[论文解读] The Relation Between Wear and Irreversible Entropy Generation in the Dry Sliding of Metals

Hisham A. Abdel-Aal|arXiv (Cornell University)|Aug 2, 2010

Mechanical stress and fatigue analysis参考文献 22被引用 3

一句话总结

本文提出一种热力学模型，将干滑动金属的磨损与材料凸起区（MAZ）内不可逆熵产生联系起来，将MAZ视为类似卡诺热机的系统。研究发现，磨损速率与熵产生和熵流相关，铜与钛的磨损速率表现出相反趋势：质量磨损率与比磨损率随熵产生变化趋势相反；而残余熵比可预测磨损行为：熵传输过剩会加剧磨损，而熵产生则通过系统重新平衡机制降低磨损。

ABSTRACT

We examine the relationship between wear and the generation of entropy in dry sliding of metals. It is postulated that wear is related to irreversible entropy generation within the MAZ. We present a model, that treats the MAZ as a heat engine in the Carnot sense. The model assumes that the MAZ is a heat engine that transports heat from a high temperature reservoir, represented by the asperity contact layer, to a low temperature reservoir, represented by the sub-contact layer. Consequently an entropy generation source that represents the irreversibilities within the MAZ is defined and a study of the entropy generation is attempted. Wear data, published elsewhere, of two materials, Oxygen Free High conductivity Copper, and Commercially Pure Titanium are analyzed using the developed model. It is found that wear for both materials is correlated to entropy generation, and to the entropy flow within the MAZ. Interestingly, moreover, in view of the contrasting wear trends of the test materials, the relationship of the mass wear rate and the specific wear rate of each material with respect to entropy generation are totally opposite to each other. A common feature between the behavior of the two materials, was found in wear behavior with respect to a so called Ratio of Residual Entropy. This ratio determines wether the system is over or under supplied with entropy. It is found that when the capacity to transport entropy exceeds the entropy supply the mass wear rate increases, and when the entropy transport capacity of the system is exceeded and entropy generation takes place the mass wear rate decreases. This is attributed to the re-establishment of equilibrium within the system.

研究动机与目标

• 利用熵产生原理，探究干滑动金属磨损的热力学基础。
• 将材料凸起区（MAZ）建模为热机，以分析熵传输与不可逆性。
• 通过残余熵比相关联熵流与熵产生，建立磨损行为与熵动态的关联。
• 解释无氧高电导率铜与工业纯钛之间磨损趋势的差异。
• 识别熵传输能力或熵产生主导磨损响应的条件。

提出的方法

• 将MAZ建模为卡诺热机，将热量从凸起接触层（热源）传递至亚接触层（冷源）。
• 引入熵产生源项，表征MAZ内部的不可逆性。
• 利用无氧高电导率铜与工业纯钛的公开实验磨损数据验证模型。
• 引入“残余熵比”以量化系统在熵传输能力上是否过剩或不足。
• 分析质量磨损率与比磨损率随熵产生和熵流的变化关系。
• 应用热力学平衡原理，基于熵动态解释磨损率变化。

实验结果

研究问题

• RQ1 干滑动金属中的磨损如何与材料凸起区内的不可逆熵产生相关？
• RQ2 MAZ能否被建模为热力学热机以解释磨损行为？
• RQ3 为何质量磨损率与比磨损率在不同材料中随熵产生表现出相反趋势？
• RQ4 残余熵比在决定磨损率趋势中起何种作用？
• RQ5 由于熵产生引发的系统重新平衡如何影响磨损率？

主要发现

• 无氧高电导率铜与工业纯钛的磨损均与MAZ内熵产生和熵流相关。
• 当熵传输能力超过供给时，质量磨损率上升，表明系统存在过载能力。
• 当熵产生超过传输能力时，质量磨损率下降，表明系统通过重新平衡机制降低了磨损。
• 比磨损率随熵产生变化的趋势与质量磨损率相反，表明其具有不同的尺度行为。
• 两种材料的共同特征是：当熵供给与传输能力在残余熵比定义下达到平衡时，磨损最小化。
• 残余熵比具有预测作用：熵传输能力过剩会加剧磨损，而熵产生则通过热力学平衡恢复机制降低磨损。