Showing papers in "Journal of Engineering Materials and Technology-transactions of The Asme in 1989"

Conduction in Non-Crystalline Materials

Abstract: Abstract If the distance between atoms in a crystalline lattice is increased, an energy gap appears, which in a divalent material will separate occupied from unoccupied states of an electron. In a non-crystalline substance, a minimum is expected in the density of states (a ‘pseudogap’). An approximate theoretical estimate is given of the depth of the minimum at which the one-electron states become localized so that 〈σE(0)〉 vanishes; this turns out to be such that N(E F)/N(E F)free is about ⅓. The result depends rather sensitively on the parameters used; the value deduced from the experiments of Hensel and Franck (1966, 1968) on the resistivity of mercury at high temperatures gives for this ratio a value of ⅕. It is shown also that the localized states at the extremities of a valence or conduction band are of negligible importance if the wave functions are s-like on the atoms or ions, but may be of importance if they are not. A discussion is given of the electrical behaviour of chalcogenide glasses, amorph...

A Model for Abrasive-Waterjet (AWJ) Machining

Abstract: Ultrahigh-pressure abrasive-waterjets (AWJs) are being developed as net shape and near-net-shape machining tools for hard-to-machine materials. These tools offer significant advantages over existing techniques, including technical, economical, environmental, and safety concerns. Predicting the cutting results, however, is a difficult task and a major effort in this development process. This paper presents a model for predicting the depth of cut of abrasive-waterjets in different metals. This new model is based on an improved model of erosion by solid particle impact, which is also presented. The erosion model accounts for the physical and geometrical characteristics of the eroding particle and results in a velocity exponent of 2.5, which is in agreement with erosion data in the literature. The erosion model is used with a kinematic jet-solid penetration model to yield expressions for depths of cut according to different modes of erosion along the cutting kerf. This kinematic model was developed previously through visualization of the cutting process. The depth of cut consists of two parts: one due to a cutting wear mode at shallow angles of impact, and the other due to a deformation wear mode at large angles of impact. The predictions of the AWJ cutting model are checked against a large database of cutting results for a wide range of parameters and metal types. Materials are characterized by two properties: the dynamic flow stress, and the threshold particle velocity. The dynamic flow stress used in the erosion model was found to correlate with a typical modulus of elasticity for metals. The threshold particle velocity was determined by best fitting the model to the experimental results. Model predictions agree well with experimental results, with correlation coefficients of over 0.9 for many of the metals considered in this study.

Constitutive Modeling of Ratchetting Effects—Part I: Experimental Facts and Properties of the Classical Models

Abstract: Etude des effets de rochetage, soit l'accumulation progressive de deformation, cycle apres cycle, induite par une charge cyclique secondaire superposee a une charge primaire constante. Discussion de faits experimentaux et de l'exactitude des equations constitutives classiques

Pressure Effects in Abrasive-Waterjet (AWJ) Machining

Abstract: Abrasive-waterjets (AWJs) are formed by mixing high-pressure (up to 400 MPa) waterjets (0.1 to 1 mm in diameter) with abrasive particles in mixing tubes with typical 1/d ratios of 50 to 100. The pressure of the waterjet influences the overall performance of the abrasive-waterjet cutting system through operational and phenomenological effects. Higher pressures result in lower hydraulic efficiency, more frequent maintenance, high wear rates of mixing tubes, and fragmentation of particles before they exit the nozzle. However, with high pressures, deeper cuts can be obtained and higher traverse speeds can be used. Consequently, the hydraulic power is best utilized at an optimum pressure, which is a function of all other parameters as well as the application criteria. This paper presents data and analyses on the effect of pressure on nozzle operational characteristics, i.e., jet spreading characteristics, abrasive particle fragmentation, suction capability, wear of mixing tubes, and mixing efficiency. The effect of pressure on the parameters of cutting performance is discussed with example data. These parameters are depth of cut, specific area generation, maximum cutting traverse rate, surface waviness, and cost of cutting. Optimal pressure examples presented in this study indicate that pressures over 240 MPa are required for efficient abrasive-waterjet performance in metal cutting.

Constitutive Modeling of Ratchetting Effects—Part II: Possibilities of Some Additional Kinematic Rules

Abstract: Etude detaillee des possibilites de modelisation des lois de durcissement non lineaire ou lineaire dans le cadre de la plasticite independante du temps pour le cas particulier de la traction-compression. La difficulte majeure est de reduire l'effet rochetage sans perturber l'ecoulement plastique en traction. Le modele propose par Rousselier offre le meilleur compromis. Tenir compte de l'effet de memoire de la deformation permet de decrire des faits experimentaux sur l'acier inoxydable 316

Extensive Theory of Force-Approach Relations of Elastic Spheres in Compression and in Impact

Abstract: The prevailing Hertz theory in contact and in impact is based on the total compressive displacement of a semi-infinite elastic body. This paper considers displacements of finite elastic medium in each of elastic spheres and presents analytically extensive force-approach relations of the Hertz theory for two elastic spheres in statical compression and in impact. In the statical conditions, expansive displacements of the mutual surf ace of contact due to compressive displacements by the reactions, which act on the opposite surfaces in a distance equal to each diameter, are considered analytically in two approximate cases. The force-approach relations obtained here are much closer than the Hertz’s one in a wide range of deformations to one experimental result carried out for one rubber sphere. In impact, it is considered that relative position of each center of mass of the impacting spheres accompanying asymmetrical deformations is shifted from the initial position. The force-approach relation has another extensive term different from the Hertz’s relation and from the above relations in the statical conditions. In the case of very small deformations for hard spheres, the extensive terms can be neglected and the Hertz theory is valid in compression and in impact. The present force-approach relations can be applicable to the cases of large deformations in compression and in impact.

Constitutive Modeling of Anisothermal Cyclic Plasticity of 304 Stainless Steel

Abstract: Temperature-history dependence in anisothermal cyclic plasticity of 304 stainless steel is studied for the constitutive modeling within the temperature range from room temperature to 600°C Cyclic plastic behavior under in-phase and out-of-phase changes of temperature and athermal strain is analyzed first by use of an elaborate constitutive model with its material constants determined from isothermal experiments; good agreement is obtained between the predictions and experiments, if we assume that the internal change proper to higher temperature prevails under such thermomechanical cycling This finding leads us to extend the evolution equation of isotropic hardening so that it can be valid for more complex variations of temperature The extended model simulates well the recent experiments of Niitsu and Ikegami under multi-step changes of temperature

High temperature inelastic deformation under uniaxial loading - Theory and experiment

Abstract: The elevated-temperature uniaxial inelastic deformation behavior of an Ni-base alloy, B1900 + Hf, is investigated by performing isothermal tensile, creep, cyclic, stress relaxation, and thermomechanical fatigue tests. The range of strain rates examined is from 10 to the -7th to 100 per sec, while the test temperatures range from 25 to 1093 C. This extensive constitutive data base has been used for evaluating the unified constitutive models of Bodner and Partom (1972) and of Walker (1972) which apply for the small-strain regime. Comparison of test results with independent model predictions indicates good agreement over a broad range of loading conditions, demonstrating the applicability of the unified-constitutive-equation approach for describing the strongly nonlinear and temperature-dependent response of meals under a wide range of deformation and thermal histories. Thus the results give confidence that the unified approach is an effective and efficient approach in which complex history-dependent thermoviscoplastic flow can be represented within a single inelastic strain-rate term.

Growth of Short Fatigue Cracks at Notches in Woven Fiber Glass Reinforced Polymeric Composites

Abstract: The fatigue crack initiation and growth characteristics of short cracks emanating from blunt notches with root radius varying from 1.6 to 6.35 mm at various depths in women fiber-glass reinforced polymeric composites have been investigated. It is demonstrated that the initiation and growth rate of short cracks emanating from blunt notches can be accurately described by an effective stress intensity factor range ΔK eff . The ply orientations studied, did not have any effect on the analysis. The results provide an adequate engineering approach for designing against failure from range of stress concentrations, at least for this composite system