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.

每次做得好的應(yīng)變測量都應(yīng)將傳感器下部實(shí)際出現(xiàn)的應(yīng)變精確地表示出來。然而，作為測量應(yīng)變本身的手段去獲取應(yīng)變數(shù)據(jù)，卻是很少見的。應(yīng)變測量通常只不過是間接地獲得關(guān)于其他某個工程參數(shù)信息的方便工具。比如，在傳感器的彈性元件上進(jìn)行應(yīng)變測量時，其應(yīng)變數(shù)據(jù)一般用來確定實(shí)際產(chǎn)生這一應(yīng)變的力或位移或轉(zhuǎn)矩或加速度或其他變量的大小。在應(yīng)力分析工作中，測得的應(yīng)變通過應(yīng)力-應(yīng)變之間的內(nèi)在基本關(guān)系轉(zhuǎn)換成應(yīng)力。要是測量結(jié)果看上去是合理的，那么，應(yīng)變數(shù)據(jù)很少受到懷疑。但若碰到意外的結(jié)果，其應(yīng)變數(shù)據(jù)通常就成為首要的被懷疑對象。

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.

失望是期望過高的產(chǎn)物，試驗(yàn)結(jié)果也決不例外。建立在不合理的模型、承載條件和材料參數(shù)基礎(chǔ)上的預(yù)期值常會使好的試驗(yàn)數(shù)據(jù)看上去不好。將這種數(shù)據(jù)加以合理化，或?qū)⑵渫耆珤仐?，可以是一條簡易的脫身之計(jì)，這是支撐一個錯誤模型的方法。采取這種形式的自欺欺人的態(tài)度經(jīng)常會令人失望。

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.

意外的結(jié)果通?？梢詺w因于數(shù)學(xué)模型、材料的機(jī)械性能或?qū)嶋H試驗(yàn)。例如，在當(dāng)今掌握了有限元模擬能力的情況下，就比以往任何時候更容易產(chǎn)生不合理的模型?，F(xiàn)代復(fù)合材料對應(yīng)力-應(yīng)變內(nèi)在基本關(guān)系以及準(zhǔn)確了解材料性質(zhì)的重要性提出了新的要求。于是乎，就會經(jīng)常碰到測量數(shù)據(jù)以及數(shù)據(jù)分析的問題。

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.

同數(shù)學(xué)模型和理論關(guān)系式不同，試驗(yàn)數(shù)據(jù)是實(shí)實(shí)在在的。它的出現(xiàn)是因?yàn)榘l(fā)生了一些情況從而產(chǎn)生了它。數(shù)據(jù)是否準(zhǔn)確可能是唯一的問題。有素養(yǎng)的工程師認(rèn)為數(shù)據(jù)包含著許多測量誤差和不確定的東西。在將測量結(jié)果同預(yù)期值進(jìn)行比較之前，首先必須考慮這些因素。

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.

工程師的任務(wù)是把數(shù)據(jù)弄明白，特別當(dāng)數(shù)據(jù)令人失望時。采用的模型對不對?材料的性質(zhì)正確不正確?試件加載適當(dāng)不適當(dāng)？是否計(jì)及了所有重要的誤差源?被測應(yīng)變是否真是你認(rèn)為正在測的那個應(yīng)變？必定有些什么情況發(fā)生了。請相信數(shù)據(jù)。

責(zé)任編輯：admin