It has been required to determine the stress distribution in a vascular wall because it may be one of the most important factors for cardiovascular diseases. The objective of this study is to analyze it by the finite element method which has been widely used in practical engineering problems. Vascular walls mainly consist of three structural components; elastin, collagen and smooth muscle. Each component is considered to have its unique and characteristic mechanical properties. It is necessary, therefore, to determine them as the fundamental data for the finite element analysis. Mechanical properties of bulk vascular walls and of each structural component were first studied experimentally by an extraction method. It was found that smooth muscle plays almost no role in the static mechanical properties of bulk vascular walls, and that elastin has high deformability and low strength, while collagen is a stiff and strong component. Stresses of elastin and of collagen can be related to their strains by exponential functions. Stresses developed in a vascular wall under static pressure were then analyzed by the finite element method. The structure of wall was assumed to be an aggregate of three different components; the elastin component, the collagen one and the one consisting of homogeneous mixtures of elastin, collagen and smooth muscle. An incrementally linear elastic model was used for the calculation. The results obtained showed that the stress distribution in a wall is very complicated and the elements of collagen in tunica media take remarkably higher stress values than the other two elements. These high stresses in collagen elements induce rather high stresses in the adjacent structures in tunica media. It can be considered from these results that a damage in a vascular wall is more easily caused in the tunica media than in the endothelium so far as the stress distribution is concerned.
General thermal-elastic plastic constitutive equations for any anisotropic materials are discussed theoretically. First, the general anisotropic thermal-elastic constitutive equations are obtained, and a plastic potential, which is a function of stress and entropy, is assumed. Then from the concept of von Mises and from the assumption of the perfect plasticity, the general thermal-elastic-plastic constitutive equations are derived. The special case of quadratic form of the plastic potential with respect to the stress and entropy is analysed. The _??_-representation is also discussed, where the constitutive equations are expressed in terms of six or seven dimensional vectors in _??_6 or _??_7.
The constitutive equations of the cubic crystal type materials are investigated theoretically. The restrictions on the fourth and second order elastic and yield coefficients are derived from the cubic symmetricity. The stress which results from the shape distortion becomes the deviatoric stress, and therefore the deformation is independent of the pressure. The mapped constitutive equations to a six-dimensional space are obtained. The constitutive equations of the isotropic plastic materials are also discussed.
It is studied in this report how the toughness of tempered Ni-Cr steel changes after this steel had been loaded at elevated temperature for long time. The main results are as follows: (1) The behavior of transition temperature depends upon the loading method, loading temperature and loading time. The rise of transition temperature is more remarkable in the case of higher loading temperature and of longer loading time. And the dynamic loading such as rotating bending makes the transition temperature to rise higher than the static tensile loading. (2) The rise of transition temperature corresponds with the increase of the carbon and chromium contents in deposit and the extent of boundary etching. It is concluded from these results that the tempered Ni-Cr steel should be used carefully, since this steel is remarkably embrittled under the condition of dynamic loading at elevated temperatures for long time.
The filling capacity of shredded tobacco is related with its resistance to compression and its specific volume. Therefore, it is assumed that the filling capacity (FC) is constituted by three factors, that is, the elastic modulus of tobacco (E), the specific volume of leaf self of tobacco (VM) and the relative bulkiness of tobacco shreds at a loose fill (VP). For the purpose of representing relationships among those four variables, quantitatively, the following multiple regression formula was statistically calculated with many experimental data obtained on typical varieties of natural tobacco cultivated in Japan. (FC)=C1+C2+C3VP+C4VM The results obtained are as follows: (1) The influence of E on FC was greater than that of VP or VM, VP and VM had similar influence on FC. (2) The esimated precision of other regression formula using VQ (the relative bulkiness of shreds at an initial moment of pressure generation) in place of VP was better than that of the above-mentioned fomula using VP. (3) Similar consequences as (1) and (2) were achieved from other calculation using EG (the elasticity per unit dry weight), VA (the total bulkiness at a loose fill of shreds, VA=VP+VM), VB (the total bulkiness at an initial moment of pressure generation VB=VQ+VM) in place of E, VP, VQ and VM. (4) In conclusion, it was confirmed that the investigation of E is indispensable to analyze FC.
Machining ability in electric discharge machining is judged by means of four factors, “machining speed”, “electrode wear ratio”, “surface roughness of worked pieces”and“isotropism of working clearance”. Since it is generally believed that the machining ability depends largely on the properties of graphite materials used as the tool-electrodes, it is obviously useful for the development of the most suitable graphite materials to make clear the relationship between the properties of graphite electrodes and the factor influencing machining ability. This report describes some of the test results examined on a series of graphite materials of various physical characteristics as well as of various grain constitution (both in shape and size) in relation to the effects of their properties on those judging factors. Experiments were carried out on an electric discharge machine currently in use, with graphite as an anodic tool-electrode under the common discharge conditions that have been proven to be optimum for graphite electrodes. The results obtained are: (1) “Machining speed”increases apparently with lowering electric resistivity of graphite electrodes as being generally considered, but since the resistivity is influenced decisively by the grain size distribution of raw materials, “machining speed”would rather be regarded to depend on the grain size. (2) “Electrode wear ratio”and“surface roughness”are, in contrast to the general belief, independent of any of the physical properties of the electrodes but depend significantly on the grain size distribution. (3) It should be pointed out that the above mentioned two factors tend to change sigmoidally in the range of mean grain size of 5 to 10μm. (4) “Anisotropy ratio”of working clearance decreases with decreasing anisotropy ratio of graphite materials being represented by the ratio of CTE's (coefficient of thermal expansion) measured in different directions of“across grain”and“with grain”.