Effects Of Surface Residual Stress Research Articles

Nonlinear fracture mechanics analysis of nano-scale piezoelectric double cantilever beam specimens with surface effect

Abstract A fracture mechanics analysis model for the piezoelectric double cantilever beam (DCB) fracture specimens is developed. The model incorporates residual surface stress, surface elasticity and surface piezoelectricity and considers the finite deformation theory. Based on Timoshenko beam theory, the governing equation is derived and solved numerical. Consideration of geometrically nonlinear deformation will significantly decrease the prediction of energy release rate. The effects of residual surface stress and surface elasticity on the energy release rate is more significant for a thinner beam. The influence of surface residual stress on the energy release rate depends on the length to thickness ratio of the DCB. For open-circuit boundary condition, the applied voltage and surface piezoelectricity can affect the energy release rate, and the effect of surface piezoelectricity is more obvious for a thinner beam. However, for short-circuit boundary condition the surface piezoelectricity cannot affect the energy release rate.

Effects of Surface Residual Stress on the Local Indent Strain

Effects of Surface Residual Stress on the Local Indent Strain

Study on Tension-Compression Fatigue Properties of Hard Machined Components

Hard turning and fatigue tests are conducted to study the influence of cutting process on the fatigue properties of hard machined components in this work. The specimens are machined under various cutting speeds and tool wear condition. Tension-compression fatigue tests of the specimens are performed. The typical fatigue fracture patterns are observed and discussed. The fatigue life of the specimens is recorded and compared. The mechanism of the influence of white layer on fatigue properties is proposed, and the effects of white layer on the fatigue life are obtained. The changing process of tensile and compressive residual stresses is discussed. The effects of surface residual stress and maximum residual stress on the fatigue life are clarified.

FEM Study and Characterization on Laser Shock Peening of TC4 Titanium Alloy Structure

This paper, using the finite element software ABAQUS, establishes the model of laser shock peening (LSP) of TC4 titanium alloy, and analyzes the influence of different parameters on the residual stress of TC4 titanium alloy and plastic deformation. The results show that LSP can make the surface of TC4 titanium alloy have large compressive stress and plastic deformation, hardness and prolong the fatigue life of materials. Laser energy and the impact frequency are the main factor of surface residual stress effects. The multi-point LSP can perform processing enhanced in surface area, and form residual compressive stress on the surface of the material and in a certain depth.

Finite element modeling for elastic nano-indentation problems incorporating surface energy effect

Abstract Nano materials have attracted considerable attention during the last two decades, due to their unusual electrical, mechanical and physical properties as compared with their macro counterparts. Mechanical properties of nano materials show strong size-dependency, which has been explained within the framework of continuum mechanics by including the effects of surface residual stresses and surface elasticity as introduced by Gurtin and Murdoch (GM) theory of surface elasticity. In the present work, a finite element model, based on the principle of minimum total potential energy, is developed to monitor the behavior of two-dimensional nano size structures, taking into account the surface effects according to the complete GM model, under elastic frictionless indentation process. Different from most of literature, the presented FE model is capable of solving a variety of problems no matter the complexity of the punch geometry or the boundary conditions. For the sake of comparison as well as validation, the developed model is used for analyzing a simple plane strain problem, and the obtained results have been compared with analytical results published in cited literature. Several problems with different surface-energy model assumptions, indenters of different geometrical shapes and different sizes of indented bodies are solved, to examine its size dependency. The non-conformal contact between the indenter and the elastic half plane is solved, in the context of contact mechanics, by the incremental convex programming (ICP) method.

The effect of surface elasticity and residual surface stress in an elastic body with an elliptic nanohole

The deformation of an elastic plane with an elliptic hole in a uniform stress field is considered, taking into account the surface elasticity and the residual surface tension. The solution of the problem, based on the use of the linearized Gurtin–Murdoch surface elasticity relations and the complex Goursat–Kolosov potentials, is reduced to a singular integrodifferential equation. Using the example of a circular hole, for which an exact solution of the equation is obtained in closed form, the effect of the residual surface tension and the surface elasticity on the stress state close to and on the boundary of a nanohole is analysed for uniaxial tension. It is shown that the effect of the residual surface stress and the surface tension, due to deformation of the body, depends on the elastic properties of the surface, the value of the stretching load and the dimensions of the hole.

Surface Integrity and Fatigue Behavior for High-Speed Milling Ti–10V–2Fe–3Al Titanium Alloy

Influence of cutting parameters on surface integrity when milling Ti–10V–2Fe–3Al is investigated based on high-speed cutting experiments. Surface integrity measurements, fatigue fractography analysis, and fatigue life tests are conducted to reveal the effect of surface integrity on crack initiation and fatigue life. The results show that under given experiment conditions, surface roughness decreases linearly when increasing cutting speed or decreasing feed per tooth. The latter has a greater impact on surface roughness than the former. Compressive stress can be detected on all machined surfaces. With the increase of feed per tooth or cutting speed, respectively, residual stress presents a linear increase. Cutting parameters have no significant impact on micro-hardness. When the surface roughness ranges from 0.5 to 1.0 μm, the effect of surface residual stress on fatigue life is more than that of surface roughness. When the surface residual compressive stress increases, the fatigue life improves significantly. Compared with 60 m/min, when cutting speed is 100 or 140 m/min, the surface roughness decreases, the surface residual compressive stress increases, and the fatigue life improves by 124 and 59%, respectively. Under a tensile load, fatigue crack on machined surface of Ti–10V–2Fe–3Al titanium alloy originates at the cross-edge of the specimen surface. With the increase of surface roughness, the area ratio of fatigue crack propagation zone, and fatigue fracture zone decreases.

Effect of crack face residual surface stress on nanoscale fracture of piezoelectric materials

This paper investigates the problem of a nanoscale crack in piezoelectric nanomaterials by considering the effect of the residual surface stress on the crack surface. The solution of problem is obtained by the singular integral equation technique. The study of the fracture mechanics parameters confirms the fact that nanomaterials are crack-insensitive. It is also found that the effect of surface on the electric displacement intensity factor depends on the crack face electric boundary condition. Moreover, the electromechanical coupling fracture behavior of the piezoelectric materials is influenced by the residual surface stress on the entire crack surface.

Effect of surface residual stress on the fracture of double cantilever beam fracture toughness specimen

This paper studies the influence of surface residual stress on the fracture of the double cantilever beam (DCB) specimens. The closed-form solutions of the energy release rate and the stress intensity factor are derived by using Timoshenko beam theory. Results show that positive residual surface stress and the root effect of the DCB enhance the energy release rate and the stress intensity factor. The root effect cannot be neglected if the thickness of the beam is at the nanoscale (e.g., less than 100 nm), even though the ratio of beam length to thickness is larger.

Effects of residual surface stress and surface elasticity on the nonlinear free vibration of nanoscale plates

This paper studies the influence of surface effects (including the residual surface stress and surface elasticity) on the nonlinear free vibrations of nanoscale plates. The motion equations are derived by using the Hamilton’s principle and solved numerically. It is found that the influence of surface effects on the normalized period of nanoscale plates becomes increasingly significant when the thickness of the plate decreases. More importantly, the influence of the surface effects on the normalized vibration period reduces if the initial amplitude of the vibration increases. This tendency is more pronounced for the Mindlin plate theory, which includes the transverse shear effect of the plates. In addition, it is found that both the positive residual surface stress and surface elasticity increase the magnitude of the vibration velocity.

Effect of residual surface stress on the fracture of nanoscale materials

The problem of a mode I crack in nanomaterials under a remote mechanical load is investigated. The effect of the residual surface stress on the crack surface is considered and the solutions to the crack opening displacement (COD) and the stress intensity factor (KI) are obtained. The results show that the surface effect on the crack deformation and crack tip field are prominent at nanoscale. Moreover, COD and KI are influenced by the residual surface stress not only on the surface near the crack tip region but also on the entire crack surface.

Effect of surface finishing and loading condition on competing failure mode of clean spring steel in very high cycle fatigue regime

The effect of surface finishing and loading condition on competing failure mode of a newly developed spring steel, SUP7-T386, in very high cycle fatigue (VHCF) regime was experimentally studied. As a result, this steel for ground specimen represents the duplex S–N characteristics under rotating bending and the continuously descending S–N characteristics under axial loading, respectively, and all corresponding to surface and interior failure, whereas that for electro-polished specimen represents traditional S–N characteristics with a clear fatigue limit, only corresponding to surface failure. Owing to the combined effect of stress gradient and surface residual compressive stress, as well as the larger size of inhomogeneous microstructure (IM), the interior inclusion-induced failure with fine granular area (FGA) and the interior IM-induced failure without FGA become the predominant failure mode of this steel for ground specimen under rotating bending and under axial loading in VHCF regime, respectively. The threshold stress intensity factor for controlling surface and interior small defect-induced crack propagation of this steel is evaluated to be 2.86MPam1/2 and 2.04MPam1/2, respectively, the short crack effect plays a key role in causing the small defect-induced failure of this steel in VHCF regime. Considering the effect of surface residual stress, the surface fatigue limit of this steel can be well evaluated by the size of inclusion or IM. For the evaluation of interior fatigue limit of this steel, it is suitable by the size of IM under axial loading but it is all conservative by the size of inclusion, or IM and or FGA under rotating bending.

Effects of surface residual stress and surface elasticity on the overall yield surfaces of nanoporous materials with cylindrical nanovoids

Mechanical properties of a material near the surfaces and interfaces are different from those of the same material far from the surfaces/interfaces. The effect of this difference on the effective mechanical properties of heterogeneous materials becomes significant when the size of inhomogeneities is at the scale of nanometers. In this article, within a micromechanical framework, the effects of surface residual stress and surface elasticity are taken into account to obtain a macroscopic size-dependent yield function for nanoporous materials containing aligned cylindrical nanovoids. Based on the modified Hill’s condition, the strains are decomposed into two parts, a part due to the external loadings and another part due to the surface residual stress. Then, using the size-dependent effective elastic moduli of the material, an overall yield function is derived. The yield function then is simplified for different practical loading conditions. In addition, considering some numerical examples of metal matrices with nanoporosity, it is shown that the surface stress, including the surface residual stress, has a significant influence on the yielding of these materials with voids of radii smaller than 50nm. The results show that the effect of the surface residual stress is much more important than the surface elasticity effect, and it should be considered in estimating the yield strength of nano-heterogeneous materials.

Surface Effects on the Jump-in Instability of Nanomechanical Structures

Surface effects are indispensable for crystalline materials when the characteristic size falls into nanoscale. In this paper, the size-dependent jump-in instability of an ultrathin film, omnipresent in nanoelectromechanical systems, is analyzed by incorporating the effects of surface energies. Based on a nonclassical thin plate theory including surface effects and the thermodynamic energy balance theorem, the jump-in instability mechanism of the film is established to determine the critical separation gap and contact length between the film and the substrate. We found that the dimensionless forms of these two mechanical properties depend on the thickness of the film. When the residual surface stress is ignored, the critical separation gap is affected by the surface elasticity, but the contact length is not. An aluminum film is considered as an illustrative example, for which the effect of residual surface stress is superior to that of surface elasticity.

Vibration characteristics of circular nanoplates

This article deals with free vibration of circular nanoplates with consideration of surface properties due to high surface to volume ratio. Classical laminated plate is employed with inclusion of surface elasticity and surface residual stress effects. Solution of the resulting differential equation leads to size dependent behavior of natural frequencies and mode shapes of vibration to be demonstrated. Deviation of the results from conventional theories is shown to be due to changes in the arguments of Bessel functions in the corresponding characteristic equations.

Effects of local surface residual stresses on the near resonance vibrations of nano-beams

The effects of surface residual stresses on nano-beams including mid-plane stretching under near resonance vibrations, are studied. The nonlinear vibration equations are separated into two complementary parts: static, which includes the surface residual moments and yields a residual deflection, and dynamic, for the beam vibrations associated with the residual deflection via geometrical nonlinearity. The dynamic response is expressed by a shape mode expansion with time dependent coefficients, governed by a set of coupled ordinary differential equations. An approximated solution is extracted analytically by a combination of the asymptotic straight-forward expansion and multiple scale method. Results exhibit fine correspondence with finite element simulations. It is found that the non-uniformities in the surface residual stresses change the resonance frequency of the beam, shifts its amplitude-response curve and reduce its phase. Applications for nano-sensors are demonstrated and optimization possibilities are discussed.

Effect of residual surface stress and surface elasticity on deformation of nanometer spherical inclusions in an elastic matrix

The analytical solution of the Eshelby problem, which describes the deformation of an elastic medium inside and outside a spherical inclusion with uniform internal eigenstrain and specified remote stress, is generalized taking into account both surface elasticity and residual surface stress. Expressions are derived for the internal and external Eshelby tensors and stress concentration tensors with regard to the above effects. A characteristic strain field inhomogeneity and its dependence on the inclusion diameter in the nanometer range (the scale effect) are found. It is shown that under certain conditions, the effect of residual surface stress surpasses that of surface elasticity.

Timoshenko beam model for static bending of nanowires with surface effects

In this paper, surface effects on the elastic behavior of static bending nanowires (NWs) are studied by using a comprehensive Timoshenko beam model. For NWs with different boundary conditions, explicit solutions are derived to study the combined effects of residual surface stress, surface elasticity and shear deformation on the effective stiffness and Young's modulus of the NWs. The stiffness is found to be size-dependent and this dependence is more significant for slender NWs. Residual surface stress tends to increase or decrease the stiffness of NWs depending on their boundary conditions, and the shear deformation always makes the NWs softer compared with the results of the Euler–Bernoulli beam model. The solutions agree well with experimental measurement in predicting the Young's modulus, especially for NWs with small length-to-thickness ratio. This work might be helpful for characterizing the mechanical properties of NWs and the design of nanobeam-based devices.

Effect of surface residual stress and inclusion size on fatigue failure mode of matrix HSS in very high cycle regime

Fatigue properties in high cycle and very high cycle fatigue regime of matrix high-speed tool steel (1.3C-6W-5Mo-3V-8Co) were investigated through the experimental results obtained from a cantilever-type rotary bending fatigue test in air at room temperature using hourglass shaped specimens. Two kinds of specimen were processed by grinder and cutting tool, which led to different surface compressive residual stress. Both specimens showed clear duplex S-N curve, composed of three or two types of failure mode depending on the stress amplitude, such as, a surface inclusion-induced failure mode (S-mode), a subsurface inclusion-induced failure mode without (I-mode) and with granular bright facet (GBF) area in the vicinity of inclusion (IGmode). The transition of the failure mode from S-mode to I-mode and from I-mode to IG-mode was occurred at high stress amplitude level by the effect of large compressive residual stress on the surface layer. A map of the appearance of failure modes relating the stress amplitude with the residual stress was proposed and showed a good agreement with the experimental results. Fatigue life in very high-cycle regime was almost same between the both specimens because of the existence of almost same size inclusion at crack origin. S-N curve depended on the inclusion size was provided with the estimation of crack growth rate from the S-N data.

Effect of Grinding Induced Damage on Bending Strength of RBSiC

The effect of surface residual stress and crack on bending strength of reaction bonded silicon carbide(RBSiC) after grinding was investigated.The residual stress of the ground surfaces were determined using X-ray diffraction.The sizes of strength controlling cracks were assessed using fracture mechanics approach.The investigations show that mechanical load,which has relation with grinding direction,phays a dominateve role in the grinding processes.and the measured residual stresses have a direction dependency.With increase of down feed from 0.9μm/s to 1.35μm/s,the bending strength is reasonably correlated with the surface residual stress and crack size.