外文翻譯--機(jī)械性能試驗(yàn)-拉伸試驗(yàn)和其他基本測試

原文： Mechanical Testing : tension Test and Other Basic Tests 4.1 INTRODUCTION 4.2 INTRODUCTION TO TENSION TEST 4.3 ENGINEERING STRESS STRAIN PROPERTILES 4.4 TRENDS IN TENSILE BEHAVIOR 4.5 TRUE STRESS STRAIN INTERPRETATION OF TENSION TEST 4.6 CMPRESSION TEST 4.7 HARDNESS TESTS 4.8 NOTCH-IMPACT TESTS 4.9 BENDING AND TORSION TESTS 4.10 SUMMARY OBJECTIVES Become familiar with the basic types of mechanical tests, including tests in tension compression, indentation hardness , notch impact, bending ,and torsion . Analyze date from tension tests to determine materials properties, including both engineering properties and true stress-strain properties . Understand the significance of the properties obtained from basic mechanical tests, and explore some of the major trends in behavior that are seen in these tests. 4.1 INTRODUCTION Samples of engineering materials are subjected to a wide variety of mechanical tests to measure their strength or other properties of interest .Such samples, called specimens, are often broken or grossly deformed in testing. Some of the common forms of test specimen and loading situation are (a). Compression tests (b) are also common. In engineering, hardness is usually defined in terms of resistance of the material to penetration by a hard ball or point, as in (c). Various forms of bending test are also often used ,as is torsion of cylindrical rods or tubes. The simplest test specimens are smooth (unnotched) ones, as illustrated in Fig.4.2(a). More complex geometries can be used to produce conditions resembling those in actual engineering Components, Notches that have a definite radius at the end may be machined into test specimens, as in (b). The term notch is used here in a generic manner to indicate any notch , hole , groove , slot ,etc., that has the effect of a stress raiser . Sharp notches that behave similar to cracks are also used, as well as actual cracks that are introduced into the specimen prior to testing ,as in (c) . Figure 4.1 Geometry and loading situations commonly employed in mechanical testing of materials (a) tension,(b) compression, (c) indentation hardness,(d)cantilever bending,(e) three-point bending,(f) four-point bending, and (g) torsion Figure 4.2 Three classes of test specimen : (a) smooth or unnotched, (b) notched ,and (c) precracked . To understand mechanical testing, it is first necessary to briefly consider materials testing equipment and standard test methods. We will then discuss tests involving tension , compression, indentation, notch impact ,bending, and torsion .Various more specialized tests are discussed in later chapters in connection with such topics as brittle fracture ,fatigue, and creep. 4.2 INERODUCTION TO TENSION TEST A tension test consists of slowly pulling a sample of material with an axial force, as in Fig 4.1(a), until it breaks. This section of the chapter provides an introduction to the methodology for tension tests, as well as some additional comments. Sections that follow discuss tension testing in more detail, after which other types of test are considered. Figure4.5 ensile specimens of metals(left to right): untested specimen with 9 mm diameter test section, and broken specimens of gray cast iron ,aluminum alloy 70575-T651,and hot-rolled AISI 1020 steel.(Photo by R.A simonds.) 4.2.1 Test Methodology The test specimen used may have either a circular or a rectangular cross section, and its ends are usually enlarged to provide extra area for gripping and to avoid having the sample break where it is being gripped. Specimens both before and after testing are shown for several metals and polymers in Fig.4.5 and 4.6. Methods of gripping the ends vary with specimen geometry. A typical arrangement for threaded-end specimens id shown in Fig.4.7.Note that spherical bearings are used at each end to provide a pure tensile force, with no undesirable bending. The usual manner of conducting the test is to deform the specimen at a constant speed. For example, in the universal testing machines of Fig.4.3, the motion between the fixed and moving crossheads can be controlled at a constant speed. Hence, distance h in Fig.4.7 is varied so that The axial force that must be applied to achieve this displacement rate varies as the test proceeds. This force P may be divided by the cross-sectional area Ai to obtain the stress in the specimen at Any time during the test: Figure4.6 Tensile specimens of polymers (left to right): Untested specimen with a 7.6 mm diameter test section, a partially tested specimen of high-density polyethylene (HDPE), and broken specimens of nylon 101 and Teflon (PTFE). (photo by R.A.Simonds.) Displacements in the specimen are measured within a straight central portion of constant cross section over a gage length li, as indicated in Fig.4.7.Strain be computed from the change in this length ,L； 錯誤 !未找到引用源。 4.2 Stress and strain, based on the initial (undeformed) dimensions, Ai and Li, as just presented, are called engineering stress and strain. Figure 4.7 typical grips for a tension test in a universal testing machine.( adapted from AMST 97 Std.E8；copyright C ASTM； reprinted with permission.) It is sometimes reasonable to assume that all of the grip parts and the specimen ends are nearly rigid .In this case ,virtually all of the change in crosshead motion is due to deformation within the straight section of the test specimen, so that L is approximately the same as h, the change In h ,strain may therefore be estimated as =h/li, However, actual measurement of L is preferable. Strain as calculate from Eq.4.2 is dimensionless. As a convenience, strains are sometimes given as percentages, where %=100.Strain may also be expressed in millionths, called microstrain, where u=100. If strains are given as percentages or as percentages or as microstrain , then, prior to using the value for most calculations, it is necessary to convert to the dimensionless from . The principal result obtained from a tension test is a graph of engineering stress versus engineering strain for the entire test, called a stress-strain curve. With the use of digital computers in the laboratory ,the form of date is a list of numerical values of stress and strain, as sampled at short time intervals during the test. Stress-strain curves vary widely for different materials. Brittle behavior in a tension test is failure without extensive deformation. Gray cast iron, glass, and some polymers, such as PMMA (acrylic), are examples of materials with such behavior. A stress-strain curve for gray iron is shown in Fig.4.8.Othermaterials exhibit ductile behavior, failing in tension only after extensive deformation. Stress-strain curves for ductile behavior in engineering metals and some polymers are similar to Figs. 4.9 and 4.10,respectively. Figure4.8 Stress-strain curve for gray cast iron in tension, showing brittle behavior. Figure4.9 schematic of the engineering stress-strain curve of a typical ductile metal that exhibits necking behavior. Necking begins at the ultimate stress point. 譯文 ： 機(jī)械性能試驗(yàn)：拉伸試驗(yàn)和其他基本測試 4.1 引言 4.2 拉伸試驗(yàn)介紹 4.3 工程應(yīng)力應(yīng)變特性 4.4 拉伸行為趨勢 4.5 拉伸試驗(yàn)的真實(shí)應(yīng)力應(yīng)變解釋 4.6 壓縮試驗(yàn) 4.7 硬度試驗(yàn) 4.8 抗缺口沖擊試驗(yàn) 4.9 點(diǎn)彎曲和扭轉(zhuǎn)試驗(yàn) 4.10 概要 目 標(biāo)： 熟悉機(jī)械試驗(yàn)的基本類型 ，包括拉壓、 壓痕硬度 、 抗缺口沖擊 、 彎曲和扭轉(zhuǎn)試驗(yàn)。 分析拉伸試驗(yàn)的數(shù)據(jù)來確定材料的性能，包括 工程特性與真實(shí)應(yīng)力 -應(yīng)變特性。 從基本力學(xué)試驗(yàn)中了解性能實(shí)驗(yàn)的意義，以及從這些試驗(yàn)中探索 一些行為中的主要趨勢 。 4.1 引言 材料的樣 品往往要進(jìn)行各種各樣的機(jī)械試驗(yàn)，以衡量他們的強(qiáng)度、性能之間的厲害關(guān)系。這樣的樣品，稱為標(biāo)本，這些樣本在試驗(yàn)中經(jīng)常被破壞或者嚴(yán)重變形。一些常見形式的試驗(yàn)樣品和載荷情況如（ a）所示。（ b）情況在壓縮試驗(yàn)中也很常見。在工程中，硬度通常被定義為材料的抗?jié)B透硬質(zhì)球或點(diǎn)，如（ c）所示。扭轉(zhuǎn)圓柱棒或管在各種形式的彎曲試驗(yàn)也經(jīng)常使用。 最簡單的試樣是光滑的（無缺口），如 圖 4.2（ a） 所示 。 更復(fù)雜的幾何形狀可以用來生產(chǎn)類似那些在實(shí)際工程元件軸凹口具有一定半徑的端部的情況，可被加工成如（ b）所示的試樣。凹口這個術(shù)語在這里是對所 有切口，孔，槽，縫隙等籠統(tǒng)的表示，這些都是由于應(yīng)力集中所帶來的影響。鋒利的凹口表現(xiàn)為類似于裂紋的被使用， 實(shí)際的裂紋被引入到測試前 的樣品中，如（ c）所示。 圖 4.1 圖 4.1 中的幾何和載荷情況是 在材料力學(xué)性能測試 中普遍采用，有（ a）拉伸，（ b）壓縮，（ c）壓痕硬度，（ d）懸臂彎曲，（ e）三點(diǎn)彎曲， (f)四點(diǎn)彎曲以及（ g）扭轉(zhuǎn) 圖 4.2 試驗(yàn)樣品 圖 4.2 中的三類試驗(yàn)樣品為（ a）光滑或無缺口樣品，（ b）有缺口樣品以及（ c）預(yù)制裂紋樣品。 要了解機(jī)械測試，首先有必要簡要地研究材料 試驗(yàn)設(shè)備和標(biāo)準(zhǔn)試驗(yàn)方法。然后，我們將討論包括拉伸，壓縮，壓痕，缺口沖擊，彎曲和扭轉(zhuǎn)測試。各種更專業(yè)的測試將在后面的章節(jié)中有討論，這樣的課題有脆斷裂，疲勞和蠕變。 4.2 拉伸試驗(yàn)介紹 拉伸試驗(yàn)包括在一個軸向力方向慢慢提拉材料試樣直到其斷裂，如圖 4.1（ a）所示。本章節(jié)將介紹進(jìn)行拉伸試驗(yàn)的方法，以及一些附加注解。跟隨討論更詳細(xì)的拉力試驗(yàn)，之后在考慮其他的測試。 圖 4.5 拉伸試樣金屬 圖 4.5 所示為 拉伸試樣的金屬（左到右） ： 未經(jīng) 測試 的 9 毫米直徑的測試 段試樣， 破壞 的灰鑄鐵標(biāo)本 ， 70575-T651 鋁合金和 AISI1020 熱軋鋼（圖片由R.A.Simonds.提供。） 4.2.1 測試方法 所使用的試樣可以是圓形或矩形的橫截面，其兩端通常需要加粗來為夾持提供額外的面積，以避免樣本在被夾持處斷裂。圖 .4.5 和 4.6 中的多種金屬和聚合物所示為測試之前和之后的兩個樣品。 試樣的幾何形狀不同抓住兩端的方式也有所不同。螺紋端的典型布置 id 標(biāo)本試樣如圖 4.7 所示。需要注意的是球軸承主要用在每個末端，以提供純粹拉伸力，沒有不需要的彎曲。 通常進(jìn)行 的 測試 方式 是在一個恒定的速度 下 變形試樣 。例如圖 4.3 中的萬能試驗(yàn)機(jī)固定和移動十字頭 之間的運(yùn)動可以以恒定的速度控制。因此，在圖 4.7 的距離 h 的變化，滿足 必須施加以達(dá)到這個位移速率變化的軸向力作為測試所得。這個力 P 可以表示為截面積