A well-done strain measurement should produce an accurate representation of the strain actually present under the sensor. Strain data, however, is seldom gathered as a means unto itself. It is usually little more than a convenient vehicle for indirectly obtaining information about some other engineering parameter. When measured on a transducer spring element, for example, strain data is used to determine the magnitude of the force, displacement, torque, acceleration, or other variable actually producing the strain. In stress analysis work, the measured strains are converted to stresses through the stress-strain constitutive relationships. When the results seem reasonable, the strain data is seldom questioned. But when unexpected results are encountered, it is commonly made the primary suspect.
每次做得好的应变测量都应将传感器下部实际出现的应变精确地表示出来。然而，作为测量应变本身的手段去获取应变数据，却是很少见的。应变测量通常只不过是间接地获得关于其他某个工程参数信息的方便工具。比如，在传感器的弹性元件上进行应变测量时，其应变数据一般用来确定实际产生这一应变的力或位移或转矩或加速度或其他变量的大小。在应力分析工作中，测得的应变通过应力-应变之间的内在基本关系转换成应力。要是测量结果看上去是合理的，那么，应变数据很少受到怀疑。但若碰到意外的结果，其应变数据通常就成为首要的被怀疑对象。
Disappointment is the child of unreasonable expectations. Test results are no exception. Expectations based on unreasonable models, loading conditions, and materials parameters will always make good test data look bad. Rationalization of, or outright disregard for, the data can provide an easy out, a means for shoring up a faulty model. Practicing this form of self-deceit regularly disappoints.
失望是期望过高的产物，试验结果也决不例外。建立在不合理的模型、承载条件和材料参数基础上的预期值常会使好的试验数据看上去不好。将这种数据加以合理化，或将其完全抛弃，可以是一条简易的脱身之计，这是支撑一个错误模型的方法。采取这种形式的自欺欺人的态度经常会令人失望。
Unexpected results usually can be attributed to the mathematical model, the mechanics of materials, or the physical test. The production of unreasonable models, for example, is easier than ever with the availability of today's finite-element modeling capabilities. Modern composite materials place new demands on the stress-strain constitutive relationships and the importance of accurately knowing materials properties. And then there is always the measurement data and its interpretation.
意外的结果通常可以归因于数学模型、材料的机械性能或实际试验。例如，在当今掌握了有限元模拟能力的情况下，就比以往任何时候更容易产生不合理的模型。现代复合材料对应力-应变内在基本关系以及准确了解材料性质的重要性提出了新的要求。于是乎，就会经常碰到测量数据以及数据分析的问题。
Unlike mathematical models and relationships, test data is real. It came into being because Something Happened to produce it. Whether the data is accurate can be the only question. A good engineer assumes that it contains a number of measurement errors and uncertainties. These must be taken into account before the measurement results are compared against expectations.
同数学模型和理论关系式不同，试验数据是实实在在的。它的出现是因为发生了一些情况从而产生了它。数据是否准确可能是唯一的问题。有素养的工程师认为数据包含着许多测量误差和不确定的东西。在将测量结果同预期值进行比较之前，首先必须考虑这些因素。
The job of an engineer is to understand the data, especially when it disappoints. Is the model right? Are the materials properties correct? Is the test specimen properly loaded? Are all the important measurement error sources accounted for? Is the strain being measured actually the one the engineer thought was being measured? Something Happened. Believe the data.
工程师的任务是把数据弄明白，特别当数据令人失望时。采用的模型对不对?材料的性质正确不正确?试件加载适当不适当？是否计及了所有重要的误差源?被测应变是否真是你认为正在测的那个应变？必定有些什么情况发生了。请相信数据。
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