Biaxial Stress Measurement by Electrodeposited Copper Foil with Circular Holes
Biaxial Stress Measurement by Electrodeposited Copper Foil with Circular Holes
复制标题
圆孔电解铜箔双轴应力测量
DOI：
10.1111/j.1475-1305.2006.00249.x
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发表时间：
2006
期刊：
影响因子：
2.1
通讯作者：
Y. Ono
中科院分区：
文献类型：
--
作者：
S. Kitaoka;Y. Ono
电镀铜[1-8]是一种实验应力分析技术，用于测量部件在重复载荷作用下的表面应力。由于该方法利用沉积层中的晶粒生长，因此不需要输出部分，如电阻应变计的引线。因此，这种方法在应用于密封外壳中的机械元件时具有优势。已经认识到，在铜箔中晶粒的生长取决于剪切应力的幅值。参考文献[3]考虑了剪切应力主导晶粒生长的原因，证实了循环加载后铜箔表面形成滑移带。通过电化学抛光和蚀刻，证实了滑移带的生成位置与铜箔中生长晶粒的位置基本一致。由于在材料疲劳过程的初始阶段，最大剪应力分量负责滑带的形成，因此可以认为剪应力幅值主导晶粒生长。如果被测物体的弹性模量不同，在相同的剪应力下，表面的应变也不同。因此，产生生长晶粒的范围通常用应变分量而不是应力来表示。晶粒生长所需的剪切应变幅值约为0.9 ~ 1.8·10[1,2]，而镀铜方法的适用温度为80℃以下，因为在130℃·1 h[3]左右可以完美地产生热再结晶。由于在机器元件上电镀铜只能在易于电镀的材料上进行，因此通常采用将电镀铜箔粘附在机器元件上的方法。校准是任何镀铜方法的第一步。然后，使用与校准试验相同的电镀条件或将电沉积的质量相同的铜箔粘附到用于校准试验的箔上，进行实际试验。可以通过将结果与校准试验进行比较来测量应力。由于铜箔可以大批量生产，因此可以方便地使用同一块铜箔进行校准和应力分析测试，从而避免了该技术电镀版本可能出现的电镀溶液和条件的细微差异所带来的问题。由于在铜箔中生长的晶粒取决于剪应力的幅值，所以不可能测量双轴应力状态下机械元件的每个主应力。这严重制约了镀铜方法的应用。为了克服这个问题，作者开发了一种利用电沉积铜箔微孔[10]的新方法。该方法研究了循环加载过程中微圆孔外围滑移带形成的现象。在孔的边缘有四个位置，应力在纯剪切作用下达到最大值，在其他组合应力作用下有两个位置应力达到最大值。滑移带形成发生在这些位置。然而，当铜箔上形成多个圆孔时，由于最大应力集中位置的应变值在微观上不同，每个孔开始出现滑移带的应力与循环次数之间的关系是不同的。因此，在检查滑移带形成时，有必要对许多圆孔使用统计技术。主应力（r1, r2）是利用在孔边缘形成滑移带的点数与在孔边缘形成最大应力的点数之比以及在铜箔本身生长的晶粒密度[10]来确定的。然而，为了提高测量精度，必须观察到许多微圆孔，因此需要更大的测量区域。在本报告中，作者开发了新的双轴应力测量方法，该方法可以比上述方法使用更少的孔数来测量主应力[10]。众所周知，圆形周围的应力分布
Copper electroplating [1–8] is an experimental stress analysis technique that measures the surface stress of a component subjected to repeated loads. As this method utilises grain growth in the deposited layer, an output part, like a lead wire of an electrical resistance strain gauge, is not necessary. Thus, this method has an advantage when applied to machine elements in sealed casings. It has been recognised that the grains grown in copper foil depend on the shearing stress amplitude. The reason why the shearing stress dominates the grain growth is considered in Ref. [3], which confirms the formation of slip-band in the surface of the copper foil after cyclic loading. It has also been confirmed that the generated position of slip-bands almost corresponds to the position of grown grains in the copper foil, as revealed by electrochemical polishing and etching. As the maximum shearing stress component is responsible for the formation of slipbands at the initial stage of the material fatigue process [9], it is considered that the shearing stress amplitude dominates grain growth. If the modulus of elasticity of the measured object is different, the strain of the surface is different for the identical shearing stress. Therefore, the range in which the grown grains are generated is generally expressed in strain components rather than stress. The shearing strain amplitude necessary for grains to grow is about 0.9–1.8 · 10 [1, 2] and the temperature at which the copper electroplating method can be applied is below 80 C, because the thermal recrystallization is perfectly generated at about 130 C · 1 h [3]. As electroplating copper to a machine element can only be performed to a material which is easily electroplated, adhering the electrodeposited copper foil to the machine element is generally utilised. Calibration is the first stage in any copper electroplating method. Then, the actual test is carried out by using the same electroplating conditions as the calibration test or by adhering electrodeposited copper foil of equal quality to the foil used for the calibration test. It is possible to measure stresses by comparing results with the calibration test. As copper foil can be produced in large pieces, it is easy to use the same piece of foil for both calibration and the stress analysis test, thereby avoiding the problems caused by slight differences in plating solution and condition that can occur in the electroplating version of this technique. It is impossible to measure each principal stress of the machine element in a biaxial stress state because the grains grown in copper foil depend on the shearing stress amplitude. This seriously restricts the applications of the copper electroplating method. To overcome this, the authors have developed a new method that utilises electrodeposited copper foil with microcircular holes [10]. This method examines the phenomenon of slip-band formation at the periphery of microcircular holes during cyclic loading. There are four locations at the edge of a hole where stress becomes a maximum in pure shear and two locations where stress becomes a maximum in the other combined stress. Slip-band formation occurs in these locations. However, when multiple circular holes were formed in the copper foil, the relationship between the stress at which slip bands begin to occur and the number of cycles is different for each individual hole, as strain values at the maximum stress concentration locations are microscopically different. Therefore, it is necessary to use a statistical technique for many circular holes, when examining slip-band formation. The principal stresses (r1, r2) are determined using the ratio of the number of points at hole edges at which slip-bands form to the number of points at hole edges at which stress becomes maximum in addition to the density of the grains grown in the copper foil itself [10]. However, as many microcircular holes must be observed to improve measurement accuracy, and a larger measurement region is required for this. In this report, the authors developed the new biaxial stress measurement method which can measure principal stresses by using much fewer holes than the above-mentioned method [10]. It is well known that the stress distribution around the circular