Increase In Maximum Stress Research Articles

Experimental Study and Damage Model Study of Rock Salt Subjected to Cyclic Loading and Cyclic Creep

Due to the gas injection and production of underground salt caves during the operational phase, rock salt is often subjected to a combined stress of cyclic pressure and constant pressure. In order to investigate the damage evolution of rock salt under different combined stresses, the uniaxial cyclic loading test and cyclic creep test were carried out. The stress‐strain curves, energy characteristics, energy dissipation, and damage of rock salt in the two experiments were analyzed and compared. The test results show that the stress‐strain curves of the two tests presented three stages of “sparse”‐“dense”‐“sparse.” As the maximum stress increases, the stage of “dense” will decrease and the rock salt cycle life will decrease. The relationship between cycle life and Δσ (difference between maximum and minimum stress in the tests) is an exponential function under cyclic loading and a linear relationship under cyclic creep. Based on the experimental data, the energy dissipation of rock salt is analyzed. The damage variables were defined from the perspective of energy dissipation, and the damage evolution of rock salt under two tests was obtained. There are three corresponding stages of energy dissipation and damage: initial, constant speed, and acceleration. The damage model is obtained by inverse functioning the s function, and then the correction coefficient is added to the model to obtain the modified damage model. The modified damage model is compared with the experimental data. The results show that the model can accurately describe the three stages of rock salt damage. The significance of parameters in the modifying damage model is also discussed.

Inversion Method of Initial In Situ Stress Field Based on BP Neural Network and Applying Loads to Unit Body

The initial in situ stress field is the fundamental factor causing the deformation and failure of underground engineering and is an important basis for the feasibility analysis, design, and construction of underground engineering. However, it is difficult to obtain the whole in situ stress field of large‐scale underground engineering in difficult and dangerous areas by field measurement. In view of the fact that the measured in situ stress components (σxx, σyy, σzz, τxy, τxz, τyz) of Sichuan‐Tibet Railway in China are linear with the buried depth, a method is proposed to solve the in situ stress by applying corresponding loads to all unit bodies in the calculation area based on BP neural network and FLAC3D. Through this method, the in situ stress of the tunnel is inverted. The results show that both the maximum principal stress and minimum principal stress increase with the increase of buried depth, and when the tunnel passes through faults or anticlines, the main stress will suddenly drop. Furthermore, compared with the results of the multiple linear regression method, it is found that the proposed method has higher accuracy; especially for the simulation of the maximum horizontal principal stress and vertical stress, the average relative error is reduced by 26.44% and 77.27%, respectively. The research in this paper can provide a new idea for the initial in situ stress inversion of engineering.

Coupled Dynamic Analysis of Liquid Storage Tanks Under Implosion-Generated Overpressure

To deal with the effect of liquid storage on the distribution of implosion, a fluid–solid coupling model is built for the shared nodes of implosion in the liquid storage tank. The displacement compatibility and acceleration and speed coupling are achieved between the implosion field (gas, liquid) and liquid storage tank. First, using this model, the implosion-generated overpressure distribution and structural response under the working condition of half filled tank are obtained. The results show that the overpressure, displacement and stress are high on the shell near the liquid level. Then, the effects of both the TNT equivalent and liquid level on implosion in the liquid storage tank are studied. As the TNT equivalent increases, the maximum overpressure, displacement and stress on the shell near the liquid level increase. Consequently, the maximum overpressure and displacement on the shell near the liquid level exceed those at the roof-to-shell connection of the tank. In contrast, as the liquid level increases, the maximum stress and displacement first increase near the shell. After reaching the peaks near half filled level, they begin to decrease. Only when the liquid reaches a certain level, it can have an attenuating effect on the overpressure at the bottom-to-shell connection. However, if the liquid level continues to rise beyond a certain threshold, the attenuating effect is no longer prominent.

Characterization and physical properties of aluminium foam–polydimethylsiloxane nanocomposite hybrid structures

This article reports on the fabrication and characterisation of hybrid structures prepared by impregnating an open-cell aluminum foam with polydimethylsiloxane (PDMS) or PDMS reinforced with graphene oxide, GO (PDMS nanocomposite). The effect of the PDMS and the GO on the mechanical, thermal, acoustic absorption and fire retardancy properties of the resulting hybrid structures were evaluated and compared to the individual components (PDMS, PDMS nanocomposite, open-cell aluminium foams). Results demonstrate that the use of the PDMS cured at 65 °C, as an void filler of the open-cell aluminium foams, changes mechanical and deformation performance, from a rubbery to brittle behaviour, however attaining a higher level of strength (quasi-static: ~5 MPa; dynamic: >15 MPa) in the resulting hybrid structures. This change is due to the low chain mobility of the polymer and effective adhesion with struts of the open-cell aluminium foams. Furthermore, these hybrid structures are extremely sensitive to strain-rate testing, exhibiting a maximum compressive stress increase of more than 300% and 200%, respectively. The presence of the GO within the PDMS improves significantly the non-flammability of the hybrid structures and increases the sound absorption coefficient.

Effect of Using Tertiary Treated Wastewater from Nablus Wastewater Treatment Plant (NWWTP), On Some Properties of Concrete

This research paper aims at presenting the effect of using tertiary treated wastewater from Nablus Wastewater treatment plant (NWWTP) on some properties of concrete. The research idea have both environmental and economic aspects. The use of tertiary treated wastewater in partial replacement of potable water in concrete mixtures, will save substantial amount of potable water for domestic use. The research variables are water cement ratios (w/c) = 0.5, 0.6 and 0.7, replacement ratios (30%, 60%. and 100%); and curing ages at 7, 14 and 28 days. Different concrete properties were investigated such as compressive strength, natural absorption and workability (Slump). The tests results of concrete cube samples were compared for both types of water, at different replacement ratios and curing ages. The general trend of test results revealed increase in maximum compressive stress of concrete made with w/c=0.5, 0.6, and decrease at w/c=0.7. The recommended replacement ratio of tertiary treated wastewater in concrete mixtures would be 30% to 40%.

Physical ageing of epoxy in a wet environment: Coupling between plasticization and physical ageing

This paper shows how physical ageing and plasticization processes are coupled in an amine-based epoxy. The study combines several ageing conditions including thermal ageing in the dry state (from 40 to 60 °C), ageing in a humid environment (RH 50% and RH 75%) as well as immersion in seawater at several temperatures from 15 to 40 °C. First results are presented to highlight that the two processes (physical ageing and plasticization) both occur when the epoxy is immersed in water. A step-by-step approach is then used to evaluate how the plasticization process induced by the presence of water is affected by physical ageing and vice versa. It appears that the plasticization process, which leads to a large decrease in maximum stress under tensile loading, is not affected by physical ageing of the epoxy. The physical ageing mechanism is not affected by the presence of water in the polymer, i.e. the same increase in maximum tensile stress (26 MPa) is observed in air and in water. However, the kinetic rate of physical ageing is much faster in water due to the plasticization of the polymer. These effects must be considered when accelerated aging methods are applied.

An Enhanced Flow-Thermo-Structural Modeling and Validation for the Integrated Analysis of a Film Cooling Nozzle Guide Vane

The target of this paper is to develop an enhanced flow-thermo-structural (FTS) model with high computational accuracy, to perform the integrated analysis of film cooling nozzle guide vane (NGV). An efficient turbulence model and weak spring approach are utilized in the enhanced FTS model. In respect of the power balance principle of aeroengine rotor shaft and temperature test of a typical combustor, the mean temperature inlet and five normalization temperature curves were confirmed, respectively. The temperature-sensitive paint (TSP) technology was used to verify the numerical simulation. From this study, we find that the predicted temperature caters for the TSP test well, between which the maximum error is less than 6%, and the maximum thermal stress is 758 MPa around the hole edges and the location of stress concentration keeps the consistency with that of the cracks. The maximum thermal stress increases by 10% with the increasing inlet temperature and reduces by about 16% with the shifting of flame peak from the outer to inner hub. The prediction provides general information on the initiation of cracks on a vane segment. The developed enhanced FTS model is validated to be workable and precise in the integrated analysis of film cooling NGV. The efforts of this study provide an integrated analysis approach of film cooling NGV and are promising to provide guidance for the integrated design of film cooling components besides NGV.

Influence of Annealing and Biaxial Expansion on the Properties of Poly(l-Lactic Acid) Medical Tubing.

Poly-l-lactic acid (PLLA) is one of the most common bioabsorbable materials in the medical device field. However, its use in load-bearing applications is limited due to its inferior mechanical properties when compared to many of the competing metal-based permanent and bioabsorbable materials. The objective of this study was to directly compare the influence of both annealing and biaxial expansion processes to improve the material properties of PLLA. Results showed that both annealing and biaxial expansion led to an overall increase in crystallinity and that the crystallites formed during both processes were in the α’ and α forms. 2D-WAXS patterns showed that the preferred orientation of crystallites formed during annealing was parallel to the circumferential direction. While biaxial expansion resulted in orientation in both axial and circumferential directions, with relatively equal sized crystals in both directions, Da (112 Å) and Dc (97 Å). The expansion process had the most profound effect on mechanical performance, with a 65% increase in Young’s modulus, a 45% increase in maximum tensile stress and an 18-fold increase in strain at maximum load. These results indicate that biaxially expanding PLLA at a temperature above Tcc is possible, due to the high strain rates associated with stretch blow moulding.

Novel Insulation Material Based on Basalt Fibres and Silica Aerogels

Basalt fibre reinforced silica aerogel composites with two different fibre lengths and two different fibre volume contents were successfully produced and analysed. After aging and drying of the fibre reinforced aerogel specimens, the geometrical data as well as the weight of each specimen were registered. The microstructure of selected specimens was recorded by tomography. Three-point bending tests were carried out in order to evaluate the effects of the fibrous reinforcement. The shrinkage of the samples was reduced with increasing fibre volume fractions. Specimen with a fibre length of 3.2 mm and a fibre volume fraction of 1.5 % showed the most homogeneous fibre distribution. Specimens with a fibre length of 12.7 mm fibre and a fibre volume fraction of 1.5 % demonstrated the best performance during the three-point bending test, achieving a fivefold increase in the maximum bending stress compared to pure silica aerogel samples with up to 33 kPa.

Analysis of the influence of groundwater and the stress regime on bolt behaviour in underground coal mines

The service failure of rock bolts and cable bolts are frequently reported issues in underground coal mines. Whilst numerous experimental investigations concerned with the service failure of bolts have been conducted, numerical modelling offers an alternative approach in evaluating the factors contributing to service failures of bolts in underground mines. In this study, analysis of the influence of groundwater and tensile stress on bolts in underground coal mines was studied through the numerical modelling of a grouted bolt in the immediate roadway roof. Bolt tensile stress and groundwater dripping rates in the immediate roadway roof were analysed using a package based on finite element method to assess the effect of coal roof thickness and claystone bands, as main contributors of known service failures of bolts in roadways of underground coal mines. Increasing coal roof thickness was found to increase bolt dripping rates. Probable location of stress corrosion cracking (SCC) occurrence was established through examining the shift and increase in maximum bolt tensile stress that was exhibited along the bolt length with increasing coal roof thickness. Claystone bands situated at the top and centre horizon of a grouted bolt produced lower bolt dripping rates compared with scenarios with no claystone bands. Intersecting claystone bands at the centre horizon of a bolt for a fully grouted bolt could increase the likelihood of SCC corrosion and bolt failure by contributing to microbial corrosion processes and grout fracturing by tensile stress. This study improves the understanding the bolt failure associated with the presence of groundwater and changing stress environments, which in turn is imperative in formulating strategies to mitigate support element failures and improve the ground support viability.

Thermal Residual Stress Analysis of Soldering and Lamination Processes for Fabrication of Crystalline Silicon Photovoltaic Modules

In this study, we developed a finite element model to assess the residual stress in the soldering and lamination processes during the fabrication of crystalline silicon (Si) photovoltaic (PV) modules. We found that Si wafers experience maximum thermo-mechanical stress during the soldering process. Then, the Si solar cells experience pressure during the process of lamination of each layer of the PV module. Thus, it is important to decrease the residual stress during soldering of thin Si wafers. The residual stress is affected by the number of busbars, Si wafer thickness, and solder type. Firstly, as the number of busbars increases from two to twelve, the maximum principal stress increases by almost a factor of three (~100 MPa). Such a high first principal stress can cause mechanical failure in some Si wafers. Secondly, thermal warpage increases immediately after the soldering process when the thickness of the Si wafers decreases. Therefore, the number and width of the busbars should be considered in order to avoid mechanical failure. Finally, the residual stress can be reduced by using low melting point solder. The results obtained in this study can be applied to avoid mechanical failure in PV modules employing thin Si wafers.

Unaddressed Cam Deformity Is Associated with Elevated Joint Contact Stress After Periacetabular Osteotomy

Femoral cam deformity is frequently present in patients with acetabular dysplasia. Computational modeling can be used to identify how this deformity affects joint mechanics. Our purpose was to identify the relationship between cam deformity and joint contact stress after periacetabular osteotomy (PAO). We hypothesized that cam deformity is associated with an increase in peak joint contact stress after PAO. This was a retrospective review of patients treated for hip dysplasia with PAO without femoral osteochondroplasty. Patient-specific hip models created from preoperative and postoperative computed tomography (CT) scans were evaluated using discrete element analysis to determine maximum joint contact stress after PAO. Twenty hips with a postoperative increase in maximum contact stress were compared with 20 that demonstrated decreased maximum contact stress. Hips were assessed for cam deformity on cross-sectional imaging. Radiographic measures of acetabular dysplasia before and after PAO were assessed and compared with the change in maximum contact stress after PAO. There was a moderate relationship between the change in maximum contact stress and the α angle (r = 0.31; p = 0.04), and the average α angle in the hips with increased maximum contact stress was significantly different from that in the hips with decreased joint contact stress (51° ± 11.4° versus 42° ± 5.1°; p = 0.04). All 6 hips with an α angle of >60° demonstrated increased joint contact stress. Cam deformity is common in patients with hip dysplasia. In our study, α angles of >60° were associated with increased postoperative joint contact stress. The α angle should be assessed preoperatively, and deformity should be addressed for optimal joint mechanics after PAO. A reduction in joint contact stress is a proposed mechanism for the increased joint longevity following periacetabular osteotomy for hip dysplasia. Impingement from abnormal femoral offset negatively impacts clinical outcome, but this finding has not been evaluated from a biomechanical perspective previously and a threshold for performing femoral osteochondroplasty has not been established previously. This study provides biomechanical evidence supporting surgical management of femoral cam deformity for an α angle of >60°.

Mechanical behaviour of coarse grains/fines mixture under monotonic and cyclic loadings

Abstract Micro-ballast/fines mixtures were tested at various contents of coarse grains in triaxial cells under monotonic and cyclic loadings. X-ray µCT scans were undertaken to visualise the coarse grains distributions in the compacted samples. Results show that inclusion of coarse grains has significant effect on the mechanical behaviour of micro-ballast/fines mixture. While the volumetric content of coarse grains f v increases, the cohesion decreases, the friction angle increases, the dilatancy becomes more pronounced, the maximum deviator stress increases, the permanent deformation decreases, the resilient modulus increases and the damping ratio decreases. There is a characteristic volumetric content of coarse grains f v - c h a , that defines two zones: when f v f v - c h a , the mechanical behaviour is governed by the fines proportion. On the contrary, when f v > f v - c h a , the mechanical behaviour is controlled by the coarse grains proposition. This is totally supported by the X-ray µCT scans which revealed that when f v varies from 0% to 10% (below f v - c h a ), the fine particles constitute the skeleton of the sample, with coarse grains drowned in the matrix of fines. When f v increases to 20% (still below f v - c h a ), the connections between coarse grains start to develop. As f v > 35% (beyond f v - c h a ), almost all coarse grains are connected to form a skeleton of grain-grain contacts.

Joint contact stresses calculated for acetabular dysplasia patients using discrete element analysis are significantly influenced by the applied gait pattern

Gait modifications in acetabular dysplasia patients may influence cartilage contact stress patterns within the hip joint, with serious implications for clinical outcomes and the risk of developing osteoarthritis. The objective of this study was to understand how the gait pattern used to load computational models of dysplastic hips influences computed joint mechanics. Three-dimensional pre- and post-operative hip models of thirty patients previously treated for hip dysplasia with periacetabular osteotomy (PAO) were developed for performing discrete element analysis (DEA). Using DEA, contact stress patterns were calculated for each pre- and post-operative hip model when loaded with an instrumented total hip, a dysplastic, a matched control, and a normal gait pattern. DEA models loaded with the dysplastic and matched control gait patterns had significantly higher (p = 0.012 and p < 0.001) average pre-operative maximum contact stress than models loaded with the normal gait. Models loaded with the dysplastic and matched control gait patterns had nearly significantly higher (p = 0.051) and significantly higher (p = 0.008) average pre-operative contact stress, respectively, than models loaded with the instrumented hip gait. Following PAO, the average maximum contact stress for DEA models loaded with the dysplastic and matched control patterns decreased, which was significantly different (p < 0.001) from observed increases in maximum contact stress calculated when utilizing the instrumented hip and normal gait patterns. The correlation between change in DEA-computed maximum contact stress and the change in radiographic measurements of lateral center-edge angle were greatest (R2 = 0.330) when utilizing the dysplastic gait pattern. These results indicate that utilizing a dysplastic gait pattern to load DEA models may be a crucial element to capturing contact stress patterns most representative of this patient population.

Pitch bearing/raceway fretting: Influence of contact angle

In this paper, a three-dimensional numerical simulation (using ABAQUS) of the radial and tangential wear between a ball bearing and a raceway is presented. The aim was to study the influence of the contact angle between ball and raceway on the fretting. A range of contact angles was studied with critical parameters such as contact stress, relative slip, plastic deformation, and contact state. The model was validated against experimental data. The results show that with an increase in the contact angle, the area of maximum stress increases, the bearing capacity of the raceway decreases, and the maximum radial stress moves from the sub-surface to the raceway surface. The raceway surface is shown to be prone to peeling and wear, which reduces the service life of the raceway.

Effects of stress on failure behaviour of shallow-marine muds from the northern Gulf of Mexico

Abstract Direct simple shear experiments on mud samples from 0 to 15 mbsf (metres below seafloor) in the Ursa Basin (northern Gulf of Mexico) document that stress level impacts shear strength and pore pressure during failure. As burial depth increased (from 7.35 to 13.28 mbsf), cohesion decreased (from 12.3 to 6.5 kPa) and the internal friction angle increased (from 18° to 21°). For a specimen from 11.75 mbsf, an increase in maximum consolidation stress (from 45 to 179 kPa) resulted in an increase in the shear-induced pore pressure (from 29 to 150 kPa); however, the normalized peak shear stress decreased (from 0.37 to 0.25). Our results document that consolidation at shallow depths induces a positive feedback on pore-pressure genesis. For resedimented samples, which lack a stress history, cohesion was 3.6 kPa and the internal friction angle was 24°. As the maximum consolidation stress increased (from 40 to 254 kPa) on resedimented samples, the shear-induced pore pressure increased (from 22 to 203 kPa), whereas the normalized peak shear stress decreased (from 0.32 to 0.25). Our experiments showed that resedimented samples have similar strength and failure behaviour to intact samples. By constraining pore pressure, strength and initial stress state, we gain a better insight into slope-failure dynamics. Therefore, our experiments provide constraints on strength and shear-induced pore pressure at the onset of shallow failure that could be included in slope-failure and hazard models.

Mechanical behaviour of a pipe impacted by an object, based on numerical simulation

DAMAGE TO A PIPE squeezed by other object are one of the key damages for oil and gas pipelines. Mechanical behaviour of a pipeline section in a deformed state was investigated by numerical simulation. Effects of initial dent depth and pipe diameter / wall thickness ratio on the mechanical behaviour of the dented pipe were studied. The results show that the squeezing force, high stress area, and the maximum stress increase in the loading process. In the unloading process, there is a high probability for recovery of the pipeline section elastic strain to initial values. Cross-section of the middle plane is flatted. The deformation of the pipe in the vertical plane is V-shaped. In the first stage, the maximum equivalent plastic strain appears in the centre part of the pipe. There are two maximum equivalent plastic strain areas with the increasing of the squeezing object’s displacement. In the unloading process, the equivalent plastic strain increases. With the increasing of the initial indentation depth, the resilient rate of the pipe dent decreases, but the maximum equivalent plastic strain increases. With the increasing of pipe diameter / wall thickness ratio, the resilient rate increases but the maximum equivalent plastic strain decreases.

High-cycle fatigue behavior of low-C medium-Mn high strength steel with austenite-martensite submicron-sized lath-like structure

In this study, the high-cycle fatigue behavior of low-C medium-Mn high strength steel was studied at stress ratio R (σmin/σmax) = − 1 and 0.1. Excellent fatigue performance with push-pull fatigue limit strength (σ−1) and pull-pull fatigue limit strength (σ0.1) after 107 cycles of 450 MPa and 683 MPa was obtained. The fatigue ratio (σ−1/Rm, σ0.1/Rm) was 0.54 and 0.82, respectively. Two types of failure modes were observed, surface-induced failure mode and internal inclusion-induced failure mode. The retained austenite (RA) transformation ratio of fracture surface increased from ~ 30% to ~ 63% with increase in maximum stress (σmax) from 470 MPa to 550 MPa. The higher mechanical driving force contributed to the total driving force for martensite transformation, and higher damage accumulation in terms of cyclic plasticity. The high density of high misorientation boundaries between tempered martensite effectively prevented the propagation of fatigue crack, and enhanced the fatigue strength. The experimental steel with excellent fatigue property was mainly attributed to the transformation-induced plasticity (TRIP) effect of metastable RA in the small plastic deformation zone, which relaxed the local stress concentration, absorbed the strain energy, delayed the crack initiation and suppressed its propagation.

Effect of off-plane bifurcation angles of primary bronchi on expiratory flows in the human trachea

BackgroundThe human airway is exposed to the development of diverse flow patterns based on differences in its morphological/geometrical parameters across individuals. Although effects of the asymmetry between the right and left main bronchi on airway flows have been investigated in the past, there exists a paucity in terms of studies that focus on the role of stronger physiological asymmetric features, such as off-plane bifurcation angles of primary bronchi, in expiratory flows. MethodComputational fluid dynamic techniques have been used to demonstrate presence of Dean-type secondary flows and vortices in the bifurcation region. Formation of a distinctive pattern was observed corresponding to an increase in the off-plane branching angle. An experiment involving 3D printed airways and smoke was also performed to visualize flow patterns and verify simulation results. ResultsGood agreement was observed between computational and experimental results. Furthermore, it was revealed that the predicted wall shear stress distribution demonstrated significant changes (with a maximum shear stress increase of 30.7%) compared to conventional airway models that adopt symmetric bifurcation angles. The overall flow demonstrated a swerving motion, which was characterized by tracking the vortex cores (maximum accumulated radial movement of 72.6°) when they ascended towards the trachea inlet in off-plane airway models. ConclusionsIt was confirmed that off-plane bifurcations in human trachea significantly alter the flow characteristics in expiratory flows. It is expected that the results of this study will provide useful information regarding increasingly advanced patient-specific treatments for respiratory diseases in the trachea.

Hardened raceway calculation analysis of a three-row roller slewing bearing

Three-row roller slewing bearings are large and often exposed to quite complex loads. The raceway surface is hardened to improve its carrying capacity. An inadequate hardened raceway depth can cause the raceway to be crushed. In contrast, an excessively large hardened raceway depth can increase the overall vibration, processing difficulty, and cost. Thus, it is critical to determine the optimal hardening depth. We propose a quick method to analyze this depth. The use of non-linear springs instead of a solid roller provides the maximum contact load between the roller and raceway according to the actual load conditions. A finite element model for the local roller and raceway contact is established. The depth thickness under the raceway is divided into a hardened layer, a transition layer, and a core layer. Each layer has distinct elastic–plastic material parameters. The results of a roller and raceway compression experiment validate the roller and raceway finite element model. The accuracy of the raceway as described by the model with different layers is verified by an indentation test of heat-treated 42CrMo. The results show the following: 1) both the value and depth position of the maximum stress increase under normal loads, and 2) the choice of algorithm has a strong influence on the calculated value of the fatigue life.