材料的机械行为.ppt
CHAPTER 2Mechanical Behavior,Testing,and Manufacturing Properties of Materials材料的機械行為、測試及製造特性2021/9/231Working Medium of Manufacturing ProcesslForcelHeatlLightlAcoustics(聲音、音響)lElectricitylChemistrylBiology2021/9/232室溫時材料之相對機械性質(Relative Mechanical Properties of Materials at Room Temperature)2021/9/233Tensile-Test Specimen and Machine(b)Figure 2.1 (a)A standard tensile-test specimen before and after pulling,showing original and final gage lengths.(b)A typical tensile-testing machine.2021/9/234應力應變曲線（Stress-Strain Curve）Figure 2.2 A typical stress-strain curve obtained from a tension test,showing various features.P-；-彈性區經過放大斜率=E比例限、彈性限、降伏強度Offset=0.2%反覆循環負荷之曲線形狀曲線下面積材料韌性neckingE2021/9/235Eng.stressTrue.stressEng.strainTrue strainvTension Testll0AA0PNecking (Fig.2.2)Spring back(Fig.2.3)Engineering strain=True strain=Engineering stress=True stress=2021/9/236Loading and Unloading of Tensile-Test SpecimenFigure 2.3 Schematic illustration of the loading and the unloading of a tensile-test specimen.Note that,during unloading,the curve follows a path parallel to the original elastic slope.2021/9/237Mechanical Properties of Various Materials at Room Temperature2021/9/238ExmpleATrue stressTrue strainB利於進行製造的材料利於進行製造的材料:B B材質塑性區大，降伏強度低，較易進入加工區域。(然而A較易滿足設計需求，強度大)2021/9/239Ch 2.2.2 Ductility 延性Elongation=（伸長量）Reduction of area=（面積縮率、斷面縮率）2021/9/2310Elongation versus%Area ReductionFigure 2.4 Approximate relationship between elongation and tensile reduction of area for various groups of metals.2021/9/2311Ch 2.2.4 應力-應變曲線之建立Stress-strain curvesTrue strainTrue stressn:strain-hardening exponent(n=0，表示沒有加工硬化現象)2021/9/2312Typical Values for K and n at Room Temperature2021/9/2313各種不同金屬在常溫下的True Stress-True Strain CurvesFigure 2.6 True stress-true strain curves in tension at room temperature for various metals.The curves start at a finite level of stress:The elastic regions have too steep a slope to be shown in this figure,and so each curve starts at the yield stress,Y,of the material.2021/9/2314 Prove=n at neckingAt necking:NeckingUTSCh 2.2.5?e=2021/9/23152.2.6 溫度效應 Temperature Effects on Stress-Strain CurvesFigure 2.7 Typical effects of temperature on stress-strain curves.Note that temperature affects the modulus of elasticity,the yield stress,the ultimate tensile strength,and the toughness(area under the curve)of materials.T，則，則ductility，yield stress 和和 modulus of elasticity (因為因為T，原子動能原子動能，容易克服差排障礙容易克服差排障礙，延展性佳延展性佳)2021/9/2316表2.32.2.7變形速率的影響 Effect of Strain Rate on Ultimate Tensile Strength2021/9/23172.2.7變形速率的影響 Effect of Strain Rate on Ultimate Tensile StrengthFigure 2.8 The effect of strain rate on the ultimate tensile strength for aluminum.Note that,as the temperature increases,the slopes of the curves increase;thus,strength becomes more and more sensitive to strain rate as temperature increases.Source:J.H.Hollomon.strain rate tensile strength（應（應變硬化）變硬化）直線斜率直線斜率m：應變硬化應變硬化敏感度指數，敏感度指數，Temp m,m大可以延緩大可以延緩necking發生，應用在金屬薄板發生，應用在金屬薄板的成形。的成形。2021/9/23182.2.7變形速率的影響 Effect of Strain Rate on Ultimate Tensile Strength超塑性（superplasticity）:某些材料在拉伸試驗時，頸縮及破壞前，發生大量的均質伸長變形量，這種變形量從幾百個百分比到兩千個百分比之間。例如：口香糖、玻璃、熱塑性塑膠、Zn-Al合金及鈦合金。2021/9/2319壓力：幾個ATM到3.5GPa(500KST)，液壓增加時，材料破壞時的應變量會大量增加（不容易破壞）。脆性材料之金屬成形：液壓擠製、粉末冶脆性材料之金屬成形：液壓擠製、粉末冶金壓製。金壓製。當加工製造當加工製造stress超過材料破裂點超過材料破裂點，可使用下列方法避免：，可使用下列方法避免：l加溫加溫l加液靜壓加液靜壓(Hydrostatic Pressure Effect):脆性材料加脆性材料加工工2.2.8 靜液壓的影響（Hydrostatic pressure effects)2021/9/2320暴露在高能量輻射下：暴露在高能量輻射下：鋼料及其他種類金屬會發生降伏應力、抗拉強度及硬度會增加；延展性及韌性會減少。塑膠材料對其機械性質也有不好的影響。2.2.9 輻射的影響（Radition effects)2021/9/2321桶形失真（barreling）:摩擦力2.3 壓縮(Compression)2021/9/23222.3 壓縮(Compression)Figure 2.9 Disk test on a brittle material(陶陶瓷瓷、玻玻璃璃),showing the direction of loading and the fracture path.2021/9/23232.3 壓縮(Compression)蒲辛格效應（蒲辛格效應（Bauschinger effect 1881）:金屬受拉力進入到塑性狀態，將負荷釋放再施以壓縮應力，此時，壓縮的降伏應力值比拉伸時低許多。應變軟化（strain softening）、作工軟化（work softening）:因負荷的方向轉換，使降伏應力值下降。2021/9/23242.4 扭 轉(Torsion)Disk and Torsion-Test SpecimensFigure 2.10 Typical torsion-test specimen;it is mounted between the two heads of a testing machine and twisted.Note the shear deformation of an element in the reduced section of the specimen.2021/9/23252.5 彎曲（撓曲）Bending（Flexure）Figure 2.11 Two bend-test methods for brittle materials:(a)three-point bending;(b)four-point bending.The areas on the beams represent the bending-moment diagrams,described in texts on mechanics of solids.Note the region of constant maximum bending moment in(b);by contrast,the maximum bending moment occurs only at the center of the specimen in(a).硬脆材料通常都使用硬脆材料通常都使用bending實驗量測材料性實驗量測材料性質質(因為因為tension實驗不易進行實驗不易進行)2021/9/2326設備便宜且方便，所以產業界常用 Brinell(布氏硬度 1900):HB P對表面積的比值 Rockwell(洛氏硬度 1922):HR 深度 Vickers(維氏硬度 1922)：HV 深度 Knoop(克氏硬度)：HK Load極小(5-25kg)，做微硬度測試，可用於薄脆試件。Scleroscope(蕭氏硬度)：反跳高度、大面積 Mohs (莫氏硬度 1822)：互相摩擦，值1（滑 石）-10（鑽石）。Durometer 硬度測試計 Hot hardness 熱硬度 Ch 2.6 硬度（Hardness）2021/9/2327Hardness TestsFigure 2.12 General characteristics of hardness-testing methods and formulas for calculating hardness.The quantity P is the load applied.Source:H.W.Hayden,et al.,The Structure and Properties of Materials,Vol.III(John Wiley&Sons,1965).2021/9/2328Brinell Testing(c)Figure 2.13 Indentation geometry in Brinell testing;(a)annealed metal;(b)work-hardened metal;(c)deformation of mild steel under a spherical indenter.Note that the depth of the permanently deformed zone is about one order of magnitude larger than the depth of indentation.For a hardness test to be valid,this zone should be fully developed in the material.Source:M.C.Shaw and C.T.Yang.2021/9/23292021/9/2330Hardness Conversion ChartFigure 2.14 Chart for converting various hardness scales.Note the limited range of most scales.Because of the many factors involved,these conversions are approximate.硬度測試對照表硬度測試對照表lHRC機械工業常用機械工業常用(範圍對範圍對應應鋼鋼材材)lHRC55以上是很硬的鋼材以上是很硬的鋼材2021/9/2331Hardness is linearly proportional to Strength(UTS)UTS MPa=3.5(HB)Eq.(2.13)UTS psi=500(HB)Eq.(2.14)Ch 2.6.2 硬度和強度（Hardness and strength）2021/9/2332疲勞破壞：疲勞破壞：工件在未達到靜態負荷時的降伏應力下，發生破裂。金屬的疲勞限疲勞限與其極限抗拉強度（UTS）有關，鋼料約為1/2，鋁則無（以107）。如下圖2.152.7 疲勞（Fatigue）2021/9/23332.7 疲勞（Fatigue）S-N Curves2021/9/23342.7 疲勞（Fatigue）S-N CurvesFigure 2.15 Typical S-N curves for two metals.Note that,unlike steel,aluminum does not have an endurance limit.2021/9/2335Endurance Limit/Tensile Strength versus Tensile StrengthFigure 2.16 Ratio of endurance limit to tensile strength for various metals,as a function of tensile strength.Because aluminum does not have an endurance limit,the correlation for aluminum are based on a specific number of cycles,as is seen in Fig.2.15.2021/9/2336潛變：潛變：機械零件在長時間承受一靜態負荷時所進行的永久變形，原因為晶界滑移（grain-boundary sliding）。例如：熱塑性塑膠及橡膠會在任何溫度下進行潛變。鉛會在室溫定力下潛變、老房子的玻璃。鋁合金（200度C）、高熔點金屬（1500度C）應力釋放（應力釋放（stress relaxation）：）：螺栓、卯釘、guy wires2.8 潛變（Creep）2021/9/23372.8 潛變（Creep）潛變曲線：分三階段2021/9/23382.9 衝擊（Impact）Impact Test SpecimensFigure 2.18 Impact test specimens:(a)Charpy;簡支樑簡支樑(b)Izod.懸臂樑懸臂樑2021/9/2339Ch 2.10 材料在製造過程及使用中的破壞與斷裂破裂破裂面走向破裂vFigure 2.19、2.202021/9/2340Ch 2.10 材料在製造過程及使用中的破壞與斷裂2021/9/2341Ch 2.10 材料在製造過程及使用中的破壞與斷裂2021/9/2342圖2.21 2.222.10.1延性破壞（Ductile fracture)2021/9/23432.10.1延性破壞（Ductile fracture)杯錐狀斷裂（Cup-and-cone fracture）：空孔累積、生長合併。2021/9/23442.10.1延性破壞（Ductile fracture)雜質的影響2021/9/2345轉換溫度（轉換溫度（Transition Temperature）Figure 2.24 Schematic illustration of transition temperature in metals.transition temperature 通常比室溫低許多，材料在低溫易發生破壞通常比室溫低許多，材料在低溫易發生破壞(TITANIC!)2021/9/2346圖2.262.10.2 脆性破壞（Brittle fracture）2021/9/23472.10.2 脆性破壞（Brittle fracture）疲勞破壞疲勞破壞 海灘標記（beach marks）2021/9/23482.10.2 脆性破壞（Brittle fracture）疲勞破壞疲勞破壞改善：l1.珠擊、滾桶磨光。l2.表面硬化。l3.降低表面溝槽、缺陷提高精度。l4.選擇適當材料，降低雜質、空孔及不純物。2021/9/2349疲勞破壞疲勞破壞2021/9/23502.11 殘留應力（Residual Stresses）2021/9/23512.11 殘留應力（Residual Stresses）殘留應力原因：殘留應力原因：加工、溫度梯度殘留拉應力降低疲勞壽命、破壞強度加工形成之殘留應力，一段時間後應力破壞（stress cracking）降低殘留應力：退火（annealing）、反向變形、室溫長時間放置（溫度上升可以縮短時間）2021/9/2352Ch 2.12 功、熱及溫度上升Ch 2.12 製程中所受的限制l溫度(須避免熱漲冷縮造成尺寸形狀失準)l應變(須避免破裂產生)workheatStored energy(530%)2021/9/2353Ch 2.12Example:P100 mm100 mmgiven:find:solution:2021/9/2354P100 mm100 mm2021/9/2355
