Applications of Strain Gradient Plasticity: Modeling and Experiments

应变梯度塑性的应用：建模和实验

• 批准号: 9610491
• 负责人: YongGang Huang
• 金额: $ 6.94万
• 依托单位: Michigan Technological University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 1997
• 资助国家: 美国
• 起止时间: 1997-04-01 至 1999-03-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9610491&HistoricalAwards=false
• 关键词: Applications; Strain; Gradient; Plasticity; Modeling

9610491 Huang Efficiency and effectiveness of numerous engineering applications (typically macroscale) are significantly influenced by the underlying microscale phenomena. Consequently, macroscale design considerations of engineering products and manufacturing processes require detailed microscale insights. Texture formation in bulk and sheet forming, shear banding (that essentially governs chip formation characteristics in machining), strength and toughness of particle/fiber reinforced composite materials, and mechanical properties of thin film interfaces are examples of this class of problems, A multi-scale representation capable of capturing the micro-scale effects and synthesizing its essence within the context of an otherwise macroscale model is necessary for effective consideration of such engineering problems. Moreover, interests in several microscale engineering problems, e.g., MEMS, nano- and sub-micron scale surface modification techniques in electronic packaging and failure of fine line interconnects in microelectronic circuits, have also increased significantly in recent years. Experimental observations (e.g., micro-indentation, torsion of thin wires, strength of thin films) show that material behavior at the microscale is significantly different from that at the macroscale. These microscale experiments also exhibit considerable influence of geometric parameters on material properties. Predictions based on conventional constitutive models fail to account for such microscale phenomena that may have profound implications in design and manufacturing of a wide spectrum of engineering devices. For example, the conventional plasticity theory cannot explain the increased hardness in micro-indentation tests as compared to macro- indentation of the same material. Material removal characteristic s in machining of metals are crucially dependent on the thickness of the generated shear band; conventional plasticity provides no direct avenue to estimate such parameters. The strain gradient plasticity recently proposed by Fleck and Hutchinson (1993) satisfies the Clausius-Duhem thermodynamic restrictions on the constitutive law for second deformation gradients, and is potentially capable of effectively probing micron and sub-micron scale material behavior. It can also provide an effective transition for incorporating the microscale effects within a generalized framework of plasticity. However, a material length scale is introduced in the strain gradient plasticity, and needs to be determined from a set of independent microscale experiments. Accordingly, the proposed work first focuses on developing- two independent sets of experiments: (1) bending of micron-thick Cu beams and plates using Atomic Force Microscopy, and (2) measurement of shear band thickness and sub-structures (in compression tests) using optical-, electron- and atomic force microscopy. Observations from these experiments, in conjunction with suitable modeling efforts, will provide independent estimates of the "material length scale". Comparison of these results with others will facilitate investigations of the validity of the "material length scale" as a material parameter. The experiments will also be used to (i) quantitatively estimate the material length scale for individual materials, and (ii) establish the region of interest of strain gradient theory for particular materials. We will then utilize the strain gradient plasticity theory to probe different engineering applications where microscale phenomena play important roles. In machining, we will directly estimate the shear band thickness for different FCC, BCC and HCP materials under va rious cutting conditions, and (i) validate predictions against observations from proposed machining- experiments; (ii) quantitatively investigate the influence of shear band thickness on quality and integrity of the finished surface. For composites, we will investigate the influence of particle/fiber size on effective strength. Micro-mechanical sensors, actuators and transducers commonly use thin film bi-layers (thin film on thin film). We will carry out modeling- and experimentation on such systems.

9610491黄效率 和 众多有效 工程应用 （通常为宏观） 是 显著影响 通过 的 底层 微尺度 现象。 因此，委员会认为， 宏观尺度 设计 考虑 工程产品和制造过程的复杂性需要详细的微观洞察力。 块状和片状成形中的织构形成，剪切带（主要控制切屑形成 机械加工特性）、强度 颗粒/纤维增强复合材料的韧性和薄膜界面的机械性能是例子 的 这类问题， 一 多尺度表示能够捕捉微观尺度的影响，并综合其本质的背景下，否则 宏观尺度模型是必要的，以有效地考虑这些工程问题。 此外，在几个微尺度工程问题的兴趣，例如， 微机电系统， 电子封装中的纳米级和亚微米级表面改性技术以及细线互连的失效 在微电子电路中， 有 近年来也大幅增加。 实验 观察（例如， 微压痕，细线的扭转，薄膜的强度）表明，材料 微观尺度的行为是 这与宏观尺度上的差异很大。 这些微尺度实验也表现出相当大的影响几何参数对材料性能。 基于传统本构模型的预测不能解释这种微尺度现象，这种现象可能对宽范围的设计和制造产生深远的影响。 的 工程设备。 为 举例来说， 传统的塑性理论不能解释显微压痕试验中硬度比宏观压痕试验中硬度的增加 的 同样的材料。 材料 金属切削特性 是 关键取决于所产生的剪切带的厚度;常规塑性不能提供直接的 大道 来估计这些参数。 Fleck和哈钦森（1993）提出的应变梯度塑性理论满足Clausius-Duhem热力学对第二变形梯度本构律的限制，可以有效地研究微米和亚微米尺度的材料行为。 它也可以提供一个有效的过渡，将微尺度效应在一个广义的框架内的塑性。然而，在应变梯度塑性中引入了材料长度尺度，并且需要 确定 从一组独立的 微型实验 因此，建议首先 重点 两组独立的实验： (1)微米厚的铜梁和板的弯曲， 原子力显微镜和 (2)剪切带厚度和子结构的测量 (in压缩测试）使用光学，电子和 原子力显微镜 这些实验的观察结果，结合适当的 建模 努力，将 提供 对“物质长度尺度”的独立估计。 将这些结果与其他结果进行比较，将有助于研究“材料长度尺度”作为材料参数的有效性。 实验还将用于（i）定量估计材料长度尺度 为个别材料，和（ii）建立特定材料的应变梯度理论的感兴趣的区域。 然后，我们将利用应变梯度塑性理论来探讨不同的工程应用中的微尺度现象发挥重要作用。 在机械加工中，我们将直接估计不同FCC、BCC和HCP材料在各种切削条件下的剪切带厚度，并且（i）根据拟议的机械加工实验的观察结果验证预测;（ii）定量研究剪切带厚度对成品表面质量和完整性的影响。 对于复合材料，我们将研究颗粒/纤维尺寸对有效强度的影响。 微机械传感器、致动器和换能器通常使用薄膜双层（薄膜上薄膜）。 我们将对这种系统进行建模和实验。