了解复合材料压缩试验方法

Compression properties of composites are impacted by the resin and fiber resin interface, 并经常决定整体设计, 大小, 和零件的重量. Composite compression testing is crucial for screening new materials and maintaining quality control.   

The goal of a composite compression test is to drive compressive forces into a uniform gauge area without causing premature failure or improper failure modes in other parts of the specimen. 随着复合材料的不断进步, obtaining a universal standard for performing compression testing has presented challenges.  

综合测试 often follows ASTM or ISO methods, but organizations sometimes develop proprietary test methods. 不同的技术可能会产生不同的结果, so careful documentation of the test method and outcome is crucial in understanding the material properties. 

The existing composite compression test methods fall into three classes, 根据材料在测试架上的加载方式:

• 弯曲
• 剪切
• End-loaded

ASTM弯曲复合材料压缩试验 

ASTM D5467 and ASTM D7249 document two of the most common bending test methods for compressive properties of composites. 

弯曲加载采用夹层梁结构进行测试, 哪个面被压缩了, 对面的脸处于张力状态. The compressive face is generally constructed with a thinner facesheet so that the beam fails first in compression. 

在构建标本时, 跨越, 核心材料, 厚度, and adhesives are selected to ensure that the correct failure mode (compression facing) is achieved. Strain gauges on the compressive face are used to measure modulus, 泊松比, 紧张到失败.  

剪切加载压缩试验ASTM D3410

有些方法对试件的规范区域施加剪切载荷. 第一个方法之一, 通常称为塞拉尼斯压缩, loads the sample through wedges that are gripped by a cone-shaped fixture. 标本呈矩形，通常带有标签. Celanese compression was initially referred to in the ASTM D3410 standard but has since been removed. 塞拉尼斯的标本一般限于0.25英寸的宽度由ASTM标准和10mm的ISO 14126.  总长度是5.5英寸加0.5“无支撑长度. 

虽然塞拉尼斯压缩通常被认为是过时的, 有时需要与历史数据进行比较. 对于这种方法, material 厚度 is a critical consideration and must be within the narrow range specified, 怎样才能使楔与锥的位置合适呢. 

The current version of ASTM D3410 is commonly called the IITRI method, which was developed to mitigate some of the weaknesses in the Celanese method. The IITRI fixture is large and heavy, which presents challenges when used at extreme temperatures. 用于这种方法的样品可达1英寸宽和5英寸宽.5英寸长，0.5英寸无支撑长度. 楔形板通过矩形阀座加载, so the overall 厚度 of the specimen is not as critical as in the Celanese method. However, the material within the gauge area must be thick enough to preclude Euler buckling. Most data users agree that the test provides a compressive stress result because of the significant unsupported length in the material. 

末端加载压缩试验ASTM D695

Plastics have traditionally been tested using the end loading methods described in ASTM D695. This method allows for the end-loading of a prism that is square or round in cross-section. A dog-bone shaped flat specimen may also be used and is loaded in a side support fixture that precludes buckling.   

先进复合材料供应商协会, SACMA, adopted and formalized an industry practice of using tabbed specimens with a 0.188英寸轨距. The samples generally result in a higher apparent compressive strength because of the shorter gauge length. Since all these specimens are end-loaded, the ends must be flat and parallel for relevant results. If the specimens fail or broom at the ends, the results should be considered invalid.  

另外, if the level of torque applied to the bolts that secure specimen to the fixture is too high, 测试结果可能无效. Due to the short gauge length and the variability of friction from the side support fixture, 这种方法的进一步标准化进展缓慢.   

Combination of shear and end-loading compression testing ASTM D6641

Continued fixture development resulted in a combined loading compression fixture. ASTM D6641描述了适当的夹具和测试方法. 
与之前的方法一样，标称试样为5.5英寸长，带0.5英寸无支撑长度. 通过夹紧夹具的两端之间的方形两端, the specimen is loaded with a combination of end and shear loading. 

The combined loading compression fixture is smaller and easier to use than the IITRI fixture. Carefully torquing the fixture bolts to an even, specified level is essential. Specimens are strain gauged with back-to-back gauges to monitor for Euler buckling. The percent bending is reported with the test data and may be used to troubleshoot anomalous data.

For composite design, values for compression with a hole to simulate a stress riser is often needed. 裸眼压缩试验ASTM D6484 这样的方法可以获得这些值吗.

复合材料压缩试验方法比较 

结论 

Composite compression testing methods vary by fixture design, loading techniques, and specimen 大小. While there is no set standard for testing the compressive strength of composites, our experts can help you select the test methods that will generate the required result. im体育APP works diligently to make certain your composite materials are fit for purpose.

If you require composite compression testing or have questions about which methods are right for your material, 请 立即im体育APP.