The influence of the distribution of voids on macroscopic mechanical properties is an important problem in plastic deformation of damaged materials. Since the distribution of voids in actual damaged materials is heterogeneous, we have to evaluate the heterogeneous distribution of voids quantitatively. We propose a new method using the voronoi tessellation and the stereology to evaluate the heterogeneous distribution of voids in this paper. In order to verify the availability of the new method, perforated sheets with randomly distributed holes are set up as plane models of damaged materials and are examined under uniaxial tension. Mechanical properties of perforated sheets are estimated by anisotropic yield function and the relationship between distiribution of holes and macroscopic yield stress is investigated quantitatively. It is shown that the method is valid for evaluating the heterogeneous distribution of holes.
Shrink fit has been used commonly for joining the cylindrical components such as shaft and gears. It is noted recently the shrink fitted joint with anaerobic adhesives is adopted in order to improve it's joint strength. In a reliable design of bonded shrink fitted joints, it is necessary to know the contact stress distributions at the interfaces. In this paper, the interface stress distribution of bonded shrink fitted joint under push-off force is analyzed by using axisymmetric theory of elasticity as four-body contact problem. Analogical test is conducted to determine the relationship between the normal stress and the shear stress. Using the interface stress distribution and analogical test results, a method for estimating the joint strength is proposed. In the numerical calculations, the effect of the outer diameter and Young's modulus of the rings and the engagement length on the contact stress distributions at the interfaces are clarified. Push-off force measurement was carried out for bonded shrink fitted joints. In the experiments, the effect of shrink fit interference and the outer diameter of ring on the joint strength are examined. The numerical results are in a fairly good agreement with the experimental results. It is found that the strength of the bonded shrink fitted joint is greater than that of shrink fitted joint.
This paper presents a new scheme for the second-order shape design sensitivity analysis of the two-dimensional elastic problem by the element-free Trefftz method. In the Trefftz formulation, the physical quantities are approximated by the superposition of the regular T-complete functions. Therefore, direct differentiation of the approximate expressions with respect to shape parameters leads to the regular expressions of the sensitivities. The present schemes are applied to simple examples in order to confirm the validity.
One of the main problems of the Wavelet-Galerkin Method is the treatment of boundary conditions. To deal with this difficulty, the boundaries of wavelet series expansion are assumed to be the analytic boundaries of the problem. The boundary condition equations are replaced by end equations in the Galerkin system. The manipulation discussed here enables us to use classical wavelets and to tackle the problem more simply. However, we find that the end equations are a necessary part of the Galerkin equation system within the boundaries. To maintain the integrity of the system, the boundaries of wavelet series expansion are shifted until the end equations do not depend on any expansion coefficients ck of φ(2jx-k)that affect the solution within the real boundaries. Therefore replacing the end equations gives a good result in comparison to the exact solution.
An effective laminate design method is shown for thermoelastic properties of symmetric laminates with extension-shear or bending-twisting coupling. The relationship between thermoelastic properties and laminate configurations is examined by using lamination parameters which can express any laminate configuration. The coefficient of thermal expansion(CTE) is represented on the lamination parameter plane. The graphical representation clarifies the effect of laminate configurations on the CTE. It is shown that the CTE of graphite/epoxy composites can be controlled in a wide range from positive to negative values by tailoring laminate configurations. Thermal deformation characteristics of symmetrically laminated plates are also examined using lamination parameters for simply supported plates under two temperature conditions. An optimal laminate design of symmetrically laminated plates for thermal deformation is shown based on a mathematical programming method where four lamination parameters are used as design variables.
A strip element method is presented to determine bending solutions of orthotropic plates. In this method, the plate is discretized into strip elements in one direction. By using the principle of minimum potential energy to a strip element, a set of fourth-order ordinary differential equations with respect to the other direction are derived. By assembling the corresponding equations of adjacent strip elements, differential equations for the whole plate are obtained. These equations can be solved analytically by using the Fourier transform method. The deflection distribution is determined by using the boundary conditions. Numerical examples for an orthotropic plate are presented and it is shown that the strip element method is an efficient and accurate numerical method for the plate bending analysis.
The caustics experimental method is effective for the analysis of stress concentration or stress singularity. We have studied the basic characteristics of caustics under conditions of distributed loads. Thus, we have discussed many characteristics of caustics under various load conditions and different reflective planes using differently shaped specimens. In this paper, the application of the caustics experimental method to conditions of distributed loads is emphasized. Considering a real cutting system, the reflective planes are set on front and rear surfaces. An inverse problem, i.e., a method to estimate the external force or corresponding stress distribution from the experimental caustic curve is discussed.
An infrared radiation(IR) heating method was used to evaluate thermal shock parameters(thermal shock strength and thermal shock fracture toughness)of float glass and alumina. This technique makes it possible to evaluate the parameters directly from the electric power of the IR heater. In this paper we discuss how the pertinent thermal shock parameters should be estimated both as physical properties of a material and as a function of temperature. The stress intensity factors for a disk with an edge crack were analyzed numerically under a thermal shock loading. The thermal shock parameters in both ambient and elevated-temperature environments were measured by the IR heating technique and the results were compared with predicted values, which combined such emperature-dependent properties of the material as Young's modulus, thermal conductivity, linear thermal expansion, and tensile strength or fracture toughness.
Delamination crack growth behavior under mode II cyclic loading was investigated with interlayer-toughened CFRP laminate, T800H/3900-2. Fatigue tests under a constant maximum energy release rate showed that the growth rate was independent of the crack length. Then, load-shedding tests were carried out under various stress ratios. The fatigue crack growth resistance of the interlayer-toughened CFRP was higher than that of conventional CF/epoxy. The crack growth rate under various stress ratios was well correlated to the stress intensity range near the threshold region. Thus, the mechanism of fatigue fracture under mode II loading is completely different from that under mode I loading. Fractographic observation showed that the fatigue fracture occurred on the principal shear stress plane. Large hackle patterns which are typical for static mode II tests were not observed under fatigue loading. A mesoscopic fracture model was proposed to explain the microscopic observation and the stress ratio dependence.
In order to elucidate the mechanism of deformation and fracture of microcomponents, numerical simulations are conducted for a nanoscopic wire and film of nickel without lattice defects on the basis of a molecular dynamics using the EAM(embedded atom method) potential. A bulk of nickel is also treated by applying a periodic boundary condition for comparison. These materials are subjected to a tensile strain along thedirection of the fcc(face-centered cubic) lattice. Here, the transverse stresses in the bulk material are kept at zero during tension. The yielding is brought about by the crystallographic slips on the(111)planes and there is little difference in the yield stress among the wire, film and bulk. The slips continue to take place on multiple(111)planes and the plastic deformation leads to ductile fracture. Next, the displacement in the transverse direction on the cell boundaries of the bulk is fixed in order to investigate the effect of constraint. It shows brittle fracture due to cleavage cracking. This implies that the constraint, which may be introduced by local inhomogeneity of the material, brings about early crack nucleation and reduces the ductility of materials without lattice imperfection.
Chromium nitride(CrN) exhibits good corrosion resistance in addition to excellent electrical and mechanical properties. A decrease in the number of defects such as pinholes or voids formed during deposition is required for improvement of corrosion resistance and corrosion fatigue strength of coated materials. A multistage physical vapor deposition(PVD) method was proposed in order to fabricate dense thin-coating films. In an electrochemical anodic polarization test in aerated 2%H2SO4 solution, 0.37 wt%C steel that was coated with CrN thin film using the multistage PVD method showed better corrosion resistance than a specimen coated by a conventional method. This is due to a decrease in the number of small defects in the coating film deposited using the multistage PVD method. Evaluation of the corrosion fatigue strength of multistage-coated steel was performed by means of a cantilever-type rotating-bending fatigue test in 3%NaCl solution. The corrosion fatigue strength of multistage-coated steel was improved compared with that of the uncoated steel;however, the increase in fatigue strength was less in the multistage-coated specimen than in the specimen coated by the conventional method, contrary to the experimental results obtained from the anodic polarization test. It was pointed out that corrosion fatigue strength is dependent on not only the number of defects but also the shape of large defects in the coating film.
Fatigue crack propagation behavior was investigated using structural carbon steel specimens which have single edge or small surface pre-cracks. The crack closure behavior of small surface cracks was dynamically measured by using an interferometric displacement gage with a laser diode. The threshold condition for crack initiation from pre-cracks was given by the effective stress intensity range obtained for long cracks. The crack opening stress intensity factor increased with crack growth. The threshold crack opening stress intensity factor was formulated as a function of the ratio of the applied stress to the yield stress and the increment of crack length. The cyclic R-curve was constructed in terms of the experimentally determined threshold value of the maximum stress intensity factor which was the sum of the range of the threshold effective stress intensity and the crack opening stress intensity factor. The cyclic R-curve method was used to predict the fatigue thresholds of the pre-cracked components. The predicted values of the fatigue limit for crack initiation, the fatigue limit for fracture, and the length of non-propagating cracks agreed well with the experimental results
Direct bonding between aluminum and silicon was successfully achieved due to the formation of hydrogen bonds at the interface. The substrates were treated so that their surfaces were hydrophilic, then OH groups and water molecules were adsorbed onto their surfaces. Two hydrophilic treatments, a wet process and a dry process, were used. In the dry process, the adsorption of OH groups was achieved by bombardment with hydro-ions produced by passing steam through an ion source. The bonding efficiency of samples treated using the dry process was better than that of samples treated using the wet process and ranged from 30 to 90% when the heat treatment time was longer than 2 hours. Secondary ion mass spectrometry(SIMS) indicated the presence of oxygen and hydrogen adjacent to the bonding interface, and the formation of hydrogen bonds between them was confirmed using Fourier transform infrared reflection absorption spectroscopy(FTIR-RAS).
Under the assumption of an elastic roller, and ignoring the heat transfer problem, in this study we determined explored the distribution of elastic deformation of the roller when the roller contacted with the strip in the rolling area during the rolling process. In addition, in this study, based on the large deformation-large strain theory, the updated Lgrangian formulation(ULF) and the incremental principle were used to develop 3D elastic plastic analytical model of aluminum strip rolling. The flow stress was considered to be a function of strain and strain rate. We also studied the effect of a slightly convex shape of the axial cross section surface of the roller on the flatness of the strip surface. For the main purpose of this study, we used a proposed iteration process to calculate on the elastic contact deformation and the contact face of the roller, when the roller contacted with the strip. An error value was also designated to compare the displacement increments of the strip using two iterations to detemine whether the iteration was terminated. In this study, the extent of elastic deformation of rollers with flat surfaces in the rolling region was used to compensate for the roller radius to produce a slightly convex shape on the roller surface. This reduces the effect of roller deformation on strip shapes. Changes in strip shape were also analyzed.