Ratio Of Compressive Stress Research Articles

Yield asymmetry design of magnesium alloys by integrated computational materials engineering

Deformation asymmetry of magnesium alloys is an important factor on machine design in the automobile industry. Represented by the ratio of compressive yield stress (CYS) against tensile yield stress (TYS), deformation asymmetry is strongly related to texture and grain size. A polycrystalline viscoplasticity model, modified intermediate ϕ-model, is used to predict the deformation behavior of magnesium alloys with different grain sizes. Validated with experimental results, integrated computational materials engineering is applied to find out the route in achieving desired asymmetry via thermomechanical processing. For example, CYS/TYS in rolled texture is smaller than 1 under different loading directions. In other textures, such as extruded texture, CYS/TYS is large along the normal direction. Starting from rolled texture, asymmetry will increase to close to 1 along the rolling direction after being compressed to a strain of 0.2. Our modified ϕ-model also shows that grain refinement increases CYS/TYS. Along with texture control, grain refinement also can optimize the yield asymmetry. After the grain size decreases to a critical value, CYS/TYS reaches to 1 because CYS increases much faster than TYS. By tailoring the microstructure using texture control and grain refinement, it is achievable to optimize yield asymmetry in wrought magnesium alloys.

Comparative Study on Compression Deformation Behaviors of Cast and Extruded AZ31 Alloys

Compression properties, microstructure evolution and deformation behaviors of cast and extruded AZ31 alloys are investigated. The results show that compressive yield stress, ultimate strength and ultimate compression ratio between extruded and cast AZ31 alloy are quite different. The yielding pattern of as-cast AZ31 alloy is continuous, and the yield pattern of extruded AZ31 alloy demonstrate an obvious yielding plateau mode. The angle between the fractures and specimens axis of as-cast and extruded AZ31 alloy is about 45°. A mass of reliefs and damage can be found on the specimen surface of as-cast AZ31 alloy and the twinning is main deformation sign in as-cast AZ31 alloy as seen a rough surface. The slip activity might be a predominant deformation mechanism in extruded AZ31 alloy judged by smooth surface after fracture.

Structural and mechanical properties of the coral and nacre and the potentiality of their use as bone substitutes

The main objective of this work is to develop resistant compact material samples with different porosities from coral and nacre adapted to the filling of bone cavities. The characterization of materials was conducted using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS) and laser granulometry. The micro-hardness and the influence of porosity on the mechanical behavior of these biomaterials under compression as well as three-points bending tests were also assessed. Both materials showed similar particles size ranging from 50 to 100μm in diameter, distributed according to the Gauss curve. The modal particle size, the median D50 and D90–D10 are the most important parameters which allow for the distinction between coral and nacre samples. The two biomaterials showed a micro hardness (138–167HV for coral and 261–340HV for nacre) higher than that of bovine bones (55–70HV). The maximum compression stresses were 32.82MPa for coral and 37.06MPa for nacre at 50% of porosity. S–N curve with ASME format is constructed to predict the fatigue life extended from 101 to 106 cycles, which reveals an endurance limit at a compression stress ratio of about 10.

Microstructure and tensile properties of consolidated magnesium chips

In this study tensile properties of consolidated magnesium chips obtained from solid state re-cycling (SSR) has been examined and correlated with the microstructure. Chips machined from as-cast billet of pure magnesium were consolidated through SSR technique, comprising of compaction at ambient conditions followed by hot extrusion at four different temperatures viz., 250, 300, 350 and 400°C. The extruded rods were characterized for microstructure and their room temperature tensile properties. Both ultimate tensile strength and 0.2% proof stress of these consolidated materials are higher by 15–35% compared to reference material (as cast and extruded). Further these materials obey Hall–Petch relation with respect to strength dependence of grain size. Strain hardening behavior, measured in terms of hardening exponent, hardening capacity and hardening rate was found to be distinctly different in chip consolidated material compared to reference material. Strength asymmetry, measured as a ratio of compressive proof stress to tensile proof stress was higher in chip consolidated material.

압축응력이 인가된 콘크리트의 열화제어를 위한 표면도막공법의 효과

For cracked concrete, it is obvious that cracks should be preferential channel for the penetration of aggressive substances such as chloride ions according to the previous researches. In order to extend the lifetime of cracked concrete, critical issues in the performance of the concrete is the risk of chloride-induced corrosion. Even though crack width can be reduced due to the high reinforcement ratio, the question is to which extend these cracks may jeopardize the durability of cracked concrete. If the size of crack is small, surface treatment system can be considered as one of the best options to extend the service life of concrete structures exposed to marine environment simply in terms of cost effectiveness versus durability performance. Thus, it should be decided to undertake an experimental study on the effect of surface coating system, which can be able to seal the concrete and the cracks to aggressive substances-induced corrosion in particular. In this study, it is excuted to examine the effect of surfaced treated systems on chloride penetration and carbonation through compressive stress induced cracks. Experimental results have showed conclusively that critical stress linked with deterioration, should be existed in compressive stress ratio 50 ~ 70% for chloride penetration and 70 ~ 80% for carbonation, respectively. When the critical stress is exceeded in concrete, a comparatively large deterioration was measured where the critical stress in concrete, the increase in the mass transportation is marginal in spite of the large increase in micro-cracks. As for the effect of surface coating system on crack-sealing, it can be seen conclusively that cracks can be healed.

The assessment of residual stresses in welded high strength steel box sections

Much work on the investigation of the magnitude and distribution of residual stresses in mild carbon steel sections have been made previously. However, limited efforts have been put on residual stress measurements of high strength steel sections. The differences of stress–strain curves and high-temperature material properties between the high strength steel and mild carbon steel demands a necessary study of the residual stresses in high strength steel welded sections. In the present study, three box columns fabricated from Q460 steel plates of 11mm in thickness with different details were used for the examination. Both sectioning and hole-drilling methods are adopted for the measurement. The measured residual stress distributions of three different box sections are presented, and the corresponding simplified residual stress pattern is proposed. By comparing with the residual stress patterns for mild carbon steel, it is found that the box section fabricated from HSS plates has the lower compressive residual stress ratio. The differences in the measurement by using sectioning and hole-drilling methods are also compared.

Biomechanical study on the edge shapes for penetrating keratoplasty

A parametric study to investigate the compressive and the shear stress distributions for various edge shapes created during penetrating keratoplasty (PK) using femtosecond laser is reported. The finite element analysis has been implemented using ABAQUS to study the cornea with various edge shapes, namely the standard edge shape, the zigzag edge shape, the top hat edge shape and the mushroom edge shape for PK. The ratio of maximum compressive stress to maximum shear stress is used as the main factor to assess the relative merits of wound healing rate for different edge shapes. For the typical values of tissue mechanical properties, the zigzag edge shape has the highest ratio of maximum compressive stress to maximum shear stress (11.1 in the xy-direction and 3.7 in the yz-direction), followed by the mushroom edge shape (7.7 in the xy-direction and 3.2 in the yz-direction). The ratios for the top hat and the standard edge shapes are even lower in both directions. A sensitivity analysis of the model has been done to demonstrate that the zigzag edge shape always results in the highest ratios of stresses regardless of the difference in the tissue mechanical properties. The zigzag edge shape also gives the lowest dioptric power D = 45.4. The present results imply that the zigzag edge shape provides the best wound healing rate and optical outcome among the four edge shapes models for PK.

Experimental Study of Wet-Screened Aggregate Concrete under Biaxial Compression after Freeze-Thaw Cycles

Using the static and dynamic triaxial experimental machine, experimental study of the strength of wet-screened aggregate concrete are carried out under biaxial compression stress ratios, 0.25, 0.5, 0.75 and 1 after 0, 50, 100, 150, 200, 250, 300 cycles of freeze-thaw. The change of surface of wet-screened aggregate concrete specimens after different cycles of freeze-thaw are observed and described. The failure characteristic of specimens and the direction of the cracks are also observed. Based on the test data, the influence of freeze-thaw cycles and compressive stress ratio on the ultimate compressive strength and corresponding stress-strain relationship is analyzed respectively. The relationships between the ultimate compressive strength and freeze-thaw cycles, the stress ratios are given, respectively. On this basis, the unified failure criterion with consideration of the influence of freeze-thaw cycles and stress ratio is proposed. It can serve as a reference for the maintenance, design and the life prediction of ocean structures, hydraulic structures, marine structures and offshore platform in cold regions.

Low-Cycle Fatigue Deformation Behavior and Evaluation of Fatigue Life on Extruded Magnesium Alloys

To evaluate fatigue deformation behavior and fatigue life of extruded magnesium alloy, total strain-controlled and stress-controlled low-cycle fatigue test of three extruded magnesium alloys, AZ31, AZ61 and AZ80, were performed in ambient atmosphere at room temperature using smooth round bar specimen. Mean tensile stress during total strain-controlled fatigue process and mean compressive strain during stress-controlled fatigue process appeared due to asymmetry of yield stress between tension and compression. The values of mean stress and mean strain appeared on three alloys were associated with the ratio of compressive yield stress to tensile one, which resulted in mechanical twinning in the compressive phase. Fatigue criteria proposed previously considering the mean stress effect were evaluated in terms of fatigue life predictions based on the experimental results. Also, an energy-based model taken into account of plastic and elastic energy density was discussed to predict the fatigue lives obtained from total strain- and stress-controlled fatigue experiments.

Low-Cycle Fatigue Properties of Extruded AZ31 Magnesium Alloy

Fully reversed tension-compression low-cycle fatigue tests controlled by both of total strain and stress were conducted on extruded AZ31 magnesium alloy using smooth round bar specimens in ambient atmosphere at room temperature. The stress-strain hysteresis loops exhibited a characteristic asymmetric shape with a positive mean stress during total strain-controlled fatigue cycle, in comparison with those with a compressive mean strain under stress-controlled fatigue test. The mean stress was associated with the ratio of compressive yield stress and tensile one in the material, which resulted in mechanical twinning in the compressive phase. The fatigue lives obtained from both controlled experiments were nicely described by the Coffin-Manson relationship. From the plastic strain range-life curves, fatigue life under total strain-controlled fatigue test was shorter than that under stress-controlled one because of an effect of tensile mean stress. Fatigue criteria considering the mean stress effect previously proposed were evaluated in terms of fatigue life predictions based on the experimental results. Also, an energy-based model taken into account of plastic and elastic energy density was discussed to predict the fatigue lives obtained from total strain- and stress-controlled fatigue experiments.

Fatigue Failure and Thermal Spalling Tests to Evaluate Dynamic Fatigue Fracture of MgO–C Bricks

The relationship between compressive stress and loading cycles in MgO–C bricks with various carbon contents was investigated at room temperature and high temperature. The relationship between fatigue failure and thermal spalling was investigated by estimating a characteristic material constant, which represents the degree of sensitivity of crack growth, in terms of fracture mechanics. The relationship between the ratio of compressive stress for compressive strength and loading cycles in MgO–C bricks is not affected by the temperature of the atmosphere. At the same acting stress ratio, fatigue fracture life decreased as the carbon content in the MgO–C bricks decreased. In the thermal spalling test, the number of heating cycles at which small cracks and large cracks were generated decreased as the carbon content decreased. In the fatigue failure test, the ratio of the dynamic elastic modulus to the initial elastic modulus decreased gradually. This ratio also showed a gradual decrease in the thermal spalling test as the number of heating cycles increased. A characteristic material constant was obtained and compared based on the results of a fracture mechanics discussion. The characteristic material constant obtained from the fatigue failure test was substantially the same as that obtained from the thermal spalling test. From this, a relationship in which crack growth behavior leading to fatigue failure is equivalent to that of thermal spalling in MgO–C brick was recognized.

Mechanical behaviour of air-entrained concrete

Experimental investigation on the mechanical behaviour of air-entrained concrete under uniaxial compression, uniaxial tension, biaxial compression, biaxial tension–compression (T–C) and triaxial tension–compression–compression (T–C–C) loading conditions was carried out. The biaxial compression stress ratios α2=σ2/σ3=0·25, 0·5, 0·75, 1·0, biaxial tension–compression stress ratios α1 = σ1/σ3 = −0·05, −0·1, −0·3, −0·5 and triaxial tension–compression–compression stress ratios α=σ1:σ2:σ3= − 0·25:0·25: 1·0, − 0·25: 0·5:1·0, − 0·25:0·75:1·0, − 0·25:1·0:1·0 were selected as the major test variables. The failure characteristic of specimens and the direction of the crack are observed. Based on the test data, the biaxial ultimate strength envelopes and the failure criterion under triaxial T–C–C in principal stress space were proposed. The test results indicated that the strength of air-entrained concrete specimens under biaxial compression is higher than that under uniaxial compression and the maximum increase of ultimate strength occurred at a biaxial compression stress ratio of 0·5. The relationship between the ultimate compressive strength and stress ratio was given. It provides the experimental and theory foundations for strength analysis of air-entrained concrete structures.

Behavior of air-entrained concrete under the compression with constant confined stress after freeze–thaw cycles

Properties of air-entrained concrete under compressive loads with constant confined stress after 0, 100, 200, 300 and 400 cycles of freeze–thaw were studied. The failure characteristic of specimens and the direction of the crack are observed. Based on the test data, the influence of freeze–thaw cycles and lateral compressive stress ratio on the ultimate compressive strength is analyzed, respectively. The relationships between the ultimate compressive strength and freeze–thaw cycles, lateral compressive stress ratio are given, respectively. The unified failure criterion with consideration of the influence of freeze–thaw cycles and stress ratio is proposed. It provides the experimental and theory foundations for strength analysis of air-entrained concrete structures subject to complex loads in cold environment.

Development of Magnesium Alloys with High Performance

In Mg-Al-Zn and Mg-Al-Mn alloys containing 2.0~6.0mass%Al and 0~1.5mass%Zn, grain refinement in the as-rolled (F) specimens containing large amount of Al and Zn are achieved by both dynamic recrystallization and dynamic precipitation during hot rolling and leads to high strength and high ductility at room temperature. At high temperatures, the tensile strength of the investigated alloys is almost the same, while the elongation of the F-specimens increases with increasing Al and Zn contents, leading to 150% in Mg-4.5%Al-1.5%Zn alloy. High Al and Zn contents alloys significantly accumulate large working strain in grain interiors, and involve large amounts of high angle grain boundaries and fine spherical precipitates, which can become the nucleation sites for recrystallization. Therefore, dynamic recrystallization in such alloys occurs at small strain region during tensile test. This dynamic recrystallization causes reduction of flow stress and large elongation by grain boundary sliding at high temperatures. Furthermore, .fine recrystallized grains contributes to deformation in normal direction, resulting in isotropic deformation behavior. Authors attempt to improve proof stress and its anisotropic property of Mg-Al-Zn wrought alloys by grain size and precipitates controls utilizing dynamic recrystallization and dynamic precipitation during hot extrusion. In the alloy specimens extruded at lower temperatures increasing Al and Zn contents enhance dynamic recrystallization and dynamic precipitation, resulting in grain refinement and large amount of Mg17Al12 precipitates. As a result, the extruded Mg-9%Al-1%Zn alloy specimen shows high tensile strength of 370MPa, 0.2% tensile proof stress of 240MPa and moderate elongation of 20%, which are almost same as standard values of tensile properties of T5-treated 6N01 Al extruded alloy. Furthermore, a ratio of compressive proof stress to tensile proof stress of the as-extruded specimen improves up to a higher ratio of 0.9 than that of Mg-3%Al-1%Zn alloy specimen with no precipitation, 0.5, due to prevention of tensile twin, which easily occurs during compressive deformation even under a low applied stress perpendicular to the extrusion direction, by dynamic precipitation of Mg17Al12 phase.

Seismic behavior of RC columns with circular, square and diamond sections

A numerical solution procedure based on the finite grid element method and an iterative procedure is developed with considerations of two different nonlinear stress–strain relations for confined core concrete by stirrups and for unconfined cover concrete. The lateral load–displacement curves can be obtained numerically, where the effects of geometrical nonlinearity, plastic hinge zone, bond slip of reinforcement and shear deformation are taken into account. Then 14 large-scale column specimens, including six circular columns, four square columns and four diamond columns, are designed and investigated experimentally under low frequency cyclic lateral load with very high constant axial load level. The comparison of the numerical results with the experimental results is undertaken and shows a good agreement. Finally, some recommendations on the limit values for the axial compressive stress ratio of RC columns with circular, square and diamond sections are made.

Analysis of the Stress State at the Cogging Joint in Timber Structures

This paper presents a finite-element-based analysis of carpentry joints between structural timber members. Currently, the design of these joints is conducted by using simplifying assumptions of the stress distribution and of the distribution of forces on the contacting surfaces, and neglects the effect of contact friction between surfaces. Such unrealistic assumptions affect the computation of stresses and the tensile and compressive stress ratio of the joint. This study presents a more realistic approach by conducting a numerical simulation of the behaviour of carpentry joints, which enables optimisation in the geometric definition of this type of joints. Finite element analysis reveals the importance of the effect of friction between the contacting surfaces. In addition, the angle between the members affects the distribution of stresses along the contacting surfaces.

Experimental study of strength and deformation of plain concrete under biaxial compression after freezing and thawing cycles

This study attempts to generate information about the strength and deformation behavior of plain concrete under biaxial compression after 0, 25, 50 and 75 cycles of freezing and thawing. Concrete cubes were tested under biaxial compressive stresses. Five principal compression stress ratios and four different cycles of freeze–thaw were the main variables. Static compressive strengths, stress–strain relationships and failure modes were examined. Failure modes of specimens are also described. The experimental results showed that the biaxial compressive strength of plain concrete decreased as the freeze–thaw cycles were repeated. The influence of freeze–thaw cycles and the stress ratio on the biaxial strength, the strain corresponding to peak stress and the elastic modulus after freeze–thaw cycles was also analyzed. The formula of the biaxial compressive strength in principal stress space is proposed.

Fabrication of iron aluminum alloy/steel laminate by clad rolling

Laminates of an iron-aluminum alloy (20Al) and three types of steel—chromium molybdenum (CrMo), high carbon (FeCMn), and precipitation hardening steel with niobium carbide (FeCNb)—were fabricated at 600 °C and 1000 °C by clad rolling based on the compression stress ratio of 20Al to steel. The laminates fabricated at 600 °C exhibit a deformation microstructure with partial recrystallization, while those at 1000 °C reveal a refined microstructure. The 20Al layer of all the laminates exhibit a {001}〈110〉 texture, and the intensity of the texture increases with a decrease in the fabrication temperature and an increase in the reduction. The bending deformability of a laminate increases with a decrease in the compression stress ratio and by a reduction in the intensity of the {001}〈110〉 texture. The clad plate is further rolled at room temperature to a thickness of approximately 150 µm, which enables winding without damage. It is concluded that a high-strength steel at high temperatures and a high Al content in the Fe-Al alloy is beneficial for the fabrication of deformable laminates.

Microcracks in New England granitoids: A record of thermoelastic relaxation during exhumation of intracontinental crust

The upper intracontinental crust carries an excess horizontal compression, a remnant stress that arises because exhumation-related thermoelastic relaxation of deeper horizontal stress lags behind the reduction in overburden stress. This remnant stress appears in Earth stress data as an interchange in orientation of vertical σ 2 and horizontal σ 3 so that the ratio of least compressive horizontal stress ( S hmin ) to vertical compressive stress ( S v ) is >1 in much of the top 2 km of intracontinental crust. In theory, rocks exhumed from beneath 2 km should carry some record of this stress interchange, and this record is found in the orientation and density of healed, filled, and open micro-cracks in exhumed New England granitoids. Fluid inclusion planes (FIP) of older, healed microcracks are the best developed in a vertical orientation, and younger filled and open microcracks are best developed in the horizontal plane. Lateral unloading during initial isobaric cooling from the solidus of laterally constrained granite allows early microcrack growth once horizontal tension on the microscopic scale develops in response to vertical compression from the overburden load. During exhumation, further relaxation of lateral compressive stress takes place by a combination of decompression and cooling so that Δ S hmin /Δ S v

コンクリートの遷移温度クリープ性状に関する研究 : 温度80℃以下における遷移温度クリープを含む線膨張係数

It is important to grasp the thermal properties of concrete including creep of concrete for preventing cracks of reinforced concrete members subjected to repeated thermal loads. Some experiments were conducted using cocrete specimens under constant compressive stress subjected to temperatures up to about 80℃ at slow heating and/or cooling rate to evaluate thermal strain including transient thermal creep. From the experiments, the following conclusions were derived: 1.The influence of transient thermal creep was most remarkable at the very first-time heating for the concrete, though the influence at the repeated heating and cooling phase of concrete was little. 2.A new coefficient of thermal expansion including transient thermal creep can be formulated by both the heating rate and the applied compressive stress ratio of concrete.