大;热疲劳裂纹优先沿晶界扩展,高温氧化是疲劳裂纹扩展的主要因素。 相似文献
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显微组织结构对GJW35钢结硬质合金热疲劳性能的影响 总被引:2,自引:0,他引:2
尤显卿 《稀有金属与硬质合金》1999,(2):22-27
分析了热处理后GJW35钢结硬质合金的显微组织结构,研究了显微组织对合金的热疲劳裂纹萌生及扩展的影响。结果表明,热疲劳裂纹优先在硬质相区中萌生、扩展,钢基体相阻碍裂纹的萌生及扩展。改善显微组织结构,可提高合金的抗热疲劳性能 相似文献
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针对异型坯连铸过程中出现较多表面纵裂的问题,使用有限元软件ABAQUS建立铸坯二维微段模型,使用Fortran语言编写表面热流子程序DFLUX模拟铸坯在结晶器内的凝固传热过程,使用接触算法与重启动技术分析铸坯在热应力、表面摩擦力及钢水静压力下坯壳的受力状态。结合材料力学属性分析得出,[R]角、腹板中心、翼缘中心与窄面中心位置为异型坯表面纵裂纹最易萌生区域,[其中R]角处距离弯月面约200 mm处更容易萌生表面纵裂纹,腹板、翼缘中心与窄面中心距离弯月面180 mm处更容易萌生表面纵裂纹。 相似文献
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Thermal fatigue test has been carried out on widely used hot work steel 4Cr5MoSiVl and a low alloyed steel 3Cr3MoV in temperature range of 200 to 700 °C. Tempering resistance, as well as high temperature hardness/strength of steel specimens, works as a dominating material parameter on thermal fatigue resistance. During the heating period, high hardness can depress the inelastic deformation. This deformation is the origination of tensile stress, which acts as the driving force of heat checking during the cooling period. The cyclic strain-oxidation interaction can speed up the damage on surface defects, which plays an obvious role in initiation of thermal cracks. On 4Cr5MoSiVl steel specimens, borders between the matrix and inclusions such as titanium compounds, or lager carbides such as primary carbides, are focused by strain and attacked by oxidation, and are main initiating places of cracks. While on 3Cr3MoV steel specimens, larger strain causes plastic deformation concentrating around grain boundaries. Then the following oxidation accelerates this grain boundary damage and creates cracks. 相似文献
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钴磷镀层表面热疲劳裂纹的萌生及扩展机理 总被引:2,自引:0,他引:2
在自约束型热疲劳试验机上对化学镀钴磷合金镀层进行了热疲劳试验,采用光学显微镜、扫描电子显微镜研究了在热应力作用下镀层表面热疲劳裂纹萌生、扩展的方式和形态。结果表明:200次冷热循环后,V型缺口处发生塑性变形,并且随冷热循环的进行,热疲劳裂纹由缺口底部萌生并沿着循环方向扩展。重点分析了钴磷合金镀层表面热疲劳裂纹的萌生及扩展机理。 相似文献
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The effect of rare earth elements on the thermal cracking resistance of high speed steel (HSS) rolls was investigated. Laser rapid heating was used for thermal fatigue experiments. Thermal cracks and microstructure were observed using metalloscopy and scanning electron microscopy. The results showed that thermal cracks initiated from the interface between the matrix and eutectic carbides (including M6C and M7C3 type carbides),and propagated along the interface between the two phases. MC type carbides enriched with vanadium could prevent the propagation of thermal cracks. The presence of rare earth elements decreased the quantity of big eutectic carbides,and proportionally increased spherical and rod-shaped MC type carbide content. HSS0 (0.00% RE) had approximately three times the thermal cracking density of HSS3 (0.12 wt.% RE). Rare earth elements were shown to significantly improve the microstructure and thermal cracking resistance of HSS rolls. 相似文献