Influence Of Compressive Stress Research Articles

Simulation of fatigue crack initiation life under compressive loading based on material meso-characteristics

The fatigue problem under compressive loading is common in the key components of aeroengine. Most of the fatigue life prediction methods studied in the past are macroscopic phenomenological methods based on a large amount of experimental data. Due to the difficulty in carrying out the fatigue test under compressive loading, the S-N curve or Manson-Coffin formula commonly used on the fatigue life prediction of material under compressive stress were obtained through fatigue tests under conditions where the average stress was greater than or equal to zero. Although the average stress can be corrected by some formulas, whether the life estimation formulas fitted by those fatigue test data are applicable to the fatigue life analysis with average stress less than zero has not been solved in engineering. And there were few studies on the influence of compressive stress on fatigue life at home and abroad. On the basis of Tanaka-Mura fatigue crack initiation theory, a mesoscopic model suitable for fatigue characteristic analysis under compressive loading was established in this article. The model verified the feasibility in predicting the fatigue initiation life using test data of 7075-T651 aluminum alloy under the compressive fatigue load.

Influence of compressive stress on the magnetic characteristics of grain-oriented material under non-sinusoidal excitation

Electric machines are subjected to mechanical stress during their operation, which significantly affects the magnetic characteristics of the core material. Furthermore, as the converter topologies evolve, the induced harmonic content increases. The analysis of magnetic properties due to both magnetomechanical effects and harmonics is rarely addressed. This work provides a deeper insight into the core loss behavior by analyzing the impact of mechanical stress on the hysteresis characteristics of magnetic materials subjected to non-sinusoidal excitation. A qualitative analysis based on the measured characteristics is presented to study the material behavior under sinusoidal and non-sinusoidal excitations. An analytical approach based on the Lavers’ formula and loss separation theory is presented.

Experimental study and modelling of concrete carbonation under the coupling effect of freeze-thaw cycles and sustained loads

In cold areas, freeze-thaw (F-T) cycles and sustained loads are usually the two main factors affecting the carbonation resistance of concrete, which has been paid more and more attention. In this paper, the effects of F-T cycles and sustained loads on concrete carbonation were studied. An alternating experiment of carbonation and F-T cycles combined with stress was carried out and the carbonation degree was measured by the carbonation depth. Test results show that F-T cycles and sustained loads both have obvious influence on concrete carbonation. F-T cycles and tensile stress could weaken the carbonation resistance of concrete, and the coupling of them has a promotion effect on carbonation. However, since the influence of compressive stress on carbonation is opposite to that of F-T cycles, the coupling effect of the two factors on carbonation depends on which factor plays the leading role. Furthermore, a theoretical carbonation model was established according to the carbonation mechanism and modified to consider the coupling effect of F-T cycles and sustained loads on carbonation. The modified model was proved to have a high accuracy and can be used to predict the carbonation depth of concrete simultaneously subjected to F-T cycles and sustained loads.

Influence of compressive stress on chloride transport in the interfacial zone of precast and cast‐in‐place concrete

AbstractThe large number of interfacial zones of precast and cast‐in‐place concrete weakens the durability and resistance to chloride penetration of fabricated structures. This study investigated the chloride transport behavior in the interfacial zone of precast and cast‐in‐place concrete through long‐term wet–dry cycle experiments. The two influencing factors of compressive stress and distance to the interface were investigated. A chloride concentration test was conducted to investigate the chloride distribution profile, the chloride diffusion coefficient Dapp, and the surface chloride concentration Cs,∆x. The values of Dapp and Cs,∆x correlated with both the location in the interfacial zone and compressive stress, and both dependencies showed complex interactions. All specimens showed different degrees of this interfacial zone effect, which was weakened by compressive stress. Based on the test results, empirical models were developed (by regression) to quantify the dependences of Dapp and Cs,∆x to both compressive stress level and distance to the interface. Applicability of the models was verified.

Influence of compressive stresses on the ultrasonic response of the bone-implant interface

The stress distribution around endosseous implants is an important determinant of the surgical success but it remains difficult to be measured. So far, no method developed to determine the implant stability is sensitive to the loading conditions of the bone-implant interface (BII). The objective of this study is to investigate whether a quantitative ultrasound (QUS) technique may be used to retrieve information on compressive stresses applied to the BII. A dedicated acousto-mechanical device was conceived to compress 18 trabecular bovine bone samples onto coin-shaped implants and to measure the ultrasonic response of the BII during compression. The biomechanical behavior of the trabecular bone samples was modeled as Neo-Hookean. The reflection coefficient of the BII was shown to decrease as a function of the compressive stress during the elastic compression of the trabecular bone samples and during the collapse of the trabecular network, with an average slope of -4.82 GPa-1. Results may be explained by an increase of the bone-implant contact ratio and a change of bone structure occurring during compression. The sensitivity of the QUS response of the BII to compressive stresses opens new paths in the development of patient specific decision support systems allowing surgeons to assess implant stability.

STUDY ON THE INFLUENCE OF COMPRESSIVE STRESS ON THE COMPRESSION SHEAR CRACK PROPAGATION

In this paper, the problem of crack initiation and propagation under compression shear load is investigated experimentally. The influence of far-field compression stress perpendicular to the crack surface on the initiation and propagation of the crack in brittle material is emphasizeded. With the help of the two-axis loading test machine, the two shaft displacements and forces can be adjusted freely during loading. Thus a kind of single-edge symmetric double-crack compression-shear specimen is designed. During the loading, the compression stress stoped as it reaches a series of preset values, while the shear stress increases monotonically till to the crack initiation and propagation. Then the crack initiation and propagation law of compression shear crack under different preset compression stresses can be obtained. It can be find from the test that as the compression stresses relatively smaller, along with the preset compression stress increases, the crack initiation angle increases and the deviation of crack propagation path from the initial crack direction changes severely. As the compression stress reached a definated value, the initiation angle is not changed. It can be find from the test sample that the two crack surfaces are contacted after this definated value of compression stress. The results show that the effect of compression stress on the crack propagation can be divided into two stages according to whether the crack surface contacted or not. Before the crack closed, the influence of compression stress on crack initiation load, crack initiation angle and propagation path increases,when the preset compression stress increases the crack initiation load and the crack initiation angle increase, and the propagation path deviates from the initial crack direction severely. After the crack closed, although the compression stress increases, the crack initiation angle and the critical compression shear stress ratio are keep unchanged. In addition, there existes a certain correspondence between the crack initiation angle and the compression-shear stress ratio at the time of crack initiation. When the ratio of compression-shear stress at the crack initiation increases, the crack initiation angle increases, and vice versa.

Using an Experiment/Simulation-Integrated Approach To Investigate Fracture-Conductivity Evolution and Non-Darcy Flow in a Proppant-Supported Hydraulic Fracture

SummaryOptimizing proppant-pack conductivity in a hydraulic fracture is of critical importance to sustaining effective and economical production of petroleum hydrocarbons. In this study, a hybrid, experiment/simulation-integrated workflow, which combines the discrete element method (DEM) and the lattice Boltzmann (LB) method with laboratory-measured load-embedment correlations, was developed to advance the understanding of fracture-conductivity evolution from partial-monolayer to multilayer concentrations. The influence of compressive stress and proppant-diameter heterogeneity on non-Darcy flow behaviors was also investigated. The DEM method was used to simulate effective-stress increase and the resultant proppant-particle compaction and rearrangement. Proppant-embedment distance was then determined using an empirical correlation obtained by fitting experimental data. The final pore structure of the proppant pack was imported into the LB simulator as interior boundary conditions of fluid-flow modeling in the calculation of time-dependent permeability of the proppant pack. To validate the integrated workflow, proppant-pack conductivity as a function of increasing proppant concentration was simulated and then compared with laboratory data. Good agreement was observed between the workflow-derived and laboratory-measured fracture-conductivity vs. proppant-concentration curves. Furthermore, the role of proppant size, size heterogeneity, and closure pressure on the optimal partial-monolayer proppant concentration was investigated. The optimal partial-monolayer proppant concentration has important engineering implications, because one can achieve a considerable fracture conductivity using a partial-monolayer proppant structure, which has much lower material costs compared with the conventional multilayer proppant structures. To investigate the effect of non-Darcy flow on fracture conductivity, three proppant packs with the same average diameter but different diameter distributions were generated. Specifically, the coefficient of variation (COV) of diameter, defined as the ratio of standard deviation of diameter to mean diameter, was used to characterize the heterogeneity of particle size. The results of this research provide fundamental insights into the multiphysics processes regulating the conductivity evolution of a proppant-supported hydraulic fracture, as well as the role of compressive stress and proppant-size heterogeneity in non-Darcy flows.

Compressive stress-induced autophagy promotes invasion of HeLa cells by facilitating protein turnover in vitro

Metastasis remains the primary cause of cancer mortality. Throughout the process of metastasis, cancer cells experience mechanical forces, which may turn out to be the key towards their migratory, homeostatic and survival characteristics. However, the influence of compressive stress on the underlying mechanism of cancer cell adaptation during metastasis has remained grossly unexplored. In this study, we have investigated whether compressive force induces autophagy in HeLa cells with potential implications in cellular invasiveness. To this end, we have adopted a simple strategy to create the mechanically-compressed tumor microenvironment, in vitro, by applying appropriate compression to agarose-scaffolded HeLa cell-encapsulated alginate beads. Our findings confirm that compression upregulates autophagy, which promotes paxillin turnover and active MMP-2 secretion, leading to enhanced migration of HeLa cells. We further show that autophagy induction by compression is affected by the phosphorylation of p38 MAPKs, a process that is mediated by intact membrane lipid rafts. Identifying the role of such mechanically triggered cellular responses, guiding crucial processes like cell migration, may lead to better understanding of the mechanobiological aspects of metastatic cancer and unveil potential therapeutic targets.

Reinforced, Extruded, Isotropic Magnetic Elastomer Composites: Fabrication and Properties

The study involves the development of isotropic magnetorheological elastomer composites (i-MREs) with improved mechanical properties, their preparations, and properties characterizations. The novelty of the research is the use of extrusion process in the preparation of composites containing two different fillers: carbonyl iron powder (CIP) as magnetic filler and carbon black (FEF, N550) as reinforcing one. So far, the process of extrusion has been used to prepare magnetic composites without filler that improve mechanical properties. It is worth mentioning that the polymer matrix (ethylene-octene copolymer, EOR) offers excellent performance in extrusion applications. In this research, two methods of magnetic composites preparation were reported: traditional, during two-roll mill, and a new one using extrusion process. It was found that the usage of new processing technology allowed forming more homogenous dispersion of particles in elastomer matrix and oriented polymer chains, resulting in an improved rheometric characteristic, increased crosslink density, and decrease of the storage modulus (Payne effect). Based on both static/dynamic mechanical properties and damping properties under the influence of compression stress, the positive influence of extrusion process on material characteristics was confirmed. Moreover, all composites proved very good magnetic properties and resistance to thermooxidative ageing.

The Influence of Compressive Stress on the Load-Bearing Capacity of Masonry Subjected to Vertical Displacements

The paper describes the results of tests of masonry wallets made of solid clay bricks with joints of normal thickness (10 specimens) and filled vertical joints and autoclaved aerated concrete (AAC) blocks with thin joints and unfilled vertical joints (5 specimens). The specimens made of clay bricks were 1290 mm wide, 1415 mm high and 250 mm thick, while the specimens made of AAC blocks had the width of 1250 mm, the height of 1510 mm and the thickness of 240 mm. The tests were carried out in a specially designed steel test stand witch which the masonry specimens were monolithised. The force applied along the vertical edge of the specimens and causing the vertical displacements was carried out by means of hydraulic cylinder. The masonry specimens were tested without participation of vertical compressive stresses perpendicular to the bed joints σc or the tests were carried out after initial compression, which induced stress in the wall with mean values from 0.3 to 1.5 N/mm2 for solid clay brick specimens and 0.9 N/mm2 in walls made of AAC blocks. The compressive loads were implemented using four pairs of tensioned steel tendons equipped with springs to compensate the influence of masonry displacements. The deformation angles of masonry were also investigated. Deformation angles were calculated based on changes in the length of the system of measuring bases placed on both surfaces of the specimens. The compressive stresses σc influenced the values of the mean shear stress τcr,σ (force inducing vertical displacements divided by the area of the vertical cross-section of the specimen) at which the first oblique crack appeared. The τcr,σ stress was always greater than the stress τcr,0 at which the first crack occurred in the specimens tested without compression. The ratio τcr,σ/τcr,0 for solid clay brick specimens ranged from 1.38 to 2.24, depending on the stress value σc and 2.18 for masonry made of AAC blocks. Compressive stresses also influenced the increase of the masonry deformation angles at the moment of the first cracking θcr,σ in relation to the deformation angle θcr,0 of the specimens tested without compression. This effect was proportional to the increase of τcr so that the mean modulus of deformation was about 1630 N/mm2 for clay brick walls. In the case of specimens made of AAC blocks a ratio of stress to angles of deformation Gcr equal to 631 N/mm2 when the tests were not accompanied by compressive stresses (σc = 0) and 461 N/mm2 when σc = 0,90 N/mm2. Similar results were obtained in the case of the effect of the compressive stress σc on the increase of shear stress τu and the accompanying deformation angles λu at the maximum force inducing vertical displacements of masonry specimens obtained in tests.

Experimental study of expanded cork agglomerate blocks – Compressive creep behavior and dynamic performance

The main goal of the present work is to experimentally evaluate the behavior of expanded cork agglomerate blocks subjected to static and dynamic loads. The study focuses on the compressive and creep effects and on the vibration isolation capability.First, compressive creep behavior and deformation recovery capability (after loading) tests were performed on blocks made of expanded cork agglomerate. The dynamic characterization then involved performing transmissibility tests for different static and dynamic loading conditions and evaluating the dynamic transfer stiffness and damping ratio of the blocks. The resulting transmissibility curves indicate how much vibration is transmitted through the isolator to its base at a given frequency. These tests were also performed under different conditions of strain to better understand the effect on the dynamic performance of the material, and to assess whether it might be a limiting factor.The results show that expanded cork agglomerate blocks, especially those with higher mass density, have physical and mechanical properties that provide this material with great potential for withstanding heavy static loads since small compressive creep effects and low permanent deformation was exhibited.The results also indicate that expanded cork agglomerate can be a good option for mitigating vibration. It was found that specimens with lower mass density and larger thickness performed better, with higher vibration isolation and a wider range of frequencies isolated. However, this behavior is limited by the influence of compressive stress on the blocks.

The Influence of Compressive Stresses on the Properties of Inductive Electronics Components

The Influence of Compressive Stresses on the Properties of Inductive Electronics Components

Influence of wheat, rye, and triticale straw on the properties of natural rubber composites

AbstractThe article presents unreported yet in the subject literature results of the research that aim was the examinations of the effect of wheat, rye, and triticale straws obtained from three different fragmentation methods, on the properties of natural rubber composites. Sieve analysis was performed to produce composites with variable filler size fractions. Characterization of mechanical and damping properties, tear strength, hardness, thermo‐oxidative aging performance, and cross‐linking density of obtained biocomposites were reported and studied. It was found that straw fillers with different particle size and shape significantly affected properties of natural rubber composites. The addition of filler (in an appropriate amount and degree of fragmentation) modified natural rubber biocomposites, improving mechanical and physical properties of composites or the ability to damp under the influence of compression stress.

The anhysteretic polarisation of ferroelectrics

Measurement and calculation of anhysteretic curves is a well-established method in the field of magnetic materials and is applied to ferroelectric materials here. The anhysteretic curve is linked to a stable equilibrium state in the domain structure, and ignores dissipative effects related to mechanisms such as domain wall pinning. In this study, an experimental method for characterising the anhysteretic behaviour of ferroelectrics is presented, which is subsequently used to determine the anhysteretic polarisation response of polycrystalline barium titanate and a doped lead zirconate titanate composition at room temperature. Various external parameters, such as electric field, stress, and temperature, can significantly affect ferroelectric behaviour. Ferroelectric hysteresis curves can assess the importance of such effects but cannot distinguish their contribution on the different intrinsic and extrinsic mechanisms involved in ferroelectric behaviour. In this work, the influence of compressive stress on the anhysteretic polarisation is measured and discussed. The comparison of the polarization loop to the anhysteretic curve under compressive stress elucidates the effects on the stable equilibrium domain configuration and dynamic effects associated to dissipation.

Creep of Concrete According to Creep Prediction Models and Own Research

The paper presents the currently used procedures for calculating the deformation of concrete and creep coefficients. Laboratory research was conducted on the creep of concrete. Creep coefficients were calculated on the basis of experimentally obtained data and later compared to the ones acquired by using previously demonstrated procedures. In the case of the sample subjected to the influence of compressive stress and not exceeding the limit of linear creep, the models in Eurocode 2 and fib Model Code 2010 did not correspond to the experimentally obtained data.

Prediction of the critical cutting conditions of serrated chip in high speed machining based on linear stability analysis

A new prediction model was proposed to give the critical cutting condition of serrated chip in high speed machining, including cutting speed, depth of cut, and rake angle. Firstly, a critical criterion of serrated chip in high speed machining was obtained through the linear stability analysis of balance equations of continuum mechanics for primary deformation zone, which considers the influence of compression stress through stress equivalent. Secondly, the model of deformation in the primary deformation zone was proposed to build the corresponding relationships between the cutting conditions and the deformation conditions based on the model of parallel boundary shear zone. Lastly, the critical cutting condition of serrated chip in high speed machining can be predicted by combining the critical criterion and the calculation of deformation conditions in the primary deformation zone. For the validation of model, the critical cutting conditions of serrated chip on AISI 1045 steel were predicted and an orthogonal cutting experiment was performed for comparing with the prediction results. The comparison shows that the prediction results agree well with that of experiment. Therefore, the proposed model is available. This is very useful for the optimization of cutting parameters and precision control of high speed machining.

A dilatometric study on the influence of compressive stresses on the tempering of martensitic AISI 4140 steel - Evidence of transformation induced plasticity during cementite precipitation

Modern surface hardening processes intend among other to induce compressive residual stresses in the near-surface layers of the part. During subsequent tempering, these stresses can affect the phase transformations. Dilatometric tempering experiments starting from martensitic AISI 4140 were performed with a uniaxial compressive stress that simulates the compressive residual stresses mentioned above. An unexpected strain drop, increasing with the applied stress, was measured. It is argued that this effect is due to transformation induced plasticity caused by the Greenwood-Johnson effect. For an applied compressive stress of 358MPa, a strain decrease of 0.6% occurs which means that this has imperatively to be taken into account when tempering a hardened surface with compressive residual stresses.

Natural rubber biocomposites containing corn, barley and wheat straw

The development of high-performance materials made from available and cheap natural resources is increasing worldwide. A new solution – composites of natural rubber, containing barley, corn and wheat straw as biofillers, was reported and researched. The latest developments and trend's exams of the elastomers filled with cereal straw represent a scientific and technological innovation. The use of straw as a filler for elastomer composites bradens the range of functional properties and reduces the costs of production. The biocomposites are more ecofriendly and give the opportunity to increase the possibility of straw management which is a problematic agricultural waste. The rubber mixtures containing lignocellulosic materials demonstrate a favorable characteristic kinetics of crosslinking. The addition of filler, in an appropriate amount, modified natural rubber vulcanizates, improving mechanical and barrier properties of composites and the ability to damp under the influence of compression stress. Dynamic mechanical analysis showed change in the G′ values of the vulcanizates upon addition of straw. That indicates the presence of strongly developed network of fillers into polymer matrix which ensure of reinforcing character. The negative impact of natural fillers on resistance to thermo-oxidative aging was not observed.

The torsional surface wave in a prestressed anisotropic intermediate poroelastic layer of varying heterogeneities

The aim of this paper is to study the behavior of the torsional surface wave in a heterogeneous initially stressed vertical fluid-saturated anisotropic layer sandwiched between inhomogeneous and homogeneous porous half-spaces. It has been considered that the mass density and rigidity of the upper half-space and intermediate layer are space dependent. The proposed model is solved to obtain different dispersion relations for the torsional surface wave in a heterogeneous poroelastic medium lying between two half-spaces. The influence of compressive stress and heterogeneity on torsional surface wave dispersion is shown numerically. It has been observed that heterogeneity, porosity, initial stress of the layer and inhomogeneity of the upper and porosity of lower half-spaces affect the torsional wave speed much. The wave analysis further indicates that the torsional surface waves travel faster in elastic half-spaces in comparison than in the fluid-saturated porous layer.

Influence of Compressive Stress to the Corrosion Rate of Magnesium

Magnesium has made an attention as implant material. Because it is decomposed and absorbed in the body, and its mechanical strength is stronger than that of polymers. It is, however, reported that the corrosion rate increases under the compressive elastic stress. In the other hand, it decreases in the specimen whose surface is applied to compressive residual stress by laser shot peening. This implies that compressive plastic deformation reduces the corrosion rate. In the present paper, the corrosion rate of magnesium that was plastically deformed by uniform high compressive stress was researched. As the result, the corrosion rate decreased as the compressive stress increased.