【正文】 中流動最儔的地方,隨著壓力機(jī)滑塊繼續(xù)下行,，在拉深的工序中，這部分很少發(fā)生變形。四 凸模、凹模的圓角半徑應(yīng)為46倍料厚以防止裂紋及起皺。毛坯變形情況為周向壓縮么向拉伸，這樣被拉入凹模圓腔中的工序稱為拉深，拉深過程有：摩擦壓縮、拉伸?？朔蓧哼吶澾^凹模圓角在后面行程中校直成直壁材料的變形力。而且沿著圓周半徑方向上壓縮量隨著半徑增大而增大——半徑越大的地方，需壓縮的面積也大，這樣的結(jié)果是壓邊圈部分的材料變厚，而凸模部分的材料因?yàn)楸焕钭儽?。最薄的區(qū)域是沖壓件直壁與圓角過渡部分，因?yàn)檫@部分在拉深過程中拉伸變形最久，受力最大，這里往往也是最容易拉裂的地方，因?yàn)檫@部分的加工硬化少于其它地方。沖壓件離開凸模產(chǎn)生的真空部分如果不設(shè)通氣孔，沖壓件將很難脫出。 the Young’s modulus (E), the Poisson’s ratio (S), and the initial yield stress (y). For a rigidplastic material, only the yield stress is required. These data must be obtained from experiments or a material handbook. These values may vary with temperature in a coupled analysis. This is prescribed using the TABLES option. The flow stress of the material changes with deformation, so called strain hardening or workhardening behavior and may be influenced by the rate of deformation. These behavior are also entered via the TABLES option.The linear elastic model is the model most monly used to represent engineering materials. This model, which has a linear relationship between stresses and strains, is represented by Hooke’s Law. Figure D1 shows that stress is proportional to strain in a uniaxial tension test. The ratio of stress to strain is the familiar definition of modulus of elasticity (Young’s modulus) of the material.E (modulus of elasticity) = (axial stress)/(axial strain) （）Experiments show that axial elongation is always acpanied by lateral contraction of the bar. The ratio for a linear elastic material is:v = (lateral contraction)/(axial elongation) ()This is known as Poisson’s ratio. Similarly, the shear modulus (modulus of rigidity) is defined as:G (shear modulus) = (shear stress)/(shear strain) ()It can be shown that for an isotropic materialG = E / 2 (1+n) () The stressstrain relationship for an isotropic linear elastic method is expressed as： Where is the Lame constant and G (the shear modulus) is expressed as： The material behavior can be pletely defined by the two materialconstants E and n.TimeIndependent Inelastic BehaviorIn uniaxial tension tests of most metals (and many other materials), the following phenomena can be observed. If the stress in the specimen is below the yield stress of the material, the material will behave elastically and the stress in the specimen will be proportional to the strain. If the stress in the specimen is greater than the yield stress, the material will no longer exhibit elastic behavior, and the stressstrain relationship will bee nonlinear. Figure D2 shows a typical uniaxial stressstrain curve. Both the elastic and inelastic regions are indicated.Within the elastic region, the stressstrain relationship is unique. Therefore, if the stress in the specimen is increased (loading) from zero (point 0) to s1 (point 1), and then decreased (unloading) to zero, the strain in the specimen is also increased from zero to e1, and then returned to zero. The elastic strain is pletely recovered upon the release of stress in the specimen. Figure D3 illustrates this relationship. The loadingunloading situation in the inelastic region is different from the elastic behavior. If the specimen is loaded beyond yield to point 2, where the stress in the specimen is s2 and the total strain is e2, upon release of the stress in the specimen the elastic strain, is pletely recovered. However, the inelastic (plastic) strain remains in the specimen. Figure D3 illustrates this relationship. Similarly, if the specimen is loaded to point 3 and then unloaded to zero stress state, the plastic strain remains in the specimen. It is obvious that is not equal to. We can conclude that in the inelastic region? Plastic strain permanently remains in the specimen upon removal of stress.? The amount of plastic strain remaining in the specimen is dependent upon the stress level at which the unloading starts (pathdependent behavior).The uniaxial stressstrain curve is usually plotted for total quantities (total stress versus total strain). The total stressstrain curve shown in Figure D2 can be replotted as a total stress versus plastic strain curve, as shown in Figure D4. The slope of the total stress versus plastic strain curve is defined as the workhardening slope (H) of the material. The workhardening slope is a function of plastic strain.The stressstrain curve shown in Figure D2 is directly plotted from experimental data. It can be simplified for the purpose of numerical modeling. A few simplifications are shown in Figure D5 and are listed below:1. Bilinear representation – constant workhardening slope2. Elastic perfectlyplastic material – no workhardening3. Perfectlyplastic material – no workhardening and no elastic response4. Piecewise linear representation – multiple constant workhardening slopes5. Strainsoftening material – negative workhardening slopeIn addition to elastic material constants (Young’s modulus and Poisson’s ratio), it is essential to be concerned with yield stress and workhardening slopes in dealing with inelastic (plastic) material behavior. These quantities vary with parameters such as temperature and strain rate, further plicating the analysis. Since the yield stress is generally measured from uniaxial tests, and the stresses in real structures are usually multiaxial, the yield condition of a multiaxial stress state must be considered. The conditions of subsequent yield (workhard