NASA曾评估航天飞机推进系统中使用的流衬套,以确定振动是否会导致开裂。 由于衬套工作时可能受到一定范围的振动频率的影响,而哪种频率下会产生最大的振动应变是未知的。

A flow liner used in the propulsion system on the space shuttle was under evaluation to determine whether vibrations could result in cracking. The liner could be subject to a range of vibration frequencies, and it was not known which would produce the greatest vibratory strains.

 

技术挑战 Challenges

 
flowliner1

被测试件很复杂,这意味着该部件的整体响应将无法预测。 由于它结构自重很低,这意味着与试件的任何接触都可能会改变其力学响应。 虽然主要关注的领域不是很大,但它的结构具有几何特征,这使得难以预测峰值应变的位置。 也很难知道峰值应变的区域是否足够大,是否可用应变片进行识别。 加之需要模拟飞行条件所需的高频率,使测试更加复杂。 测试最终需在高达6kHz的频率下测量振动响应。

The specimen under test was complex, which meant that the overall response of the part would be impossible to predict. It was also fairly lightweight, which meant that any contact with the specimen could be expected to alter its response. Although the areas of primary concern were not very large, they included geometric features which made it difficult to predict the location of peak strains. It was also difficult to know whether the areas of peak strain would be large enough to be identified with strain gages. This test was further complicated by the high frequencies required to simulate flight conditions. Vibration response was measured at frequencies up to 6kHz.

 

解决办法 Solution

 
flowliner2

CSI公司提供了一套Vic-3D系统及振动同步模块,确保可以精确地从振动试件中采集数据,而且无需高速摄像机。 由于DIC测量不需要接触试件,因此试件的运动不受测量系统的影响。 在整个图像区域获得应变测量值,从而确定最大应变的真实位置。 由于Vic-3D具有很高的空间分辨率,即使峰值应变集中在很小的区域,研究人员也能够获得准确的测量结果。

Correlated Solutions provided a Vic-3D system and a vibration synchronization module designed to accurately capture data from vibrating specimens without the expense of high-speed cameras. Because the measurements do not require contact with the specimen, the specimen’s movement was not affected by the measurement system. Strain measurements were obtained over the entire image area, allowing the true location of the maximum strain to be identified. Because of Vic-3D’s  high spatial resolution, researchers were able to obtain accurate measurements even when peak strains were concentrated in a very small area.

 

                       
 

 

 

 

 

 

 

 

                 exx max=  ±200µε                                                                                                                        eyy max=  ±300µε

 

 

 

相关链接 Links

 

Click here to see an animation of the 3D plot shown above.

Read about the Vibration Fatigue Module for more information on this technology.