Strain Behavior Research Articles

Effects of particle size and particle concentration of poly (ethylene‐co‐methacrylic acid) on properties of epoxy resin

AbstractSelf‐healing polymers have been developed to improve durability and reduce costs associated with maintenance during service. The addition of thermoplastics to thermosets to produce mendable polymers appears as a promising self‐healing technique. In this study, poly (ethylene‐co‐methacrylic acid) (EMAA) was added to epoxy resin and the effects of EMAA addition on epoxy properties were evaluated. Specimens with two different contents of thermoplastic and particles sizes were manufactured. A two‐level full factorial experimental design was used to evaluate the effect of particle size and particle content on properties of epoxy modified with addition of EMAA. Tensile tests and dynamic mechanical analysis (DMA) were used and the evaluated responses were tensile strength, modulus of elasticity, and glass transition temperature (Tg). X‐ray computed tomography (XCT) was used to investigate particle size and concentration after manufacturing. It was found that the particle concentration has greater effects on stress–strain behavior of epoxy while Tg was not significantly affected by neither of the analyzed entrance variables.

A non-linear stress–strain relationship for soil and rock

While many employ a hyperbolic stress–strain relationship for soils, it is known that such a relationship is accurate over the small-strain range as encountered in earthquake and soil dynamics problems. For large strains, a relationship with different input parameters is needed, as is required for finite-element analyses of large-deformation behaviour. These separate characterisations do not carry over into the other application. Here, a proposed power relationship is presented that was developed to characterise the triaxial test stress–strain behaviour of cohesionless material from lubricated or ‘frictionless’ cap and base tests (144 tests) covering a range in the natural variation in particle size, particle shape and surface roughness, over low to high confining pressure. This relationship covers the strain range from 10−6 to soil failure. To date, it has been successfully used in laterally loaded pile response characterisation (the strain wedge model) and shallow-foundation load–settlement–bearing capacity response. Most recently, it has been extended to assess the behaviour of rock-like material (caliche). The relationship and its comparison with the hyperbolic relationship for large strain and the shear modulus reduction curve for seismic behaviour are presented.

Enhancement of hardness and tribological properties of AISI 321 by cathodic cage plasma nitriding at various pulsed duty cycle

AISI 321, an austenitic stainless steel, has high corrosion and temperature resistance, making it useful for aerospace and chemical processing. Cathodic cage plasma nitriding (CCPN) is a versatile technique that enhances material surface characteristics. This study aims to investigate the effect of the pulsed duty cycle from 10 % to 60 % on microhardness and tribological properties through CCPN treatment. The X-ray diffraction (XRD) analysis indicates a noticeable shift in the γ-phase towards the lower 2θ angle originating from the expanded austenite phase γN by the lattice expansion at the lowest duty cycle. Nitriding at the lowest duty cycle reduced the average crystallite size from 68 nm (untreated) to 4.5 nm, while increasing the duty cycle led to a decrease in micro-strain. The surface microhardness of the sample that underwent the lowest duty cycle improved to 1288 HV0.01 compared to the untreated sample (210 HV0.01). Moreover, the lowest wear rate is observed for the sample nitrided at a low-duty cycle, which agrees with hardness and strain behavior. The results show that the variable pulsed duty in CCPN can improve the surface hardness and tribological properties of AISI 321, particularly at low-duty cycles.

The Role of Vesicular Glutamate Transporter Type 3 in Social Behavior, with a Focus on the Median Raphe Region.

Social behavior is important for our well-being, and its dysfunctions impact several pathological conditions. Although the involvement of glutamate is undeniable, the relevance of vesicular glutamate transporter type 3 (VGluT3), a specific vesicular transporter, in the control of social behavior is not sufficiently explored. Since midbrain median raphe region (MRR) is implicated in social behavior and the nucleus contains high amount of VGluT3+ neurons, we compared the behavior of male VGluT3 knock-out (KO) and VGluT3-Cre mice, the latter after chemogenetic MRR-VGluT3 manipulation. Appropriate control groups were included. Behavioral test battery was used for social behavior (sociability, social discrimination, social interaction, resident intruder test) and possible confounding factors (open field, elevated plus maze, Y-maze tests). Neuronal activation was studied by c-Fos immunohistochemistry. Human relevance was confirmed by VGluT3 gene expression in relevant human brainstem areas. VGluT3 KO mice exhibited increased anxiety, social interest, but also aggressive behavior in anxiogenic environment and impaired social memory. For KO animals, social interaction induced lower cell activation in the anterior cingulate, infralimbic cortex, and medial septum. In turn, excitation of MRR-VGluT3+ neurons was anxiolytic. Inhibition increased social interest 24 h later but decreased mobility and social behavior in aggressive context. Chemogenetic activation increased the number of c-Fos+ neurons only in the MRR. We confirmed the increased anxiety-like behavior and impaired memory of VGluT3 KO strain and revealed increased, but inadequate, social behavior. MRR-VGluT3 neurons regulated mobility and social and anxiety-like behavior in a context-dependent manner. The presence of VGluT3 mRNA on corresponding human brain areas suggests clinical relevance.

Tensile Forces Behavior on Longitudinal Reinforcement and CFRP Strips on Circular Hollow Reinforced Concrete Columns

Abstract Currently, there is not much research on strengthening structural elements with hollows. This manuscript presents the test results from twelve circular reinforced concrete column specimens strengthened with CFRP strips. This study focuses on the strain behavior of longitudinal reinforcement and CFRP strips due to high shear force intensity. Hollows in the cross-section are used to see the effect of voids on the column strain distribution. Nine specimens have a hollow cross-section with hollow diameters of 1.5", 2.5", and 3.5" for each of the three specimens. Meanwhile, the other three specimens have a solid crosssection. All specimens do not use stirrups to determine the contribution of concrete and CFRP strips to resist shear. Strain gauges are placed in certain positions to read the strain on the longitudinal reinforcement and CFRP strips. The test results are in the form of tensile forces and are then analyzed to obtain the movement pattern of tensile forces in the longitudinal reinforcement and CFRP strips. Numerical analysis using a fiber element model is used to obtain the strain in each reinforcement layer. The numerical analysis results were then compared with the test results and showed close results. Then, an equation for calculating the tensile force in CFRP strips is proposed. The proposed equation approximates the test results with an accuracy level of 90%.

Modeling Nonlinear Stress–Strain Behavior of 6000 Series Aluminum Alloys under Cyclic Loading

Modeling Nonlinear Stress–Strain Behavior of 6000 Series Aluminum Alloys under Cyclic Loading

Reinforcement mechanism and the stress-strain behaviors of geocells made by non-woven geotextile

Geocell is one of the most widely employed geosynthetics for reinforcing soil beds across diverse applications, including base layer pavement and various structures such as embankments, foundations, and retaining walls. Its reinforcement mechanisms encompass both vertical and lateral cellular confinement, enhancing load distribution. Geocells are commonly made from polymer networks like high-density polyethylene (HDPE), non-woven geotextiles, and geogrids. Each type of geocell offers special advantages and effects on the reinforcement mechanism for the soil bed, dependent on material stiffness and effective opening size. This paper aims to assess both the reinforcement mechanism and stress–strain behavior of geocells (made by non-woven geotextile). To this end, three series of plate-loading tests were conducted on reinforced sand beds. The reinforcement configurations included single cells as well as multi-cells arranged in predetermined patterns. The experiments enabled us to determine bearing capacity, vertical surface displacement and axial strain of cell wall for different pocket sizes and numbers of cells. The results suggest that cells with pocket sizes matching the diameter of the loading plate exhibit superior performance. Furthermore, a comparative analysis between performance of single cells and multi-cells revealed that incorporating adjacent cells, particularly for geocells with smaller pocket sizes, significantly mitigates loading plate settlement. In addition, the results showed that the axial strain and deformation applied on non-woven geotextiles were more pronounced for smaller pocket sizes than for cells with larger pocket sizes.

Deformation of rectangular orthotropic laminate resting on thin elastic foundation with nonlinear change of displacements over thickness under edge loading

Deformation of rectangular orthotropic laminate resting on a thin elastic orthotropic foundation with fully fixed bottom plane is studied in this paper. The laminate is subjected to an in-plane uniaxial load uniformly distributed over one of its edges. Models of joint deformation of the laminate and foundation are created based on the equations of plane elasticity for an orthotropic body. The applicability of such equations is justified by the uniformity of edge loading. A laminate model allows for the transverse shear strain, whereas a model created for the foundation considers a nonlinear character of variation of the transverse and axial displacements. A governing system of differential equationsmodelling the joined deformation of the laminate and foundation is derived using static and kinematic contact conditions. The corresponding boundary value problem is solved using the sweep method. Based on this solution, effects of laminate and foundation thicknesses, and elasticity characteristics on the stress–strain state of the jointed structure are investigated. The model created and the method of its analysis enable the strong oscillating behaviour of stresses and strains to be studied. The results obtained can be utilized for verification of solutions of similar problems found by other numerical methods, including finite-element analyses.

Optical detection of passive thermal lattice deformation of monolayer WS2 in van der Waals heterostructures of WS2/h-BN

Van der Waals heterostructures (vdWHs) of the constituent two-dimensional (2D) layered materials are quickly emerging as functional structures for diverse novel electronic and optoelectronic devices. To further explore the device applications of the vdWHs, an open question, which is whether the lattice of atomic thin active layer follows the deformation of its neighboring thick layers in a vdWH, needs to be clarified. Herein, the thermal deformation of WS2 monolayers in vdWHs with and without hexagonal boron nitride (h-BN) layers on SiO2/Si substrates is investigated with combined optical spectroscopies of photoluminescence (PL) and Raman scattering. With a developed strategy extracting the pure strain-induced effects from the temperature-dependent PL and Raman scattering spectroscopic results, the relative deformations of the WS2 monolayers and the h-BN layers with respect to the substrate have been identified. Both the Raman and PL results consistently reveal that the lattice variation of the WS2 monolayers passively match the deformation of the h-BN layers, and the WS2 monolayer on the SiO2/Si substrate exhibits the largest strain. These findings have not only demonstrated the passive behavior of the thermal strain of 2D semiconductor monolayers in vdWHs heterostructures, but also paved a way to tailor the thermal strain via designing and constructing vdWHs.

The effect of bedding thickness on interlocking block pavement performance

ABSTRACT An interlocking block pavement (IBP) comprises discrete blocks, joints, bedding sand, and base and subbase layers. The thickness of the bedding sand layer gives significant impact on IBP performance. However, previous laboratory model tests have often overlooked the geotechnical properties of paving materials and the deformation characteristics of the sublayers, leading to conflicting recommendations regarding appropriate thickness. This study performed laboratory tests on IBP models with varying bedding thicknesses (30, 50, and 80 mm), considering the geotechnical properties (relative density, shear strength, and stress–strain behaviour) of the paving materials. In addition, a novel two-dimensional (2D) model chamber with a transparent wall was designed for particle image velocimetry (PIV) analysis to assess the overall deformation of the sublayers. The test results demonstrated that a bedding thickness of 50 mm exhibited higher load-dispersion ability, allowing the blocks to settle and rotate appropriately and achieving a full interlocking effect. Consequently, the deflection in the sublayer was distributed over a wide area at shallow depths. However, a bedding thickness of 30 mm provided a better performance in terms of resistance to deflection, imposing a higher stress on the base layer.

Enhancing geomechanical characteristics of calcium sulfoaluminate (CSA) cement-treated soil under low confining pressures

This study examines the efficacy of employing calcium sulfoaluminate (CSA) cement, an environmentally friendly binder, for enhancing the geomechanical characteristics of sand, particularly under low confining pressure conditions. A series of triaxial consolidated drained tests were performed on sand samples treated with varying content (5, 7, and 10%) of CSA cement and 10% ordinary Portland cement (OPC) under various low confining pressures (50, 100, 200, and 400 kPa). The test findings demonstrated the importance of cement content and confining pressure on the mode of failure, stress–strain and volumetric behavior, failure characteristics, and shear strength parameters of the treated quartz sand. After a curing period of 14 days, samples treated with 10% CSA cement exhibited a remarkable 212% increase in peak deviator stress and an 89% reduction in axial strain at failure, indicating higher initial stiffness compared to untreated samples under a 400 kPa confining pressure. Furthermore, the samples treated with 10% CSA exhibited higher peak deviator stress, initial stiffness, and strength development compared to those treated with 10% OPC. The scanning electron microscopy analysis provides insights into particle breakage and bond degradation processes, which increase with confining pressure in CSA-treated samples. Also, the mode of failure analysis reveals a transition from ductile to slightly brittle behavior with increasing cement content. Notably, the geomechanical properties of the treated material emphasized the significant impact of CSA cement on soil improvement. Thus offering a sustainable alternative for soil improvement in construction projects.

Spatial reconstruction, microstructure-based modeling of compressive deformation behavior, and prediction of mechanical properties in lightweight Al-based entropy alloys

Lightweight Al-based entropy alloys are newly emerged materials with promising potential for structural applications; however, their modeling and strengthening prediction require further exploration. In this study, the spatial distributions of various phases in three Al-based entropy alloys were investigated. A closely interconnected intermetallic compound (IC) network comprising Al2Cu and Al45Cr7 phases was identified. Finite element (FE) modeling was conducted based on the reconstructed three-dimensional microstructure to simulate compressive deformation behavior. The IC network served as the main stress bearer during deformation. Thin sections in the Al2Cu network were the weak sites where stress concentration and damage first occurred. However, the breakage of this limited region contributes to relatively coordinated deformation and extended plasticity. The breakage of large particles accounts for the final alloy failure. The results of the FE model were compared with the experimentally measured stress–strain behavior and mechanical properties, showing very good agreement. Given the non-uniform distribution of strain and stress during deformation, a strengthening model, merging the Voigt and Reuss models, was also developed to predict the mechanical properties of Al-based entropy alloys with the aim of facilitating Al-based entropy alloy development.

Prediction of Stress–Strain Behavior of PET FRP-Confined Concrete Using Machine Learning Models

Prediction of Stress–Strain Behavior of PET FRP-Confined Concrete Using Machine Learning Models

Structural behavior of one-way slabs reinforced by a combination of GFRP and steel bars: An experimental and numerical investigation

Abstract Glass- fiber-reinforced polymer (GFRP) offers a significant alternative to steel in reinforced concrete, with superior corrosion and fire resistance. Though less ductile and more brittle in stress–strain behavior than steel, it is very helpful to combine GFRP with steel reinforcement that improves the structural behavior. This research investigates the flexural characteristics of a one-way slab reinforced by a combination of GFRP and steel reinforcement. Three identical concrete slabs ((1500 × 550 × 120) mm and 43 MPa) were tested under static load with GFRP replacement ratios of (0, 20, and 40)%. The experimental data were utilized to verify a numerical model. The experimental outcomes indicated a substantial impact of the GFRP replacement ratio on the failure mode. The failure mode was flexural, flexural-shear, and shear regarding the reference slab, 20%, and 40% replacement, respectively. GFRP replacement influenced ductility and ultimate load by (9.13 and 10.7)% and (−21 and 5.0)% for replacement ratio (20 and 40)%, respectively. Based on the numerical analysis, the parametric study (considerably affected the structural response. Failure mode changed to flexural, and shear-flexural concerning (20 and 40)%, respectively. The optimum load was characterized at 40%, while max toughness and ductility were achieved at 20%.

Integrating Dendrogeomorphology into Stress–Strain Numerical Models: An Opportunity to Monitor Slope Dynamic

Monitoring systems are recognized worldwide as fundamental tools for landslide risk management. However, monitoring can be difficult when dealing with large slopes in forested areas. In these situations, dendrogeomorphology can offer a low-cost and low-impact alternative for providing distributed information with an annual temporal resolution. The present study is a first attempt to integrate dendrometric and dendrogeomorphic data into a numerical finite difference model, in order to simulate the stress–strain behavior of the tree-slope system. By using a parametrical approach, the capability of the numerical model to effectively reproduce the tree stem anomalies (i.e., tilting angle, J-shaped feature, and internal stresses causing tree-ring growth anomalies such as eccentric growth and reaction wood) was verified, and the target parameters for the model calibration were identified based on a sensitivity analysis, which emphasized the relevance of the wood deformability; moreover, the interpretation of results allowed to point out different peculiarities (in terms of type of deformation, falling direction, and distribution of internal stresses) for different slope conditions (kinematics and depth of the failure surface) and different zones of the landslide (head scarp, main body, and toe). Afterwards, the modeling approach was applied to the Val Roncaglia landslide (Northen Italy), which involves a complex roto-translational kinematics, characterized by multiple sliding surfaces. The simulated stem anomalies showed good agreement with the ones arising from onsite dendrometric surveys, and they confirmed the conceptual model of the landslide, enabling the planning of further specific investigations. Moreover, the capability of the model in reproducing the tilting angle of trees, if correlated to their eccentricity, could provide a quite long time series (over more than 50–60 years) of the landslide reactivation and allow the use of dendrochronological data for the model calibration, thereby enhancing slope dynamic monitoring and landslide risk management.

Influence of weak interlayer thickness on mechanical response and failure behavior of rock under true triaxial stress condition

In this study, we meticulously investigate the influence of the thickness of weak interlayer on mechanical response and failure behavior of rock mass near the free surface of tunnel, with the aid of a true triaxial test system. We simulated the true triaxial stress condition of rock mass containing weak interlayer proximate to the excavation boundary, where one face remains free, while others are subjected to loading stress and increasing tangential stress. The experimental results reveal a distinct change in the fracture morphology near the free surface of rock mass as the thickness of weak interlayer increases, concomitant with a gradual decrease in the fractal dimension. With the increase of the thickness of weak interlayer, the failure characteristics of rock mass change from a “binary” to a “unitary” feature, i.e. mixed tension-shear failure near the free surface and shear failure far away from the free surface changes to mixed tension-shear failure that only occurs near the free surface. Moreover, an inverse relationship is observed between the bearing capacity of the rock mass and the thickness of weak interlayer. Conversely, the peak strain in the tangential stress direction increases with the increase of the thickness of weak interlayer, illustrating that the slip shear strain of rock block positioned above the weak interlayer is gradually formed, and governs the strain behavior of rock mass in the tangential stress direction with the increases of the thickness of weak interlayer. By employing the finite-discrete element method (FDEM), we replicated the failure process of surrounding rocks containing weak interlayers near the free surface of tunnel, demonstrating considerable congruity with our physical test results. In light of the failure characteristics of surrounding rocks containing weak interlayers, we advocated a localized area priority reinforcement support strategy, prioritizing regions with weak interlayers. Numerical simulations verified the effectiveness of this approach in controlling fracture proliferation in surrounding rocks and inhibiting the splitting failure of surrounding rocks containing weak interlayers near the free surface of tunnel.

The mediating effect of health behaviors on the association between job strain and mental health outcome: a national survey of police officers.

Police officers often face emotionally challenging interpersonal situations and numerous studies have demonstrated that policing is a stressful occupation. A study revealed a significant positive correlation between emotional demands among police officers and emotional dissonance, as well as burnout. Health-promoting behaviors can contribute to better overall health outcomes and reduce the risk of developing health problems, but there is limited research evaluating the association of job strain and health behaviors with mental health outcomes in police officers. The objective of this study was to assess the job strain associated with mental health mediated by health behaviors in Taiwanese police officers. This was a cross-sectional quantitative study conducted in Oct 2016. A total of 41,871 police officers (response rate was 79.7%) participated questionnaire that consisted of demographic information, job characteristics, health behaviors, and mental component summary (MCS) scores of the Short-Form Health Survey. Independent t-tests and one-way analysis of variance (One-way ANOVA) were conducted to assess the differences in mean MCS scores across various demographics, health behavior, and job characteristics. Multivariate regression analyses were used to assess the relationship between job strain and health behaviors with mental health outcomes. MCS scores were associated with job characteristics and health behaviors among police officers except for gender. After adjusting for covariates, multivariate analysis indicated that police officers with high job demands and high job strain index exhibited poor MCS scores. Job strain was significantly associated with MCS mediated by health behaviors (consumption of fruits and vegetables, and physical activity) in Taiwanese police officers. Since regular physical activity and increased vegetable and fruit consumption might alleviate the effects of job strain on mental health status, it is recommended that institutional policies be established to promote health-enhancing behaviors among police officers.

The Effect of Stiffness on Friction, Surface Strain and Contact Area of a Sliding Finger Pad Simulant

This study investigates the frictional and surface strain behaviour of silicone hemispherical finger pad simulants with different stiffness during tribological interactions with a smooth glass plate. A novel contact area and strain measurement method employing a digital image correlation technique was employed to give new understanding of the pad behaviour during sliding. The frictional behaviour of the sliding finger pad simulant is dominated by the adhesion mechanism, with a small overall contribution from deformation, as suggested by the high principal strains at the edge of the contact area. The strain behaviour is also influenced by the magnitude of the normal force and the stiffness of the samples.

A Comprehensive Review of the Evaluation and Application of Engineering Properties of Expansive Soil Based on Piezocone Penetration Test (CPTU)

Expansive soil presents several challenges in civil and geotechnical engineering because of its distinctive physical and mechanical properties, including considerable volumetric fluctuations, non-linear stress–strain behaviour, and high permeability. Owing to soil disturbances and sample size limitations during sampling, important parameters such as the expansive soil expansion force, compressive strength, and shear strength obtained through indoor experiments often cannot accurately reflect the values in situ. In this regard, in situ piezocone penetration testing has the advantages of small disturbances and high efficiency and has been widely used in subways, bridges, highways, and other engineering projects. This paper comprehensively summarizes the research progress of in situ testing technology in the evaluation and application of engineering properties of expansive soils in China and internationally. First, a detailed analysis of the basic theories and physical mechanisms of various in situ testing methods is provided, focusing on their applicability and accuracy in expansive soils. Second, examples of the application of in situ testing technology in expansive soil engineering are summarized. Finally, predictive models and methods based on in situ testing data, especially those that introduce cutting-edge models such as machine learning and advanced data analysis techniques, are discussed.

Prediction of mechanical properties and fatigue life of nanosilver slurry in chip interconnection

This article investigates the failure mode and mechanism of copper pillar solder joints in temperature cycling experiments, focusing on a Cu/nano Ag/Cu solder joint structure. The hot pressing bonding condition at 300 °C with insulation for 10 s is chosen for the experiments. Based on the life test results, the thermal cycling fatigue life of the nanosilver solder joint is determined to be 2050 cycles. To gain further insights, finite element software ANSYS is employed to simulate nanosilver solder joints in flip chips, revealing the stress–strain distribution within the solder joints. The simulation utilizes the Anand viscoplastic constitutive model for the solder joint, providing a reasonable representation of the stress–strain behavior under thermal cycling load. Notably, the simulation highlights that the maximum stress and strain occur in the contact area between the solder joint and the copper column. To enhance accuracy, the calculation equation is refined using relevant experience, resulting in a prediction of the thermal fatigue life of nanosilver solder joints. This prediction aligns closely with the experimental results. The research outcomes not only contribute valuable insights into the behavior of nanosilver solder but also serve as a reference for its application in electronic packaging.