Decrease In Maximum Stress Research Articles

Simulated crack propagation in cemented total hip replacements

The purpose of this investigation was to determine the specific fracture mechanics response of cracks that initiate at the stem–cement interface and propagate into the cement mantle. Two-dimensional finite element models of idealized stem–cement–bone cross-sections from the proximal femur were developed for this study. Two general stem types were considered: rectangular shape and Charnley type stem designs. The FE results showed that the highest principal stress in the cement mantle for each case occurred in the upper left and lower right regions adjacent to the stem–cement interface. There was also a general decrease in maximum tensile stress with increasing cement mantle thickness for both rectangular and Charnley-type stem designs. The cement thickness is found to be one of the important fatigue failure parameters which affect the longevity of cemented femoral components, in which the thinner cement was significantly associated with early mechanical failure for short-time period.

Influence on the microstructure and properties of AZ61 magnesium alloy at warm deformation

Abstract Thermal compression tests of AZ61 magnesium alloy were performed at deformation temperature 423–673 K and strain rates ranged from 0.01 to 10 s−1, and the microstructure was studied. The result shows that dynamic recrystallization (DRX) happened under the warm deformation of AZ61 alloy. One hand, the values of maximum stress decrease when the deformation temperature increases, and the grain size grows up. On the other hand, the critical strain increases with the strain ratio increase. Therefore, temperature and strain ratio can make a great effect on the microstructure and mechanical properties of AZ61 alloy, but temperature is the more important factor.

数値解析によるコークス強度に関する微視構造支配因子の特定

To investigate the effect of microscopic structures on coke strength, the stress analysis using a homogenization method is carried out for coke with different microscopic textures and pores with various shapes. Analytical results show that stress concentration for pores affects stress field in microscopic region of coke, on the other hand, the diameter and arrangement of inert in coke matrices hardly affects the stress field. The stress concentration for pores is the main factor of lowering coke strength since the interference of the stress concentration causes an increase in the maximum stress and a decrease in the homogenized elastic modulus. Especially, the existence of pores with low roundness causes a decrease in the homogenized elastic modulus of coke drastically and its effect on coke strength is bigger as the pore size is larger. Thick pore wall gives a decrease in maximum stress and an increase in the homogenized elastic modulus. In addition, in the case of pores with low roundness, the existence of big pores counteracts an increase in the homogenized elastic modulus with thick pore wall.

Biomechanical finite element analysis of bone cemented hip crack initiation according to stem design

The purpose of this investigation was to determine the specific fracture mechanics response of cracks that initiate at the stem-cement interface and propagate into the cement mantle. Two-dimensional finite element models of idealized stem-cement-bone cross-sections from the proximal femur were developed for this study. Two general stem types were considered; Rectangular shape and Charnley type stem designs. The FE results showed that the highest principal stress in the cement mantle for each case occurred in the upper left and lower right regions adjacent to the stem-cement interface. There was also a general decrease in maximum tensile stress with increasing cement mantle thickness for both Rectangular and Charnley-type stem designs. The cement thickness is found to be one of the important fatigue failure parameters which affect the longevity of cemented femoral components, in which the thinner cement was significantly associated with early mechanical failure for shot-time period.

Deformation behaviour of ultrafine-grained magnesium with 3 vol.% graphite

Abstract Magnesium micropowder was mixed and ball-milled with 3vol.% graphite powder. The Mg+Graphite composite was deformed in compression at temperatures between room temperature and 300°C at a constant crosshead speed, giving an initial strain rate between 1.4 · 10−5 and 1.4 · 10−3s−1. The yield stress of the composite is higher than that of unreinforced magnesium prepared with the same technology. The yield stress and the maximum stress decrease rapidly with increasing temperature. At temperatures higher than room temperature, the true stress–true strain curves exhibit a work-hardening rate close to zero, which indicates a dynamic equilibrium between hardening and softening. Double cross-slip of screw components of c+a dislocations is considered as the main recovery mechanism.

Effects of high-pressure acclimatization on silver eel ( Anguilla anguilla, L.) slow muscle contraction

As the spawning migration of the eel is supposed to correspond to a long swimming activity at depth, patterns of slow red muscle contraction have been investigated in European silver eel ( Anguilla anguilla L.) exposed for 3 weeks to 10.1 MPa hydrostatic pressure. The results show that pressure-acclimated eels (male and female) show a three-fold decrease in maximum isometric stress of twitch and tetanic contractions while time to peak force, time from peak force to 90% relaxation and ratio of twitch tension to tetanic tension remain unchanged. The observed modifications in slow red muscle mechanical properties do not impede the spawning migration of the eel and are possibly partially compensated by an improvement in the efficiency of oxidative phosphorylation. Effects of changes in membrane fluidity are also discussed.

Mechanical Properties of AS21 Magnesium Alloy Based Composites

The high temperature behaviour of composites with the AS21 magnesium alloy matrix, reinforced by short Saffil fibres was investigated in the temperature interval from room temperature to 300 °C. The yield stress and the maximum stress decrease with increasing temperature. Two types of specimens were investigated – one with fibres plane oriented parallel to the stress axis and the other with perpendicular fibres plane orientation. Light and scanning electron microscopy were used for study of the microstructure of composites. Possible hardening and softening mechanisms are discussed. The shear stress at fibre/matrix interface was of greatest importance in this regard, though the contribution resulting from the dislocation density increase was also significant.

Deformation behaviour of an AS21 alloy reinforced by short Saffil fibres and SiC particles

The high temperature behaviour of composites with the AS21 magnesium alloy matrix reinforced with short Saffil fibres and SiC particles were investigated in the temperature range from room temperature to 300 °C. The yield stress and the maximum stress decrease with increasing temperature. Two types of specimens were investigated – one with fibres plane oriented parallel to the stress axis and the other with perpendicular fibres plane orientation. Light and scanning electron microscopy were used for study of the microstructure of composites. Possible hardening and softening mechanisms are discussed. The shear stress at reinforcing phase/matrix interfaces was of greatest importance in this regard, though the contribution resulting from the dislocation density increase was also significant.

Correlation between Residual Stress and Boron Concentration in Boron-Doped Silicon Films

This paper represents the correlation between the residual stress and the boron concentration in boron-doped silicon films. Residual stress measurement structures of different thicknesses are simultaneously fabricated for the quantitative determination of residual stress profiles. All structures are diffused by various boron diffusion processes and consecutively etched by an improved etch process on the same silicon wafer. The obtained residual stress profiles illustrate that as the drive-in process temperature or the time increases, the average residual stress and the maximum residual stress decrease. For cases of several drive-in process conditions, correlation coefficients between the boron concentration and the residual stress are calculated and the lattice contraction of a boron-doped silicon wafer is measured by high-resolution X-ray diffractometry(HRXRD). The calculated correlation coefficients illustrate that the residual stress profile is closely correlated with the boron concentration after drive-in.

Parecoxib Impairs Early Tendon Repair but Improves Later Remodeling

Background Cyclooxygenase-2 inhibitors inhibit bone repair. Hypothesis Cyclooxygenase inhibitors might also have a negative effect on early tendon repair, although a positive effect on late tendon repair previously has been shown. Study Design Controlled laboratory study. Methods Achilles tendon transection was performed on 80 rats. Sixty rats were given daily intramuscular injections of either parecoxib (6.4 mg/kg body weight) or saline for the first 5 days after surgery and sacrificed either at 8 or 14 days. The remaining 20 rats were given intramuscular parecoxib or saline injections from day 6 until sacrifice at 14 days. Results At 8 days, early parecoxib treatment caused a 27% decrease in force at failure (P = .007), a 25% decrease in maximum stress (P = .01), and a 31% decrease in energy uptake (P = .05). Stiffness and transverse area were not significantly affected. At 14 days, early parecoxib treatment caused a decrease in stiffness (P = .004). In contrast to early treatment, late parecoxib treatment caused a 16% decrease in cross-sectional area (P = .03) and a 29% increase in maximum stress (P = .04). Conclusions During early tendon repair, a cyclooxygenase-2 inhibitor had a detrimental effect. During remodelling, however, inflammation appears to have a negative influence, and cyclooxygenase-2 inhibitors might be of value. Clinical Relevance The results suggest that cyclooxygenase-2 inhibitors should be used with care in the early period after tendon injury.

Tensile properties of hot rolled AZ31 Mg alloy sheets at elevated temperatures

Mechanical properties of commercial wrought AZ31B magnesium alloy sheets were investigated by tensile tests at various temperatures between room temperature and 400 °C at a strain rate of 1.3×10 −4 s −1. The yield stress and the maximum stress decrease with increasing temperature. The ductility increases very rapidly with increasing temperature. The results are explained by the dislocation glide in the basal and non-basal slip systems and by deformation twinning.

604 The Effect of Initial Tightening Force on the Impact Strength for Bolted Joints

The behavior of bolted joints tightened with steel bolts under the impact tensile load are studied experimentally, changing the mechanical properties classes and length of straightportion of reduced diameter of bolts. The effects of the initial tightening force on the steel bolt strength is clarified through experiment. The result obtained are as follows : (1) As the initial tightening force is increased, the maximum stress and Φ-value (additional force/external impact load) decrease. (2) Without the initial tightening force, the higher the property class, the higher the maximum impact load. (3) Regardless of the property class, increasing the initial tightening force results in lowered impact absorbed energy. (4) Load capacity of the joints tightened in yield point is a little lower than that in elastic region. (5) Permitting the decrease of initial tightening force by 10%, the allowable load is about 85% of the yield strength of the bolt. (6) The allowable load estimated in the joint (load cell) whose stiffness is lower than actual condition is in safety zone.

Fatigue design of an autofrettaged thick-walled pressure vessel using CAE techniques

In order to increase the fatigue life of an autofrettaged thick-walled pressure vessel, computer aided engineering techniques were applied. The fatigue life increase of the external grooved pressure vessel was achieved by relieving the high-stress concentration at the external groove. Shape optimization of the external groove incorporating the finite element stress analysis was performed, resulting in an optimized double grooved pressure vessel which showed a 34% decrease in maximum equivalent stress compared with the conventional single grooved pressure vessel. The fatigue life increase of the double grooved pressure vessel was verified by the simulation fatigue tests using C-shaped specimens, resulting in a 10-times-longer fatigue life. The predicted fatigue life of the pressure vessel using the local strain approach agreed with the simulation fatigue life within a factor of three.

Twyman effect mechanics in grinding and microgrinding

In the Twyman effect (1905), when one side of a thin plate with both sides polished is ground, the plate bends: The ground side becomes convex and is in a state of compressive residual stress, described in terms of force per unit length (Newtons per meter) induced by grinding, the stress (Newtons per square meter) induced by grinding, and the depth of the compressive layer (micrometers). We describe and correlate experiments on optical glasses from the literature in conditions of loose abrasive grinding (lapping at fixed nominal pressure, with abrasives 4-400 μm in size) and deterministic microgrinding experiments (at a fixed infeed rate) conducted at the Center for Optics Manufacturing with bound diamond abrasive tools (with a diamond size of 3-40 μm, embedded in metallic bond) and loose abrasive microgrinding (abrasives of less than 3 μm in size). In brittle grinding conditions, the grinding force and the depth of the compressive layer correlate well with glass mechanical properties describing the fracture process, such as indentation crack size. The maximum surface residual compressive stress decreases, and the depth of the compressive layer increases with increasing abrasive size. In lapping conditions the depth of the abrasive grain penetration into the glass surface scales with the surface roughness, and both are determined primarily by glass hardness and secondarily by Young's modulus for various abrasive sizes and coolants. In the limit of small abrasive size (ductile-mode grinding), the maximum surface compressive stress achieved is near the yield stress of the glass, in agreement with finite-element simulations of indentation in elastic-plastic solids.

Compressive Properties of Yttrium Oxide

Compressive properties of polycrystalline yttrium oxide (Y2O3) were studied by slow‐strain‐rate experiments (ε= 5.7 × 10–6 s−1) between room temperature and 1600°C. It was shown that Y2O3 fails in a brittle manner up to 1000°C, and at 1200°C and above plastic deformation becomes dominant. Plastic deformation of Y2O3 takes place exclusively by dislocation motion. Maximum stress, yield stress, and elastic modulus decrease with increasing temperature, although the decrease at temperatures above 1000°C is much more pronounced.

Dynamic response of cylindrical shells with discontinuity in thickness subjected to axisymmetric load

Abstract Cylindrical shells with discontinuity in the thickness and subjected to harmonic axisymmetric loads have been analyzed. The loadings considered are a uniform internal pressure and a circular ring load at the mid-section. A semi-analytical finite element method is used for the analysis. A thin shell finite element with four degrees of freedom per node is used. Three shell models are analyzed for possible reduction of maximum displacement and maximum stress by choosing the discontinuity at different locations. Numerical results are presented for clamped-clamped end conditions and for various step-ratios in the thickness, for the first three models. The weight of the shell is kept constant for the various step-ratios. It is shown that the maximum displacement and maximum stress decrease for certain types of thickness variations as presented in this paper.

Impulse response of beams with discontinuity in thickness subjected to a point load

Beams with discontinuity in the thickness and subjected to an impulse load at a point are analyzed. A beam element with two degrees of freedom per node is used for the analysis. Three beam models are analyzed for possible reduction of maximum displacement and maximum stress by choosing the discontinuity at different locations. Numerical results are presented for clamped-clamped and simply supported end conditions and for various step-ratios in the thickness. The weight of the beam is kept constant for various step-ratios. It is shown that the maximum displacement and maximum stress decrease for a certain type of thickness variations.

Mechanical properties of Ni2CuSn intermetallic compounds at high temperatures

The present paper reports on the results of the investigation of tensile deformation of Ni2CuSn intermetallic compound samples prepared from as-cast ingot and from hot isostatically pressed material. The yield stress (defined at 0.2% plastic strain) has been investigated as a function of temperature and strain rate in the temperature range from 420 to 870 °C. Both the yield stress and the maximum stress decrease strongly with decreasing temperature. No anomalous behaviour of the stress with temperature is observed. The tensile elongation increases with increasing temperature up to about 750 °C, but decreases beyond this temperature. At lower temperatures, cleavage fracture has been observed, whereas at higher temperatures, ductile fracture mode has been dominant. On the basis of the experimental results, the deformation mechanisms are discussed.

Impulse response of cantilever beams with thickness discontinuity subjected to a point load

Cantilever beams with thickness discontinuity and subjected to an impulse load at a point have been analysed. The beam element with two degrees of freedom per node is used for the analysis. Three beam models are analysed for possible reduction of maximum displacement and maximum stress by choosing the discontinuity at different locations. Numerical results are presented for various step-ratios in the thickness. The weight of the beam is kept constant for various step-ratios. It has been shown that the maximum displacement and maximum stress decrease up to a step-ratio of two for certain type of thickness variations presented in this paper.

Environmental and hold time effects on fatigue of low-tin lead-based solder

The effect of environment on the strain-controlled fatigue resistance of a high-lead-low-tin solder was determined by comparing results in vacuum to those in air (wet and dry) and CO2 (wet and dry). At low strain amplitude, air and CO2 were shown to reduce the cycles to failure defined on the basis of the decrease in maximum cycle stress. The effect increases as the strain amplitude is reduced. Water vapor had little effect. Previously, the Coffin-Manson (C-M) relation was shown to fail for tests in air. The amount of failure is less in vacuum. The main fatigue failure mode is grain-boundary (GB) cracking, and this is accelerated by air or CO2. Auger spectroscopy showed that there is tin buildup near the surface during fatigue in air or CO2. The more rapid GB fracture was attributed to tin oxide (or tin oxide-lead oxide solid solution) buildup in the GB, where diffusion is more rapid.