数字图像相关的中间应变率材料表征
Summary
本文提出了一种利用高速伺服-液压载荷框架对中间应变率拉伸试样进行动态表征的方法。还定义了应变计检测和分析的程序, 以及样品上的数字图像相关应变测量程序。
Abstract
材料在动态载荷作用下的机械响应通常不同于在静态条件下的行为;因此, 用于材料表征的常用准静态设备和程序不适用于动态载荷下的材料。材料的动态响应取决于其变形率, 大致分为高 (即大于 200s)、中间 (即 10−200/s) 和低应变率 (即小于 10/)。每一种制度都要求有具体的设施和测试协议, 以确保所获得数据的可靠性。由于使用高速伺服液压设备和经过验证的测试协议的机会有限, 在中间应变速率下, 结果存在明显差距。目前的手稿提出了一个验证的协议, 在这些中间应变速率的不同材料的表征。应变计仪器和数字图像相关协议也包括作为免费模块, 从每一个测试中提取最高水平的详细数据。介绍了从各种材料和试验装置 (如拉伸和剪切) 获得的原始数据的实例, 并介绍了用于处理输出数据的分析程序。最后, 讨论了使用现行协议进行动态表征的挑战, 以及设施的局限性和克服潜在问题的方法。
Introduction
大多数材料在其力学行为1中都显示出一定程度的应变率依赖性, 因此, 仅在准静态应变速率下进行的机械测试不适合确定动态的材料性能应用。通常使用五种类型的机械测试系统来研究材料的应变率依赖性: 传统的螺杆驱动负载框架、伺服液压系统、高速伺服液压系统、冲击测试仪和 hopkinson 杆系统1. 在过去50年里, 拆分的 hopkinson 条一直是材料动态表征的共同设施 2。还努力修改 hopkinson 柱, 以中等和较低的应变率进行测试。然而, 这些设施通常更适合于材料的高应变率特征 (即通常大于 200s)。在10−200/s 范围内 (即从拆分 hopkinson 3 获得的准静态和高应变率结果) 中, 关于材料性能的应变率特征存在差距 (即从拆分 hopkinson 3 获得的准静态应变率和高应变率结果), 这是由于进入设施的机会有限, 缺乏可靠的中间应变率材料测试程序。
高速伺服液压负载框架以恒定和预定义的速度将载荷施加到试样上。这些负载框架受益于松弛适配器, 在拉伸试验中, 该适配器允许横梁在加载开始前达到所需的速度。松弛适配器允许头部在一定距离 (例如0.1 米) 内行驶, 以达到目标速度, 然后开始将载荷施加到试样上。高速伺服液压负载框架通常在位移控制模式下进行测试, 并保持恒定的执行器速度, 以产生恒定的工程应变速率3。
测量试样伸长率的技术一般分为接触技术或非接触技术4。接触技术包括使用夹式扩展器等仪器, 而激光扩展器则用于非接触式测量。由于接触扩展器容易受到惯性的影响, 因此不适合动态测试;非接触式扩展器不会受到此问题的影响。
数字图像相关性 (dic) 是一种光学、非接触式、全场应变测量技术, 是一种用于应变测量的替代方法, 用于测量应变载荷并克服与之相关的一些挑战 (例如, 响铃现象)。动态材料特性5。电阻应变片可能会受到一些限制, 例如测量范围有限、伸长率范围有限和安装方法有限, 而 dic 始终能够在测量过程中从试样表面提供全场应变测量。实验。
所介绍的程序描述了使用高速伺服液压负载框架与 dic 一起, 并可作为补充文件, 以澄清最近制定的标准准则6 , 以澄清实验过程的细节。伺服-液压载荷框架上的部分可以遵循各种测试设置 (例如, 拉伸、压缩和剪切), 甚至可以使用普通的准静态载荷框架, 因此涵盖了广泛的设施。此外, dic 部分可单独应用于任何类型的机械或热测试, 但只需稍作修改。
Protocol
Representative Results
Discussion
从实验中获得的原始数据受试样几何形状和应变片在试样上的位置的影响。在较高应变速率下, 压电负载垫圈在负载框架中获得的低应变率动态测试中的负载数据 (bruce等人).建议>, 而王等人则建议。9报告此限制为 100/) 通常由于与加载相关的动态波而受到较大的振幅振荡。如图 1所示, 由于噪声水平高, 试样材料、?…
Declarações
The authors have nothing to disclose.
Acknowledgements
提交人承认 d买卖部、michel delonyy、tyler musclow、fraser kirby、joshua ilse 和 alex naftel 提供的巨大帮助。还感谢加拿大国家研究理事会 (nrc) 通过安全材料技术 (smt) 方案提供的财政支持。
Materials
| Camera Lens | Opto Engineering | Telecentric lens 23-64 | |
| High Speed Camera | SAX Photron Fastcam | ||
| High Speed DAQ | National Instruments | USB-6259 | |
| High Speed Servo-Hydraulic Load Frame | MTS Systems Corporation | Custom Built | |
| Jab Bullet Light with diffuser | AADyn JAB BULLET | 15° diffusers | |
| Strain gauge | Micro-Measurements | Model EA-13-062AQ-350 |
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