【正文】 一個(gè)轂或者孔的內(nèi)徑比與它相配的軸或者圓柱的直徑小一點(diǎn)。減少的壓力集中影響的方法通常就是使在形狀上的變化更有規(guī)律性。從圖表里的時(shí)間軸上 (x 軸 )，我們可以描述在 10 年的時(shí)間里，這種產(chǎn)品的預(yù)期壽命。因此，如果一個(gè)零件是在很強(qiáng)的強(qiáng)度下運(yùn)轉(zhuǎn)的話，那么設(shè)計(jì)工程師必須精確地預(yù)言將在機(jī)器的使用壽命期間可能發(fā)生的蠕變的次數(shù)。 當(dāng)溫度升高時(shí)，圖 顯示了低碳鋼在彈性模數(shù) E 方面的削減。而疲勞曲線的繼續(xù)變小，表明不管作用力有多么的小，多次的應(yīng)力反復(fù)作用都會(huì)引起零件的失效。對于鋼的材料來說，持久極限值大約等于極限強(qiáng)度的 50%。然后根據(jù)壓力值和所需的循環(huán)的次數(shù)來繪制一個(gè)圖。 一種材料的疲勞強(qiáng)度是指在壓力的反復(fù)作用下的抵抗產(chǎn)生裂縫的能力。對斷面的檢查可以發(fā)現(xiàn)一種非常有趣的圖案，如圖 中所示。一個(gè)例子就是一臺升降機(jī)墜落到位于通道底部的一套彈簧裝置上，這套裝置產(chǎn)生的力會(huì)比升降機(jī)本身的重量大上好幾 倍。此外，我們通常也把很少發(fā)生變化的作用力叫作靜載荷。因此，一種可延展的材料通常是由于變形受壓而損壞的，并不是壓力的原因。一般說來，材料越硬，它的脆性也越大，因此，彈性越小。顯而易見，脆性材料的韌性和彈性非常低，并且大約相等。因此靜強(qiáng)度可以被認(rèn)為是大約等于比例極限，從理論上來說，我們可以認(rèn)為在這種情況下，材料沒有發(fā)生塑性變形和物理破壞。 凸輪是被應(yīng)用的最廣泛的機(jī)械結(jié)構(gòu)之一 ， 是一種僅僅有兩個(gè) 組件構(gòu)成的設(shè)備。發(fā)生了過度的變形，但并沒有產(chǎn)生裂縫，也可能會(huì)引起一臺機(jī)器出毛病，因?yàn)榘l(fā)生畸變的零件會(huì)干擾下一個(gè)零件的移動(dòng)。后者發(fā)生的這次故障造成的結(jié)果通常只不過是一些暖氣裝置里冷卻劑的損失，是一種很容易被發(fā)現(xiàn)并且被改正的情況。 Failure Analysis， Dimensional Determination And Analysis，Applications Of Cams Jack Bauble Abstract： It is absolutely essential that a design engineer know how and why parts fail so that reliable machines that require minimum maintenance can be designed； Cams are among the most versatile mechanisms available． A cam is a simple twomember device． The input member is the cam itself， while the output member is called the follower． Through the use of cams， a simple input motion can be modified into almost any conceivable output motion that is desired． Key words: failure highspeed cams design properties INTRODUCTION It is absolutely essential that a design engineer know how and why parts fail so that reliable machines that require minimum maintenance can be designed． Sometimes a failure can be serious， such as when a tire blows out on an automobile traveling at high speed． On the other hand， a failure may be no more than a nuisance． An example is the loosening of the radiator hose in an automobile cooling system． The consequence of this latter failure is usually the loss of some radiator coolant， a condition that is readily detected and corrected． The type of load a part absorbs is just as significant as the magnitude． Generally speaking， dynamic loads with direction reversals cause greater difficulty than static loads， and therefore， fatigue strength must be considered． Another concern is whether the material is ductile or brittle． For example， brittle materials are considered to be unacceptable where fatigue is involved． Many people mistakingly interpret the word failure to mean the actual breakage of a part． However， a design engineer must consider a broader understanding of what appreciable deformation occurs． A ductile material， however will deform a large amount prior to rupture． Excessive deformation， without fracture， may cause a machine to fail because the deformed part interferes with a moving second part． Therefore， a part fails(even if it has not physically broken)whenever it no longer fulfills its required function． Sometimes failure may be due to abnormal friction or vibration between two mating parts． Failure also may be due to a phenomenon called creep， which is the plastic flow of a material under load at elevated temperatures． In addition， the actual shape of a part may be responsible for failure． For example， stress concentrations due to sudden changes in contour must be taken into account． Evaluation of stress considerations is especially important when there are dynamic loads with direction reversals and the material is not very ductile． In general， the design engineer must consider all possible modes of failure， which include the following． —— Stress —— Deformation —— Wear —— Corrosion —— Vibration —— Environmental damage —— Loosening of fastening devices The part sizes and shapes selected also must take into account many dimensional factors that produce external load effects， such as geometric discontinuities， residual stresses due to forming of desired contours， and the application of interference fit joints． Cams are among the most versatile mechanisms available． A cam is a simple twomember device． The input member is the cam itself， while the output member is called the follower． Through the use of cams， a simple input motion can be modified into almost any conceivable output motion that is desired． Some of the mon applications of cams are —— Camshaft and distributor shaft of automotive engine —— Production machine tools —— Automatic record players —— Printing machines —— Automatic washing machines —— Automatic dishwashers The contour of highspeed cams (cam speed in excess of 1000 rpm) must be determined mathematically． However， the vast majority of cams operate at low speeds(less than 500 rpm) or mediumspeed cams can be determined graphically using a largescale layout． In general，the greater the cam speed and output load， the greater must be the precision with which the cam contour is machined． DESIGN PROPERTIES OF MATERIALS The following design properties of materials are defined as they relate to the tensile test． Static Strength． The strength of a part is the maximum stress that the part can sustain without