Normal Stress Effects Research Articles

Effect of normal stresses on the results of thermoplastic mold filling simulation

The paper deals with the effect of the normal stresses on the predicted flow front during the filling stage of thermoplastic injection molding. The normal stresses are predicted using the non-linear Criminale-Ericksen-Filbey model (a variant of the second-order fluid rheological model with viscosity, first and second normal stress coefficients dependent upon magnitude of shear rate) incorporated into a comprehensive 3D simulation software for mold-filling analysis. The additional stress term allows the prediction of the so called ear-flow effect (melt racing on the edges of the cavity).

Effects of normal stress, surface roughness, and initial grain size on the microstructure of copper subjected to platen friction sliding deformation

The effects of applied normal stress, surface roughness, and initial grain size on the microstructure of pure Cu developed during platen friction sliding deformation (PFSD) processing were investigated. In each case, the deformation microstructure was characterized and the hardness of the treated surface layer was measured to evaluate its strength. The results indicated that the thickness of the deformed layer and the hardness at any depth increased with increasing normal stress. A smaller steel platen surface roughness resulted in less microstructural refinement, whereas the microstructural refinement was enhanced by decreasing the surface roughness of the Cu sample. In the case of a very large initial grain size (d > 10 mm), a sharper transition from fine-grain microstructure to undeformed material was obtained in the treated surface layer after PFSD processing.

Development of Micro-shear Fatigue Test and its Application to Single Crystal of Pure Iron

In this study, a new fatigue testing method under shear and axial loading was developed for small specimens (3mm long and 0.3mm thick). The method was applied to a single crystal of pure iron and extra-low carbon steel in order to investigate the effect of shear and normal stress on cyclic slip activity. The specimen was sufficiently small to be prepared from a single crystal, aiming at a specific slip system in the shear loading direction. Moreover, the specimen had a single edge notch, which was designed to generate both pure shear stress and normal stress. Using this testing method, shear fatigue strength with a static normal stress on the slip system ▪[111] was evaluated, and the fatigue strength was compared with that of polycrystalline ferrite steel with static axial loading.

An Improved Short-Beam Method for Measuring Multiple Constitutive Properties for Composites

Abstract The short beam shear (SBS) test method combined with digital image correlation (DIC) deformation measurement is used in this work to study constitutive properties of the IM7/8552 carbon/epoxy composite material system. Dependence of the shear stress approximation on the SBS specimen span-to-thickness (s/t) ratio has been investigated. A stress model developed in a previous study is expanded to account for this dependency. In addition, the effect of nonzero transverse normal stresses on a simple closed-form approximation for tensile and compressive axial moduli has been assessed. Results from the expanded closed-form solution verify that transverse normal stress has little influence on the measurement of the axial moduli. Also, the SBS test setup has been refined as a result of the sensitivity of the measured axial strain distribution to the specimen alignment in the test fixture. The test results obtained in this work are compared with previously published results to demonstrate the ability of a single unidirectional SBS test to capture multiple constitutive properties including axial tensile and compressive moduli, the nonlinear shear stress–strain response in the plane of loading, and to show that measured material properties do not depend on the test specimen size.

Diagnosis of Osteoporosis and Radiotherapy Induced Fracture by F-18 FDG PET/CT in A Case with Colon Cancer

Pelvic Insufficiency Fractures (PIF) is caused by the effect of normal or physiologic stresses on bone with reduced mineral content or elastic resistance. Positron Emission Tomography (PET)/Computed Tomography (CT) is widely used in the work-up of patients with various types of cancer. In our case, a patient with colon cancer who was investigated by many forms of conventional imaging for pelvic pain. We found to have osteoporotic fractures using PET/CT.

Mgの変形機構における垂直応力の影響に関する原子論的解析

Mgの変形機構における垂直応力の影響に関する原子論的解析

THERMO-ELASTIC ANALYSIS OF FGM PLATES BASED ON HIGHER ORDER REFINED COMPUTATIONAL MODEL

In this paper, analytical formulations and solutions hitherto not reported in the literature are presented for the thermally loaded simply supported Functionally Graded Material (FGM) plates. Higher order refined computational model with twelve degrees-offreedom based on Taylor’s series of expansion of displacements, which includes the effect of transverse shear and transverse normal stress / strain is considered for the study. The equations of equilibrium are obtained using Principle of Minimum Potential Energy (PMPE) and closed form solutions using Navier’s Solution technique. The material properties are assumed to vary according to power law function. The temperature across the plate thickness is assumed to be nonlinear and is solved based on one dimensional steady state heat conduction equation. The accuracy of the presented two-dimensional model is first established by comparing the results with the exact 3-D elasticity solutions already reported in the literature. Upon establishing the accuracy, numerical results are obtained for the FGM plates subjected to thermal loads with varying material and plate parameters. Studies are performed by varying the length to breadth ratio, side-to-thickness ratio and power law parameter. Bench mark results using the present model are presented for the displacements, in-plane and transverse stresses.

Effects of normal stresses on the homogeneous nucleation of a basal dislocation in magnesium

A quantitative evaluation of the deformation of metals is usually based on the critical resolved shear stress (CRSS), in which the influence of the normal stresses is not taken into account. Although it is plausible to use the CRSS for a quantitative evaluation of the deformation mode, some previous studies show that the CRSS depends on other stress components. In this work, atomistic simulations are performed to study the influence of the normal stresses on the nucleation of basal dislocations in a magnesium single crystal. We found that the activation free energy of dislocation nucleation decreases as the normal stress applied in the [112¯0] direction decreases, or that in the [0001] direction increases. This tendency is consistent with the dependence of CRSS on the loading direction found in a previous work done by Barrett et al. (2012) on molecular dynamics simulations of tensile deformation tests of a magnesium single crystal.

Effects of normal and shear stresses in rolling and mixed mode contact on the micropitting wear of a WC/a-C:H tribological coating

The focus of this research was to evaluate the resistance of a WC/a-C:H coating to micropitting damage in rolling/sliding boundary lubricated contacts. Experiments were conducted on uncoated discs and coated rollers in a three-disc-on-roller tribometer. Contributions of surface roughness, slide-to-roll ratio, and substrate hardness on coating performance were studied. Observations gleaned from the experimental results include that the coating on a super-finished roller can withstand contact stresses as high as 1.7GPa in extreme boundary lubrication and nominally pure rolling with no measurable wear. Roughness of the coated component plays a crucial role in coating performance, as well as in the wear on the uncoated counterpart.

Interfacial sliding in a bi-layered multiferroic ceramics: Localized sliding-prevention/promotion based mechanism of intra-layer fracture

Different types of sliding regions on the interface ( a 1 = 0 mm; b 1 = 4 mm; a 2 = 31 mm; b 2 = 33 mm; d = 2 mm; β ̂ 1 = 10; f = 3). • A prevention/promotion model is proposed to formulate interfacial sliding. • Local positive normal stress gives rise to local sliding-promotion effect. • Local negative normal stress leads to local sliding-prevention effect. • Local sliding-prevention/promotion based fracture mechanisms are revealed. Sliding is a typical failure mode of composite interfaces. According to traditional theory, interfacial sliding can be represented by the linear shear-spring model (LSSM). Although the required driving interfacial shear stress has been characterized by LSSM, the relation between interfacial normal stress and sliding is not yet reflected by it. The present paper proposes an interfacial sliding-prevention/promotion model to consider the effect of interfacial normal stress on interfacial sliding. As an example of application, the intra-layer fracture problem is analyzed on a bi-layered multiferroic ceramics. Green’s functions are derived to construct the Cauchy singular integral equations, which are further numerically solved to get mechanical strain energy release rate (MSERR) and interfacial normal stress. Parametric studies yield a new finding that non-zero normal stress may be produced in local interfacial regions by intra-layer cracks under pure in-plane shear. Local positive normal stress gives rise to local sliding-promotion effect, while local negative normal stress leads to local sliding-prevention effect. The interfacial shear imperfection and local sliding-prevention/promotion constitute the mechanisms for the variation of MSERRs of the two intra-layer cracks.

Static and free vibration analysis of functionally graded plates based on a new quasi-3D and 2D shear deformation theories

In this study, two dimensional (2D) and quasi three-dimensional (quasi-3D) shear deformation theories are presented for static and free vibration analysis of single-layer functionally graded (FG) plates using a new hyperbolic shape function. The material of the plate is inhomogeneous and the material properties assumed to vary continuously in the thickness direction by three different distributions; power-law, exponential and Mori–Tanaka model, in terms of the volume fractions of the constituents. The fundamental governing equations which take into account the effects of both transverse shear and normal stresses are derived through the Hamilton's principle. The closed form solutions are obtained by using Navier technique and then fundamental frequencies are found by solving the results of eigenvalue problems. In-plane stress components have been obtained by the constitutive equations of composite plates. The transverse stress components have been obtained by integrating the three-dimensional stress equilibrium equations in the thickness direction of the plate. The accuracy of the present method is demonstrated by comparisons with the different 2D, 3D and quasi-3D solutions available in the literature.

Propulsion of axisymmetric swimmers in viscoelastic liquids by means of torsional oscillations

Unconventional methods are needed in order to propel swimming objects in viscoelastic liquids. The paper deals with a locomotion principle based on a cyclic action which utilizes the elasticity of the fluid. The theoretical model considers any incompressible simple fluid of arbitrarily long memory and any axisymmetric swimmer of arbitrary profile which performs torsional oscillations of small amplitude. Perceiving the flow as unsteady perturbation of the rest state, an asymptotic analysis is developed, particularly with regard to the time-averaged speed of the swimmer in second-order approximation. In doing so, also inertia effects are considered in addition to the memory and the normal stress effects. A generalized reciprocal theorem including fluid elasticity proves to be extremely useful. It enables calculating the driving force on the swimmer without solving the second-order flow problem. General results are illustrated by means of a spherical swimmer. The analytical findings clearly show the influence of different process parameters including certain frequency dependent constitutive parameters on the driving force, on the swimming speed and on the secondary flow field.

Density functional theory calculation of ideal strength of SiC and GaN: Effect of multi-axial stress

First-principles density functional theory calculations are performed to quantitatively evaluate the ideal strength of SiC and GaN crystals. The effect of transverse normal stress on the tensile strength and that of hydrostatic stress on the shear strength are clarified for various crystal structures: 3C, 2H and 4H for SiC, zincblende (Z) and wurtzite (W) for GaN. The effect of polytype SiC structures on the shear strength of some shear systems appears to be significant, while that on the tensile strength is marginal. While the ideal tensile strength generally decreases by transverse (perpendicular) tension, large transverse compression reduces the strength in some structures and orientations ([110] tension in 3C–SiC and Z–GaN; [21¯1¯0] tension in 2H–SiC, 4H–SiC and W–GaN) due to structural phase transition. Although SiC and GaN are basically brittle materials, our investigation suggests that not only cleavage by tension but also sliding due to shear stress take place depending on the multi-axial stress condition.

Investigation of Fault Permeability in Sands with Different Mineral Compositions (Evaluation of Gas Hydrate Reservoir)

We used a ring-shear apparatus to examine the perpendicular permeability of sands with different mineral compositions to evaluate fault behavior around gas hydrate reservoirs. The effect of effective normal stress on the permeability of two sand types was investigated under constant effective normal stresses of 0.5–8.0 MPa. Although Toyoura sand and silica sand No. 7 mainly comprise quartz, silica sand No. 7 contains small amounts of feldspar. For Toyoura sand, the permeability after ring-shearing dramatically decreased with increasing effective normal stress up to 3.0 MPa, then gradually decreased for stresses over 3.0 MPa, whereas the permeability after ring-shearing of silica sand No. 7 rapidly decreased with increasing effective normal stress up to 2.0 MPa. Although the relationships between the permeability after ring-shearing and effective normal stress for both sands could be expressed by exponential equations up to 3.0 MPa, a more gradual change in slope was shown for Toyoura sand. The permeabilities of both sands were almost equal for effective normal stresses over 3.0 MPa. The mineralogical properties of the small amount of feldspar in the sample indicate that both mineralogy and original grain size distribution affect the fault permeability and shear zone formation.

Analysis of composite steel-concrete beams using a refined high-order beam theory

A finite element model is presented for the analysis of composite steel-concrete beams based on a refined high-order theory. The employed theory satisfies all the kinematic and stress continuity conditions at the layer interfaces and considers effects of the transverse normal stress and transverse flexibility. The global displacement components, described by polynomial or combinations of polynomial and exponential expressions, are superposed on local ones chosen based on the layerwise or discrete-layer concepts. The present finite model does not need the incorporating any shear correction factor. Moreover, in the present C¹-continuous finite element model, the number of unknowns is independent of the number of layers. The proposed finite element model is validated by comparing the present results with those obtained from the three-dimensional (3D) finite element analysis. In addition to correctly predicting the distribution of all stress components of the composite steel-concrete beams, the proposed finite element model is computationally economic.

Anisotropy of tensile strength and fracture mode of perfect face-centered-cubic crystals

This study presents an effective method to calculate the ideal tensile strength of six face-centered-cubic (fcc) crystals (Cu, Au, Ni, Pt, Al, and Ir) along an arbitrary tensile direction by considering the coupling effect of normal stress and shear stress on a given crystallographic plane. Meanwhile, the fracture modes of the six crystals can also be derived from the competition between shear and cleavage fracture along different crystallographic planes. The results show that both the intrinsic factors (the ideal shear strength and cleavage strength of low-index planes) and the orientation may affect the tensile strength and fracture modes of ideal fcc crystals, which may give the reliable strength limit of fcc metals and well interpret the observed high strength in nano-scale mechanical experiments.

Experimental and theoretical study of the anisotropic properties of shale

The effect of bedding plane orientations on shear strength and failure mechanisms of shale is investigated, with an emphasis on the shear parameters of the bedding planes. This study is based on direct shear tests conducted on directional shale samples obtained from formations which exhibit well-developed stratification. The tested cylindrical specimens were prepared by coring at 30° intervals from the direction of the bedding planes. The results indicate that the anisotropy of the shear strength of shale can be readily observed due to the anisotropic effects of bedding plane orientation and normal stress. The shear parameters, such as strength, cohesion and internal friction angle reach their maximum and the minimum values at β=60° and β=0°, respectively, where β is the angle between the bedding planes and the coring orientation, which is also the direction of normal stress during the laboratory tests. It is demonstrated that the bedding planes are weak not only with regards to cementing strength, but also with regards to friction. Three different shear failure modes were built up depending on the shearing angle β: (1) sliding failure across the bedding planes, (2) sliding failure along the bedding planes and (3) sliding failure across the bedding planes combined with tensile splitting along the bedding planes. An expression of the shear stress concentration factor of the direct shear model is derived to evaluate the anisotropy of shear strength.

Adhesion force in fluids: effects of fingering, wetting, and viscous normal stresses.

Probe-tack measurements evaluate the adhesion strength of viscous fluids confined between parallel plates. This is done by recording the adhesion force that is required to lift the upper plate, while the lower plate is kept at rest. During the lifting process, it is known that the interface separating the confined fluids is deformed, causing the emergence of intricate interfacial fingering structures. Existing meticulous experiments and intensive numerical simulations indicate that fingering formation affects the lifting force, causing a decrease in intensity. In this work, we propose an analytical model that computes the lifting adhesion force by taking into account not only the effect of interfacial fingering, but also the action of wetting and viscous normal stresses. The role played by the system's spatial confinement is also considered. We show that the incorporation of all these physical ingredients is necessary to provide a better agreement between theoretical predictions and experiments.

Stress Analysis of Rotary Vibration of Rigid Friction Pile and Stress General Solution of Central Symmetry Plane Elastic Problem

The rotary vibration of rigid friction pile can be seen approximately as a central symmetry plane problem in elasticity. The stress general solution of central symmetry plane problem in elasticity can be constructed by technique such as the Laurent expansion of the volume force. This solution has some decoupling, generalized, and convergent properties, and it can be used in stress analysis of the rotary vibration of pile. The analysis results show that the maximum value of displacement will not occur at the edge of the pile and the assumption that pile cross section remains unchanged is no longer applicable, if the value of one dimensionless quantity, reflecting the angular frequency of the rotation, radius, and material properties of the pile, is larger than 1.84. Once the rotary vibration of rigid friction pile happens, the pile may lose its bearing capacity under the comprehensive effect of normal and shear stress of the pile-soil interface and it will be very difficult to recover.

Experimental Investigation of Erosion of Stainless Steel by Liquid-solid Flow Jet Impingement

Erosion of pipeline has in long time been an important issue due to the high particle production rate and watercut in the maturing assets. The present study has been conducted to assess the performance of stainless steel and the effect of various working conditions under high velocity (20ms-1) of liquid-solid jet impingement in various types of media containing 1.5wt% particles in normal water. Cumulative mass loss vs. exposure time was used to evaluate the erosion rate of the stainless steel. The surface and cross-sectional morphologies before and after the erosion tests were observed by scanning electron microscopy (SEM) to illustrate the evolution of erosion process. The effect of fluid impact angle on stainless steel depends on the competitive effect of normal stress and shear stress. Under normal impact, the surface film would be broken and damaged, but still remain on the electrode surface to provide somewhat protection. With the decrease of impact angle, shear stress becomes dominant, and it would thinner and even completely remove the film. The effects of impact angle on steel surface status and erosion rate are confirmed by surface morphology observation.