Amount Of Residual Stress Research Articles

Mechanical Proprieties and Residual Stress Evaluation on Heteroepitaxial 3C-SiC/Si for MEMS Application

SiC is a candidate material for micro- and nano-electromechanical systems (MEMS and NEMS). The hetero-epitaxial growth of 3C-SiC on silicon substrates allows one to overcome the traditional limitations of SiC micro-fabrication, but the high residual stress created during the film grow limits the development of the material for these applications. In this work, in order to evaluate the amount of residual stress released from the epi-film, different micro-machined structures were developed. Through the measurement of natural resonant frequencies and Raman shift analysis, a strong relationship between the mechanical proprieties of the material (Young’s modulus) and the film crystal quality (defect density) was observed.

Experimental Analysis of Residual Stresses in Cold Formed Truck Frame Side Rail Structures

One of the major applications for cold formed carbon steel ‘C’ sections is through load carrying structural frame side members in heavy road vehicles. Though it is expected that forming operations would enhance the mechanical properties of sections as a whole by strain-hardening, it leaves certain amount of residual stresses throughout the sections. It is thus necessary to account for the effect of residual stresses remaining from cold forming operations accurately, while assessing the mechanical behavior of truck side frame rail sections. In this work, an experimental investigation was carried out to assess residual stresses induced by cold forming operation of truck frame rail sections through X-ray diffraction method. Also an attempt was made to study the effect of shot-peening operation employed as a surface enhancement method on frame rail residual stresses.

The Study of Residual Stress in Welded Specimens of Aluminium Alloy by Using Acoustic Emission Method

Welding is one of the most significant causes of residual stresses and typically produces large tensile stresses whose maximum value can be approximately equal to the yield strength of the materials being joined. These large tensile stresses are often responsible for premature component failure. Metallurgical welding joints are extensively used in the fabrication industry, including ships, offshore structures, steel bridge, and pressure vessels. In this study, residual stresses in welded specimens of AL–6061 were evaluated by using ACOUSTIC EMISSION method which is one of the nondestructive tests. In this work, AE signals formed during the tensile test of welded specimens were investigated. The results show that AE signals in specimens which have large amount of residual stress were detected in less load.

The Influence of Retained Austenite on Residual Stresses in Laser Remelted Cast Iron

The presence and amount of residual stresses is very important in dynamically loaded automotive machine parts. In this investigation, the residual stresses after laser surface remelting were measured as a function of the modified layer depth on flat specimens from nodular cast iron. The results of the measured residual stresses confirm that the stresses strongly depend on the presence and quantity of the microstructure constituents in the surface remelted layer. Residual stresses have a characteristic profile in the modified surface layer. In the surface remelted layer, tensile residual stresses were found in a range between +70 and +200 MPa. The change from tensile into compressive residual stresses takes place in the lower part of the remelted layer. Maximum compressive residual stress values were found in the middle of the hardened layer in a range between 225 and 280 MPa.

Numerical study of springback using the split-ring test for an AA5754 aluminum alloy

The split-ring test provides a simple benchmark for correlating springback obtained by finite element analysis (FEA) with experimental measurements. This test consists in cutting a ring specimen from a full drawn cup and then to split the ring longitudinally along a radial plane. The difference between the ring diameters, before and after splitting, gives a direct measure of the springback phenomenon, and indirectly, of the amount of residual stresses in the drawn cup. In this paper, the numerical simulation of the deep drawing process and splitting of an aluminum alloy AA5754-O ring is performed using both the finite element code ABAQUS and the in-house code DD3IMP. The trimming of the ring is carried out with a devoted program, DD3TRIM, which allows the geometrical and material state remapping treatment of solid hexahedral element meshes. The punch-force evolution during deep drawing and thickness distribution obtained numerically are compared with experimental ones provided in [1] (Laurent et al., 2009). The influence of finite element formulation, mesh size and yield criteria on the numerical results for the ring opening is evaluated. The stress distributions in the cup, at the end of the drawing stage are analyzed and some explanations concerning their influence on springback mechanisms are given.

Some considerations about fatigue failure in milled butt-welded joints affected by residual stress

Many factors are involved in determining the fatigue strength of welded joints. It is, however, very difficult to consider their relative importance. The aim of this paper is to isolate the effect of residual stress from other factors, establishing a relation between the amount of residual stress and fatigue life. A geometrical notch due to the weld bead is removed by milling the upper surface of the welded plates. Moreover, specimens are subjected to four-point bend loading. Before conducting the fatigue test, the magnitude of residual stress for each specimen is experimentally evaluated, and then linked to the number of cycles to failure. This relation is analyzed for three different plate thicknesses and for different stress amplitude levels in the high cycle regime. The results clearly show the significant influence of residual stress on fatigue behaviours when the load level is near the fatigue limit.

Fine tuning straightening process using genetic algorithms and finite element methods

The process of straightening steel sections is used not only to actually straighten the product but also to reduce its internal residual stresses. Fine tuning this process within an industrial plant is complicated because of the time needed for conducting the tests and the difficulties in measuring the final residual stresses. This paper presents a methodology based on genetic algorithms and finite element analysis that seeks the best position of the rollers to produce a straightened product with the minimum amount of residual stresses. The process consists of simulating multiple roller positions using a previously validated finite element model and analysing the resulting residual stresses. Genetic programming is used to choose the best solutions that will give rise to the next generation of individuals. For several generations, the system combines a series of optimum solutions in which residual solutions are minimised. The best solutions obtained enable the rollers to be positioned in a way that guarantees a good end quality for the product.

EFFECT OF COMPRESSIVE RESIDUAL STRESS INDUCED DURING FABRICATING PROCESS IN THE CORE OF CLAMPED SANDWICH PLATE UNDER SHOCK LOADING

Sandwich panels can be manufactured in many ways like lamination press, closed mold fabrication, and vacuum bag compaction. During manufacturing, the core and the sheets are attached under certain applied pressure and temperature, associated with a deformation and stress remaining in the sandwich core. This study presents an evaluation of the compressive residual stress effect of the core which occurs during the localized shock loading at the mid-span of a clamped sandwich plate. We simulate such a square lattice core sandwich plate by commercial finite element code, ABAQUS/Explicit. We apply uniform distributed loading on upper face sheet and temperature difference occurred during the manufacturing process is taken here before the impact simulation step. These loadings induce certain amount of residual stresses in core structure of sandwich panel. The computational result from non-residual stress case is verified by comparing with the results of published experimental data on similar investigation. In addition, the effect of existing residual stress at core is analyzed. We also compare the dynamic responses of two clamped sandwich plates with and without pre-stressed core. And impact resistance of sandwich panel is explained in the view of energy capacity. Results show that the shock loading behavior of sandwich panel depends on its manufacturing process and panels with compressive residual stresses have less deformation and high impact energy absorption characteristics.

Mechanical characterization of glass/polyimide microjoints fabricated using cw fiber and diode lasers

This paper discusses the laser-irradiated microjoints between glass and polyimide for applications in neural implants. To facilitate bonding between them, a thin titanium film with a thickness of approximately 0.2 μm was deposited on glass wafers using the physical vapor deposition (PVD) process. Two sets of samples were fabricated where the bonds were created using diode and fiber lasers. The samples were subjected to tension using a microtester for bond strength measurements. The failure strengths of the bonds generated using fiber laser are quite consistent, while a wide variation of failure strengths are observed for the bonds generated with diode laser. Few untested samples were sectioned and the microstructures near the bond areas were studied using an optical microscope. The images revealed the presence of a sharp crack in the glass substrate near the bond generated with the diode laser. However, no such crack was observed in the samples made using fiber laser. To investigate the reasons behind such discrepancy in bond quality further, uncoupled three-dimensional finite element analyses (FEA) were conducted only for the samples created using diode laser. First, the transient heat diffusion-based FEA was conducted by using the laser power intensity distribution as a time dependent heat source. This model calculates the temperature distribution within the substrates as a function of time. Next, the structural model predicts the amount of residual stresses developed in the joint system as it is cooled down to room temperature. The out-of-plane normal component of residual stresses was within the failure strength range of glass that may have caused fracture initiation in the substrate.

Influence of Residual Stresses on the Wear Behavior of Alumina/Alumina–Zirconia Laminated Composites

Symmetric structures of laminated ceramic composites were produced by superimposing alternating layers of Al2O3 and Al2O3/ZrO2 composite prepared by tape casting. The composites were designed to have an alumina surface layer on either side. This configuration caused residual compressive stresses to be induced on the surface due to the different thermal expansion coefficients of the various layers, leading to an increase in the apparent surface toughness. The amount of residual stress was determined using the indentation technique. The tribological behavior of these laminated structures was evaluated using the pin‐on‐disk method for different loads and sliding speeds. Comparison with the results obtained from stress‐free alumina showed that, within the range of these experimental conditions, the improvement in surface toughness leads to a reduced friction coefficient and increased wear resistance of the composites. Possible wear mechanisms are proposed.

Lower and upper shakedown bounds for fatigue limit in two phase materials

The goal of this study is to find the ‘safe’ long term behavior of elasto-plastic structural materials subjected to fluctuating load (shortly ‘fatigue limit’). The materials whose fatigue limits are checked are: (a) materials reinforced with unidirectional stiff fibers; (b) materials with dilute amount of inclusions; (c) materials with minute porosity. To reach this goal we employ two different shakedown theorems: Melan’s static shakedown theorem (1936) as the lower bound and Koiter’s kinematic shakedown theorem (1960) as the upper bound. The solutions to the lower and upper bounds for the prescribed stress amplitude, (Δσ th) l,b. and (Δσ th tu.b. , are expressed in a rigorous form with three parametric entities: (i) the volume fraction of the second phase in the base matrix phase, f, (ii) the quality of the ‘bond’ between the two phases ‘m’, (iii) the magnitude of the residual stress, ‘p’, pre-existed in the material. The deviation between the two bounds represents the ‘uncertainty’ in our knowledge of the actual safe/unsafe state, where the materials fail to withstand the alternating load. It is shown that in the considered three types of materials, at certain amount of residual stresses, the safe load amplitudes based on shakedown analysis are indeed higher than their corresponding elastic limits (at least by 5%, 10% and 25% respectively). The apparent advantage of using shakedown bounds to predict the safe/unsafe loading amplitude is that no prior information on the actual complex failure mechanisms is required and no empiricism is needed. However, empirical data which were found in the open literature are ‘falling’ satisfactorily between the computed dual bounds.

Energy release rate analysis for adhesive and laminate double cantilever beam specimens emphasizing the effect of residual stresses

The mode I energy release rate, including the effect of residual stresses, was evaluated for both adhesive and laminate double cantilever beam specimens. The energy release rate can be partitioned into a mechanical term and a residual-stress term in beam theory. The beam-theory mechanical term is not very accurate, but can be corrected by a slight modification to a previous correction factor. This correction factor accounts for crack tip rotation of the specimen arms. The beam-theory residual-stress term is very accurate for a wide range of specimen geometries; it can be used without correction. The consequence of ignoring residual stresses is that one measures an apparent toughness instead of a true toughness. The error between the apparent toughness and true toughness can be calculated for a given specimen geometry and amount of residual stresses. Such errors can be large and are often larger than the correction required for crack-tip rotation effects. In double cantilever beam specimens used to study laminate delamination, the errors are large when the delaminating arms, considered by themselves, are unsymmetric laminates. Some experimental methods are suggested which can be used to correct for residual stress effects.

The Effect of Solution pH and Heat‐Treatment on the Properties of Electroless Nickel Boron Films

Electroless nickel boron films were investigated using metallizing solutions of various pH's and heat‐treatments at different temperatures. Solution pH controls the boron content in the as‐deposited films which in turn acts as a crystallization inhibitor. Heat‐treatments at different temperatures all result in the formation of face centered cubic nickel crystallites of varying dimensions and causes the migration of boron to the surface. Using radial distribution function techniques, the amount of residual stress in these films was also determined.

Some aspects of deformation behavior of coarse multiphase metallic materials

The deformation behavior of several single-and two-phase coarse microstructures has been examined using microhardness measurements. It has been found that the strength response of a coarse phase in isolation is distinctly different from its response when it exists in a two-phase system. The second phase alters the mechanical state of the first one andvice versa even in the plastically undeformed condition. This phenomenon is explained in terms of the existence of an appreciable amount of residual stresses in two-phase coarse microstructures. These stresses primarily arise due to the difference in thermal expansion coefficients of the phases. The influence of elastic stress field on microhardness response is shown with a new type of experiment to support the proposed explanation. The present results question the existing expressions for deformation modeling of multiphase materials because of the uncertainties in the estimation of the average strength of the phases in a two-phase system.

陶材焼付連結冠の適合性の変化に関する研究

In manufacturing ceramo-metal restoration, the metal coping is subjected to several mechanical and thermal treatments after cast for fusing porcelain. Several reports have demonstrated some changes in the fit of the single ceramo-metal crown during such procedures. The potential disturbance of the fit in the case of the connected crowns was examined in this study. The model was composed of two abutments for connected crowns with an interspace of 1 mm. Both the abutments were of shouldered type, 6 mm in height and 5°in taper. The pattern was prepared using a spacer to ensure the specified thickness for full-baked or veneered type. The investments used were two brands of phosphate-bonded investments-Uni vest non-precious (UN) and Blue vest (BV) having different compressive strength. Nickelchromium alloy was employed as the coping metal. The vertical gap at the margin between the coping and the abutment shoulder was measured after each stage of the procedures : casting, cutting of sprue, treating of metal surface, degassing, fusing of opaque porcelain, fusing of body porcelain, adjusting of body porcelain, and glazing. The as-cast connected crowns were in mesio-distally warped shape showing larger gap at the proximal margin than at the connected margin. The subsequent mechanical and thermal treatments caused deformation of the crowns to correct the warpage to some extent, resulting in the decreased gap as a whole. The largest decrease in the gap was generally found at the stage of sprue cutting, and the second at those of degassing and sandblasting for metal surface treatment. The decrement at each stage was changed by altering the processing order in association with the amount of residual stresses in the casting involving uncut sprue and runner bar, relaxation and release of the stresses, and development of new stresses in the previous treatments. The changes in the fit were marked in the full-baked type with the coping being thinner, especially cast with the investment UN when compared with that in the veneered-type. It is because a larger residual stress might be introduced in the casting with use of the stronger investment UN than BV, which was suggested from the cast tearing test. The compressive strength of BV is intentionally lowered by the manufacturer for the purpose of making it easy to take out the casting from the mold. The lowered strength of this investment showed additional effect of reducing the residual stress and hence minimizing the fit changes in the subsequent procedures. The application of the stress relief annealing to the casting before cutting the sprue was also found to be effective for maintaining the as-cast fit of the casting.

Characterization of Lead Zirconate Titanate (PZT) - Indium Tin Oxide (ITO) Thin Film Interface

ABSTRACTThe interface between ultrathin sputtered lead zirconate titanate (PZT) films and a conductive electrode (indium tin oxide-ITO) is investigated. Structural and compositional changes at the PZT-ITO interface have been examined by surface analysis and depth profiling techniques of glancing angle X-ray diffraction, Rutherford backscattering (RBS), SIMS, Auger electron spectroscopy (AES), and elastic recoil detection analysis (ERDA). Studies indicate significant interdiffusion of lead into the underlying ITO layer and glass substrate with a large amount of residual stress at the interface. Influence of such compositional deviations at the interface is correlated to an observed thickness dependence in the dielectric properties of PZT films.

工業用純アルミニウム１０５０の低温における引張り性質

Effect of test temperature on tensile properties of 1050 aluminum plate has been investigated at temperatures ranging from 473K to 4K for four kinds of specimens which are as rolled, recovered, partially recrystallized or fully recrystallized. The results obtained are as follows;1. Deformation is more unifrom at 4K than at temperatures above 77K resulting in a marked increase in the elongation to fracture at 4K.2. Proof stress increases almost linealy with decrease in test temperature, though there exists clear difference in the temperature dependence between fully recrystallized specimens and the specimens including a certain amount of residual stress.3. Below 200K all specimens show the parabolic increase in the ultimate tensile strength with decrease in the test temperature. The as rolled specimen only tends to neck at 4K and at strain rate of 3.3×10-4s-1. The temperature dependence of ultimate tensile strength corresponds to the difference in residual stress and microstructures.

Effect of transformation temperature range on generation of thermal stress and strain during quenching

Composition varies sufficiently widely within an alloy specification to allow significant variations in the temperature ranges within which the austenite phase transforms to martensite. It has been suggested that such variations in composition are associated with anomolous fluctuations in the distortions produced in quenched components of a particular alloy. In the present work, a plane stress infinite plate mathematical model was used to conduct a quantitative examination of the connection between these compositional variations, the associated changes in the Ms and Mf temperatures, and the amount of residual stress and strain after quenching. The residual strains at the end of a water quench increased substantially as the Ms temperature increased. However, the corresponding stresses after the same water quench and both the residual stresses and strains at the end of an oil quench were only slightly affected by such changes in the Ms temperature. This displacement in the temperature range within which transformation occurred reduced the absolute value of the transformation strain, one of the components contributing to total strain. At the end of the quench the sum of the other strain components was positive and larger than the negative transformation strain, so the reduction in the absolute value of the latter, associated with the increase in the Ms temperature, led to the increase in the residual strain at the end of the quench. The results obtained support the suggestion that the limitations of fluctuations in composition within the alloy specification are beneficial to the control of distortion in quenched components, although the most desirable compositions are those that produce a lower rather than a higher Ms temperature.MST/367

Residual stress in coated low-z films of TiC and TiN: II. correlation of residual stress with microstructure

The correlations of the residual stresses with microstructures of TiC and TiN films deposited onto various substrates were examained by means of observations of SEM micrographs, X-ray back-reflected Debye rangs and diffraction line profile of X-ray spectorometer chart. It was found that specimens with lower residual stress generally show sharp line profile and good separation between K α2 and K α2 diffraction peaks in both TiN and TiC films, indicating better crystalline perfection. PVD coated TiC films on Mo and Inconel substrates show poor separation of K α2 and K α2 peaks, namely due to higher residual stresses in comparison with those of CVD coated TiN and TiC films on Mo or Inconel substrate. In CVD TiC/Pocographite system, with film thickness ranging from 10 to 100μm, the grain size increase with increasing the thickness, except 100μm thick specimen which has the smallest grain size in this group. However, the sharpness of diffraction profile is best in 20μm thick film, and worst in 100μm thick film. This is in good correlation with the amount of residual stress.

Increased fracture toughness of ceramics by energy-dissipative mechanisms

A theoretical model for the fracture toughness of ceramics is developed which takes into account such energy-dissipative mechanisms as stress-induced microcracking or phase transformation. To establish the general fracture criterion, a Griffith-type energy balance is employed. This energy balance comprises the elastic energy, the fracture surface work consumed in the process zone at the crack tip, the energy dissipated in the dissipation zone and the energy stored by residual stresses. Stress-induced microcracking is considered in more detail. An expression for the dependence of the fracture toughness on the density of microcracks, the amount of residual stresses caused by thermal expansion mismatch between the ceramic matrix and small particles embedded in it and the volume fraction of these particles is derived. The final results are used to state conditions necessary for the fracture toughness to be increased. The theory agrees well with experimental results taken from literature (alumina with zirconia particles).