One of the questions our applications team is most commonly asked is “Why aren’t my systems producing the exact same results?” Over years of applications consulting, we have found that optimizing the test configuration by instructing labs to use the same method files, implement standard operating procedures (SOPs) and use equivalent test setups is the best way to minimize test result differences. However, application engineers can only do so much as differences do exist in the real world. For example, every mechanical testing system is different, laboratories have different operators using their systems, different samples are actually being tested, and each specimen being tested is prepared with slight differences. There are many sources and reasons that may cause these differences and the sum of the differences may produce an overall error in the test results. Sources of error specific to materials testing are summarized in Figure 1.
While most users of materials testing equipment can understand these sources of error and do their best to minimize testing errors, eliminating error altogether is not possible. As companies grow, it is even more difficult to reduce sources of error between multiple test systems, multiple laboratories, and multiple geographic locations. Since error can never be eliminated, the next best option quality professionals have is to understand and quantify the error. One approach to both quantify and understand sources of error is to perform a gage repeatability and reliability (GR&R) study on a measurement system.