Analysis of Heat Flow Around Bolted Joints and Variations of Axial Bolt Force

Abstract

A bolted joint is widely used for the structures and machines subjected to thermal load, such as pressure vessels, internal combustion engines, brake disks, etc. In order to accurately evaluate the thermal stresses thus produced, the effect of thermal contact resistance at the interface and the heat flow through small gaps, which exist around the objective bolted joint, must be taken into account. In this paper, a numerical approach is proposed to solve the mechanical and thermal behaviors of bolted joints with high accuracy and computation efficiency, where empirical equations for thermal contact coefficient and apparent thermal contact coefficient are incorporated into commercial engineering software. By conducting systematic three-dimensional finite element analyses, it has been quantitatively elucidated how the supplied heat flows through each part of a bolted joint and how the axial bolt stress and bolt bending stress vary with time. It is concluded that bolted joints made of the materials with low thermal conductivity show specific heat flow patterns around the bolted joint and generate a large amount of variations in both axial bolt stress and bolt bending stress.

A novel piezoelectric dynamometer based on double-sensor for thermal compensation

“…According to the derived Ws, We-st, W , and s can be solved through numerical methods. According to the material parameters in Table 1 30 and W=500W/m3, the thermal force F T over time Δt curve in ordinary piezoelectric dynamometer is shown in Figure 2.

Figure 2.Thermal force F T over time Δt in ordinary piezoelectric dynamometer.

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Variation of Bolt Loads of Axle Braking Disc under Continuous Braking Condition

“…。高速 列车运行过程中，由于轮对磨损不均匀，车轮会呈 现出多边形的状态。这种多边形的轮对在钢轨上滚 动时会出现强烈的振动激扰，这种振动传递到轮轴 系统中的关键部件，使得这些部件及联接紧固结构 的可靠性承受严峻考验 [5] 。交变载荷的另一个来源 是制动时产生的热应力。由于螺栓连接通常是在室 温下完成组装，热载荷必然会造成螺栓载荷的演化 和交变 [6][7] 。制动盘在制动过程中，巨大的制动热负 荷使制动盘结构中产生很大的温度梯度，但由于受 制动盘的结构约束，制动盘内部包括螺栓连接会产 生热应力 [8][9][10][11] 。 断口照片(图 1b)进一步显示疲劳裂纹从裂纹源 开始沿与螺栓轴向成一定倾斜角的平面扩展。这表 明该裂纹为 I 型和 II 型的混合型裂纹，即该裂纹在 远场拉伸应力和剪切应力(由横力弯曲载荷导致)共 同作用下发生疲劳扩展。弯曲载荷的出现对于螺栓 来说是灾难性的。通常的螺栓强度校核规范中只考 虑螺栓的拉伸失效，对于螺栓的拉伸疲劳强度也有 相应的测试标准 [12][13] 。对于螺栓弯曲疲劳强度由于 缺乏通用的实验测试标准，螺栓抗弯曲疲劳的数据 比较缺乏 [14] 。由于制造工艺的限制，螺栓会不可避 免的存在制造缺陷，在长期的交变载荷的作用下， 这些薄弱部位可能会产生微裂纹并扩展，造成螺栓 的最终失效。但现阶段，国内外针对列车制动盘螺 栓失效的研究还比较少 [15][16] …”