Mechanical Behavior Research Articles

Effect of moisture content on the rockburst intensity of sandstones

Rockburst is a common geological hazard in deep underground engineering, and it often occurs in strata consisting of brittle rocks. In this study, the moisture content effect on the rockburst intensity of sandstones is systematically studied. A series of triaxial unloading compression tests along with the acoustic emission monitoring are performed for sandstone specimens with different moisture content levels. The mechanical properties, failure characteristics, and dilatancy behaviors of sandstone specimens are then properly compared. Comparative results reveal that the triaxial compressive strength and total strain energy of the saturated specimen decrease by about 30% and 35%, respectively, as compared to those of the dry specimen. Moreover, the magnitude of elastic strain energy tends to decrease with the increasing water content. The effect of moisture content on the rockburst intensity of sandstones is, therefore, significant. Besides, it is also found that the onset of dilatancy is generally unaffected by the water content, whereas the extent of dilatancy significantly decreases with the increasing water content. Numerical simulations for a tunnel excavation model confirm that injecting water into the surrounding rock is an effective way of reducing the rockburst intensity during tunnel excavations. These results have a guiding significance for the prevention and control of rockbursts in underground engineering.

Compressive mechanical properties of styrene-butadiene rubber under medium-low strain rates: Experiments and modeling

Styrene-butadiene rubber (SBR) is widely employed as a cushioning material in engineering applications to resist impact loadings due to its excellent mechanical properties and energy absorption capacity. This paper aims to investigate the compressive mechanical properties and constitutive model of SBR under medium–low strain rates both experimentally and theoretically. Firstly, quasi-static and dynamic compression tests of SBR were carried out under the strain rate up to 220 s−1 using an electronic universal testing machine and a drop-weight machine, respectively. Subsequently, the effect of loading rate on mechanical properties, strain rate sensitivity and energy absorption capacity was examined. The results indicate that SBR exhibits visco-hyperelastic characteristics with reversible compression deformation and strain rate dependency, ie., the yield stress, flow stress and dynamic increase factor (DIF) increase approximately exponentially with increasing logarithmic strain rate. In addition, the SBR exhibits excellent energy absorption capacity during compression, especially under higher strain rates and larger strain levels. Finally, a visco-hyperelastic constitutive model was proposed by replacing the nonlinear spring with a hyperelastic element in Zhu-Wang-Tang (ZWT) viscoelastic constitutive model to describe the nonlinear mechanical behaviors in SBR, and an acceptable agreement between experimental results and model predictions were observed. The findings of this research can provide a valuable guide for designing and optimizing the impact resistance of SBR structures.

Experimental and numerical study on mechanical behavior of 3D printed adhesive joints with polycarbonate substrates

AbstractAdhesive joints play a crucial role in enhancing the structural integrity and performance of 3D printed parts. The purpose of this study is to investigate the failure load and behavior of polycarbonate (PC) single lap joints (SLJs) produced by fused deposition modeling (FDM) using experimental and finite element analysis (FEA) methods. The FEA of joints presents a new approach by integrating PC substrates with Hill yield criterion, transversely isotropic material and adhesive layer with cohesive zone modeling (CZM). The study focused on the effect of printing angles (0°, 45°, and 90°) and overlap lengths (12.5 and 25 mm) on the performance of SLJs. The influence of 3D printing parameters on the mechanical behavior of PC joints was investigated by tensile testing of SLJs. The experimental failure load was 1586 N for a 12.5 mm joint at 90° and 4115 N for a 25.4 mm joint at 0°. Comparison of the experimental and FEA failure loads of the joints showed maximum and minimum differences of 11.98% and 1.34%, respectively. This result showed that the proposed model is applicable for determining the joint strength as a function of the printing angle and monitoring the joint damage behavior.

Theoretical Modeling and Mechanical Characterization at Increasing Temperatures under Compressive Loads of Al Core and Honeycomb Sandwich

This work investigates the mechanical behavior under out-of-plane compression of the Al core and honeycomb sandwich at increasing temperatures of up to 300 °C. After the first introductive theoretical modeling on room-temperature compressive behavior, the experimental results at increasing temperatures up to 300 °C are presented and discussed. The analysis of the results shows that peak stress, plateau stress, and specific absorbed energy gradually decrease as the temperature increases. The final densification occurs always at the same strain level (around 75%). Sandwich honeycomb test temperatures have been limited to 200 °C for bonding problems of the skin to the sandwich due to the glue. The experimental and modeling results agree well at room temperature as well at increasing temperatures. The results can provide useful information to choose base materials for greater energy absorption at increasing temperatures.

Influence of thickness and restorative system on the mechanical behavior of CAD/CAM minimally invasive occlusal veneers - in vitro study.

The aim of this study was to evaluate the physical-mechanical behavior of the occlusal veneers when subjected to thermomechanical cycling. Sixty specimens were divided into 04 groups (n=15 per group), according with the different restorative materials and thicknesses: material - lithium dissilicate LD (IPS e.max CAD, Ivoclar Vivadent) and nano- ceramic-resins NCR (ESPE Lava Ultimate, 3M); thickness - 0.6 and 1.2mm. The occlusal veneers were bonded over human flattened fresh extracted molars with dual-polymerizing luting agent (Variolink N, Ivoclar Vivadent and RelyX Ultimate 3M) using the respective adhesive system following the selective-etch technique (self-etch in dentin and total etch in enamel). The resin cement was light cured for 40 seconds each face, using a LED light cure equipment (BlueStar II, Microdont, 1100 mW/cm2). The response variables consisted of veneer survival rates (crack formation, catastrophic cracks and debonding) when subjected to thermal cycling from 5° to 55° C and simultaneous mechanical cycling performed at load intensities of 100, 200, 300, 400 and 450N for 20,000 cycles each. Data were submitted to the Kruskall Wallis test and Pairwise Comparison, adopting a significance level of 5%. NCRs presented a lower incidence of failures (p<0.05) when compared to LD. According to thickness factor, 1.2mm thick occlusal veneers withstand higher cycling loads. NCR occlusal veneers with 1.2mm thickness presented superior physical-mechanical behavior than lithium disilicate and 0.6mm restorations.

Enhancing strength-ductility properties of immiscible W–Cu composite by creating low-energy phase interfaces

The immiscible bimetallic composites play an important role in civilian industries and aerospace fields owing to their integrated mechanical and physical properties. However, metallic composites of immiscible constituents suffer from one critical drawback of weak interface bonding, which makes the composites particularly vulnerable at elevated service temperatures. Here we proposed a novel strategy to resolve the challenge by creating low-energy phase interfaces in a typical immiscible bimetallic W–Cu composite. This was achieved by in-situ reactions of WO3 and CuO with WC, which acts in a dual function as the reducing agent for the reactions and an interface forming agent. The sintered W-WC-Cu composite possessed a significant number of low-energy WC/W and WC/Cu interfaces and exhibited a compressive strength of 609 MPa and a compressive ductility of 22.6 % at 600 °C, which ranks among the highest in similar composites. The characteristics of WC/W and WC/Cu interfaces and their effects on the mechanical behavior of the composite were demonstrated by the timely and atomic-resolved high-temperature mechanical investigations. The introduced stable interfaces were also found to induce [1‾ 11]BCC→ [011]FCC phase transformation of W as another mechanism of plastic deformation in addition to dislocation activities in W and Cu. This study provides a new approach to greatly enhance the mechanical properties of the immiscible metallic composites.

Exploring gradual material rigidity degradation effects on the nonlinear coupled axial-transversal nonlinear response of a capacitive micro-beam

The accumulation of damage in materials due to crack propagation can lead them to unpredicted failures. This phenomenon is particularly relevant in materials science, engineering, and other fields where structures or components are subjected to repeated loading, cyclic stresses, or environmental factors. In this paper, the mechanical behavior of a microelectromechanical system subjected to cyclic loads has been modeled, when the stiffness of the material gradually is decreased. As a case study the dynamic response of a micro-beam to DC bias voltage as a static load and AC harmonic voltage as a cyclic load has been studied. The nonlinear coupled equations have been formed and converted to time-dependent ones using a spatial discretization method. Due to long-term integration over time, to achieve more accurate results besides direct 4th order Runge-Kutta integration method, a temporal decomposition method has been used to solve the coupled nonlinear ordinary differential equations. To realize this method, a temporal decomposed solution based on the physical nature of the problem is presented in the form of slow-growing terms and fast-altering harmonic terms with gradually-growing amplitudes. To find the coefficient of these terms a least square method has been utilized to minimize a cost function in a given dynamic time-interval, where the independency of the results to this interval has been assessed. Also, the nonlinear frequency behavior of the proposed model has been studied when the system has suffered various damages. Due to considering gradual rigidity degradation of the material interesting dynamic responses have been observed, that can help to expand the insight in the design of structures.

Thermodynamic Prediction and Experimental Verification of Transformation‐Induced Plasticity/Twinning‐Induced Plasticity Effects in Advanced Low‐C High‐Mn Steel at Different Deformation Temperatures

The effectiveness of transformation‐induced plasticity (TRIP)/twinning‐induced plasticity (TWIP) effects in Fe–0.06C–26Mn–3Si–3Al advanced ferrous alloy is analyzed over a wide temperature range of −40 to 200 °C. The specific deformation mechanisms in the steel are experimentally investigated and predicted using thermodynamic calculations of stacking fault energy (SFE). These predictions were correlated with the microstructure of the steel and its mechanical behavior. The study finds that applied thermodynamic models effectively predict the occurrence of TRIP/TWIP effects at different deformation temperatures, aligning well with experimental observations in terms of ε/α′ martensite formation, indicative of the TRIP mechanism. Some discrepancies in SFE results are observed at Mn contents significantly higher or lower than the nominal composition of steel.

Experimental Evaluation of Mechanical Properties, Micro Structure and Post-Fire Strength of Fiber Reinforced Geopolymer Concrete

Geopolymer mixtures offer an enhanced alternative to implement an eco-friendly solution in construction industry. These mixtures exhibit similar or better mechanical and structural properties in comprising of cement and can use recycling and by-product materials. Against this background, an eco-friendly advantageous were achieved from the engineers and researchers by using waste materials to replace cement and attention to reduce CO2 emission during its procedure. This study attempted to evaluate compressive and tensile strength, micro structure and post-fire characteristic of the geopolymer mixtures. For this aim, the geopolymer mixtures were exposed to elevated temperature between 200, 500 and 800 0C. Then, the post-fire and mechanical behaviour were investigated. The proposed research supported the slight decrease in the GPC's compressive stress by fibres, and the 1.25% PP fibres displayed the least performance, indicating nearly 13% decrease than the unreinforced mixtures. As exhibited by the post-fire behaviour of mixtures, the GPC's compressive strength increased first for all mixes but in the range of 400 - 800°C it decreased at a higher rate because of the geopolymer matrix-related dehydration. Besides, fiber melting under high temperatures and the thermal reaction procedure related to free water evaporation reduce the mechanical properties under temperatures ranging from 400°C to 800°C. DOI: https://doi.org/10.52783/pst.349

Enhanced microstructure and mechanical properties of ZrN-reinforced AlSi10Mg aluminum matrix composite

Aluminum matrix composites (AMCs), incorporating Zirconium Nitride (ZrN) as reinforcing additives, demonstrate immense promise for applications in aerospace, automotive, and power generation due to their unique combination of low density, superior mechanical properties, and excellent thermal/electrical conductivity. This study explores the influence of ZrN reinforcement on the microstructure and mechanical properties of AlSi10Mg metal-matrix composites. Utilizing high-energy ball milling (HEBM) and spark-plasma sintering (SPS), ZrN/AlSi10Mg composites were synthesized, achieving nearly full density with uniform ZrN distribution, while phase and chemical transformations were not observed in the bulk composites. The addition of ZrN resulted in a notable increase in hardness of 237% (182 ± 8 HV2), elastic modulus of 56% (114 ± 3 GPa), compressive and tensile strength of 183% (565 ± 15 GPa), and 125% (387 ± 9 GPa), respectively, for composites containing 30% ZrN, compared to the non-reinforced alloy. Experimentally determined coefficients of thermal expansion (CTEs) for composites with 10%, 20%, and 30% ZrN content were 19.8 × 10−6 °C−1, 19.1 × 10−6 °C−1, and 18 × 10−6 °C−1, respectively, which well relates to Schapery’s model. These findings contribute to understanding the synthesis, mechanical behavior, and thermal properties of ZrN/AlSi10Mg composites, demonstrating their potential for diverse engineering applications.

Mechanical Property and Fracture Behavior of Borazine-Derived Bulk Boron Nitride Ceramics Reinforced with Chopped Si3N4 Fiber

Mechanical Property and Fracture Behavior of Borazine-Derived Bulk Boron Nitride Ceramics Reinforced with Chopped Si3N4 Fiber

Design and analysis of a conical origami tube (COT) composed of quadrilateral unit cells

Abstract Kresling origami are a topic dat are constantly being researched, especially when it comes too,, teh cylindrical mechanisms made up of special quadrilateral units. It's also fascinating dat teh conical mechanisms based on teh Kresling pattern are gaining more attention lately. However, designing conical mechanisms wif stable behavior and solving teh stress concentration in crease areas for practical engineering applications remains less researched. they'refore, dis study considers quadrilateral unit cells as teh research object, designs a conical origami tube (COT), and establishes a theoretical model wif five variables too,, systematically investigate teh COT. Based on dis, teh design domain related too,, teh design variables are proposed, and teh COT are analyzed in three cases. We further explored teh influence of η (conical degree) on teh COT. In addition, dis study implements a cutting design on each crease vertex too,, reduce teh impact of stress concentration on teh nonlinear response through finite element shell models and uniaxial compression experiments. Teh findings of dis study reveal dat teh setting of η and teh crease-cutting design has a remarkable impact on teh mechanical properties and stability behavior.

Mechanical, wear, thermal conductivity and hydrophobicity behavior of Kevlar fiber-epoxy structural composites reinforced with onion peel carbon quantum dot and commercial carbon nanotubes: a comparative study

Mechanical, wear, thermal conductivity and hydrophobicity behavior of Kevlar fiber-epoxy structural composites reinforced with onion peel carbon quantum dot and commercial carbon nanotubes: a comparative study

Investigation of microfriction properties of graphene/AlCoCrFeNi high entropy alloy

Applying graphene (Gr) coatings to high-entropy alloys (HEA) is anticipated to enhance their tribological characteristics. The current understanding of the mechanism by which the Gr/HEA is enhanced at the atomic level is still limited. Molecular dynamics simulations revealed the mechanical behavior and strengthening mechanism of the Gr/AlCoCrFeNi HEA during nanoindentation and nanoscratch. The results demonstrate a substantial increase in the indentation hardness of the Gr/AlCoCrFeNi HEA by about 2.4 times. When Gr changed from a single layer to three layers, it further improved (3.2 times for a double layer and 3.9 times for three layers). At the same time, the friction coefficient is effectively reduced. Furthermore, the elevated in-plane stiffness of the Gr coating leads to an expansion of the effective loading area, resulting in increased Shockley dislocation and stair-rod dislocation density within the Gr/AlCoCrFeNi HEA, thereby amplifying the strain hardening effect and reducing subsurface damage. Qualitative experiments confirmed the excellent wear resistance of the Gr/HEA, and coating Gr increased the width of scratches, effectively confirming our simulation results. These findings provide valuable insights for the development and design of Gr/HEA composite coatings with enhanced mechanical properties.

Mechanical Properties of an Ultrahard In Situ Amorphous Steel Matrix Composite

We report compression tests on micropillars manufactured from bulk specimens of partially devitrified SAM2×5 (Fe49.7Cr17.7Mn1.9Mo7.4W1.6B15.2C3.8Si2.4). Yield strength values of ≈6 GPa are obtained. Such a high strength can be attributed to the higher glass transition temperature (883 K) of this material, which impedes the multiplication of shear bands under loading, and to the presence of hard crystalline domains that result from devitrification of the amorphous powders during powder consolidation. The Vickers hardness of the specimens is found to be strongly correlated to the processing temperature and, hence to the volume of crystalline phases present in the specimens. As the processing temperature is increased, there is a reduction in free volume from the structural relaxation process in the amorphous alloy, leading to the eventual nucleation of crystalline phases of BCC Fe, Cr2B, Cr21.30Fe1.7C6, or Fe23B2C4, during the densification process. These results shed light on the relationship between nanocrystalline domains and the mechanical behavior of Fe‐based amorphous/crystalline composites.

Studying the mechanical behavior of loess-cement mixtures and adopting a cement-soil cushion (CSC) as a shallow ground improvement solution for foundations laying on collapsible soils

In the context of Bulgaria's expanding construction sector, the northern region of the Danube Plain has encountered challenges associated with the subsidence of loess soils upon saturation, characterized by rapid settlement and self-compaction – also known as “collapse”. This phenomenon poses significant risks to construction projects, prompting extensive research into its causes and prevention. One widely adopted method for stabilizing loess soil foundations in construction is the use of cement-soil cushions (CSC). This study's primary objective is to explore and select an effective technology for constructing a suitable composition of a cement-soil (loess-cement) cushion beneath buildings’ foundations in Kozloduy, where the soil is collapsible loess.

Non local Analytical and Numerical modelling of re-entrant auxetic honeycomb

Abstract Auxetic materials, characterized by their negative Poisson’s ratio, have been extensively studied for applications in energy absorption and mechanical reinforcement. Re-entrant honeycomb structures, a subtype of auxetic materials, have demonstrated superior mechanical characteristics. However, understanding the mechanical behavior of these structures at the nanoscale remained a significant challenge. To address this gap, the authors explored the influence of size on the deflection behavior of re-entrant auxetic honeycomb structures through non-local continuum mechanics. Their analytical model, incorporating the Euler-Bernoulli beam model and considering four non-dimensional geometrical parameters, was validated through numerical simulations and a comprehensive review of existing literature. The study aimed to provide valuable insights into the design and engineering of re-entrant auxetic honeycomb structures across diverse applications, contributing to the advancement of non-local elasticity theory and deepening the understanding of the mechanical behavior of auxetic structures at the nanoscale. The research laid a foundation for further exploration and optimization of re-entrant honeycomb structures, facilitating their effective utilization in fields such as MEMS/NEMS by leveraging the dimensionless parameters identified in the study.

Mechanical behavior of multi-layer CORC cable in high external field with 3D numerical model

The degradation of critical current due to mechanical deformation in a high field has a profound impact on the performance of high-temperature superconducting (HTS) structures. The multi-layer conductor on round core (CORC) cable is a widely-applied HTS structure in engineering. Due to the complexity of the multi-layer CORC cable, the contact between the tapes should be considered when simulating the mechanical behavior in high field. In this paper, 3D electromagnetic and mechanical models were developed to investigate the mechanical behavior of the multi-layer CORC cable. Under the same electromagnetic force, the comparisons of mechanical models of a 5-layer CORC cable with different contact methods are presented. Subsequently, the effects of the loading path of the external magnetic field and transport current, the bending geometry of the CORC cable, the winding direction of the HTS tape in the CORC cable, and the shielding current on the mechanical behavior are discussed, respectively. The numerical results are useful for the design and operation of CORC cable in high field.

Study on anisotropic mechanical behavior of AZ31 magnesium alloys under free-end torsion

In this study, the mechanical behavior and microstructure of a hot-rolled AZ31 magnesium alloy sheet under free-end torsion with torsional axis along rolling direction (RD), normal direction (ND) and 45° in ND-RD plane, have been investigated both experimentally and numerically. The mechanical behavior under torsion, including stress-strain response, Swift effect and strain hardening rate, present obvious anisotropy. The Swift effect is sensitive to the direction of torsion axis and exhibits remarkable anisotropy with axial elongation in ND sample and axial shortening in RD and 45° samples. The axial elongation or shortening is determined by both slips and extension twin, with extension twin exerting a greater influence on the extent of the axial deformation. During shear straining, the dominant deformation mode transforms basal slip to prismatic slip with the axial direction deviating from ND to RD, while the second-order pyramidal ⟨c+a⟩ slip is nearly not activated during whole deformation attributed to its high critical resolved shear stress. Based on the effective Schmid factor (ESF) of deformation modes, the grains with favored orientation would get activation of {101‾2} extension twin due to the high ESF, resulting in the different twin volume fractions. Additionally, the activation of twin relative to basal slip has a connection with the increasing trend of normalized strain hardening rate.

The influence of papaya shape on its mass model and mechanical properties

AbstractPostharvest handling tasks include fruit grading and minimizing loss. Fruits are often packaged into grades based on size and mass for uniformity and proper handling. Losses caused by mechanical damage can be reduced by understanding the fruit's response to loads. Papaya's (cv. Exotica) irregular shape and short shelf‐life are important factors for proper handling. This study aimed to develop a model for papaya mass based on geometric properties and to characterize its mechanical behavior when compressed along its major axis. For mass prediction, single‐ and multiple‐variable regression models using papaya's geometrical variables were developed. Despite its irregular shape, similar performance was observed in the best single‐ and multiple‐variable mass models (R2 ≈ 0.95, RMSE ≈ 82 g). However, the single‐variable model is likely more practical because only two axial lengths are needed and can be extracted from 2D images. For papaya's mechanical behavior, the results for elastic properties indicate some variations (p &gt; 0.05) in elastic modulus, and failure stress and strain along the major axis, while results for viscoelastic properties indicate significant variation (p &lt; 0.05) in the relaxation moduli. Overall, the bottom section is less resistant to deformation compared to the top. Therefore, reducing compression in the section could potentially reduce damage. Using the mechanical properties described here in computer simulation studies may provide more detailed load distribution. Mass modeling can aid the automation of papaya grading, while mechanical response characterization provides valuable information for designing postharvest handling systems.Practical ApplicationsPostharvest handling tasks include fruit grading and minimizing loss. Fruits are often packaged into grades based on size and mass for uniformity and proper handling. Losses caused by mechanical damage may be reduced by understanding the fruit's response to loads. Papaya's irregular shape and short shelf‐life are important factors for proper postharvest handling. Mass modeling can assist the automation of papaya sorting, while characterizing its mechanical response can assist the design of postharvest handling systems. The mass model result indicates that papaya's mass (cv. Exotica) can be predicted using two axial lengths, which can be easily obtained using 2D images. The advantage is that this task can be combined with other tasks using imaging data. While the mechanical properties of papaya indicate that its bottom section is more susceptible to deformation compared to the top when they are stored in an environment with minimal movements over an extended period. Therefore, in this setup, applying the compression load at the top section while minimizing compression load at the bottom may be more effective in preventing and minimizing mechanical damage.