Stress-strain Characteristics Research Articles

Experimental study on the interface bonding characteristic of polyurethane and pavement materials

As a new grouting material, polyurethane has been used in the repair engineering of longitudinal joint distress of semi-rigid base asphalt pavement. It is necessary to study the bonding characteristics of the interface between polyurethane and road materials. In this paper, the interface characteristics of composite materials were considered from the two materials about pavement material and base material. Shear test and split tensile test were carried out on the specimens with different interface roughness and polyurethane density. Based on the test data, the strength models of shear strength and splitting tensile strength with roughness and density were established. The micro-characteristics of the composite interface were analyzed. Polyurethane formed a dense film at the interface, and the film thickness increases with the increase of density. The failure mode of the specimen was affected by the polyurethane film. In addition, the influence of normal stress is considered in the shear test, and the friction angle of the interface was analyzed. The stress-strain curve characteristics of shear test and split tensile test of two kinds of composite materials were summarized. The failure modes were generally three types: failure along the boundary of polyurethane material, failure along the boundary of base material, and joint failure of polyurethane material and base material along the interface. The research results provide a basis for better understanding the influencing factors and failure modes of the bonding characteristic between asphalt mixture, cement stabilized macadam and polyurethane materials.

A Composite Analogy to Study the Linear Elasticity of a Pressurized Latex Tube with Application to a Mechanical Vocal Fold Replica

Mechanical deformable vocal fold replicas are an inherent part of physical studies of the fluid–structure interaction underlying vocal folds auto-oscillation during voiced speech sound production. In this context, the current work considers the linear stress–strain characterization of a pressurized latex tube vocal fold replica. An imaging approach is developed to measure the effective low-strain linear Young’s moduli along the streamwise (49[Formula: see text]kPa) and transverse main auto-oscillation (44[Formula: see text]kPa) directions. Next, a composite analogy is proposed to model the replica’s structure as an equivalent de-homogenized multi-layer material with two, three or four layers. This way equivalent low-strain Young’s moduli of each equivalent single layer can be estimated. Both measured effective and modeled equivalent low-strain Young’s moduli are within the range up to 65 kPa associated with human vocal folds. Resulting equivalent composite representations are of interest for the future design of pressurized latex tube replicas. This is illustrated considering the influence of outer layer latex properties on the overall estimate of the effective Young’s modulus. The proposed analogy is thus efficient in contributing to the direct comparison, in terms of low-strain elastic behavior, between replicas.

Stress-Strain Characteristics Before the 2021 Ms 6.4 Yangbi Earthquake in Yunnan Province, China, and Implications for the Seismogenic Mechanism

Stress-Strain Characteristics Before the 2021 Ms 6.4 Yangbi Earthquake in Yunnan Province, China, and Implications for the Seismogenic Mechanism

Compression and energy absorption characteristics of short fiber‐reinforced 2D composite lattices made by material extrusion

AbstractWith the advent of additive manufacturing, lattice structures have been of increasing interest for engineering applications involving light‐weighting and energy absorption. Several studies have investigated mechanical properties of various lattices made up of mostly unreinforced polymers and lack numerical analysis for reinforced lattice structures. In this paper, mechanical response of short fiber reinforced lattice structures under compression is investigated through experiments and numerical simulations. Three different 2D lattices namely, square grid, honeycomb, and isogrid along with their rotated counterparts were fabricated using 15% wt carbon fiber‐acrylonitrile butadiene styrene and experimentally evaluated through uniaxial compression testing up to 30% strain. As simulations on fiber‐reinforced lattices under large compressive strains are rarely performed and published, finite element models accounting for fiber orientation induced anisotropic mechanical properties and geometrical imperfections were developed to predict the stress–strain characteristics up to 30% compressive strains. The stress–strain curves predicted from the numerical simulations matches well with the experimental responses for various lattice geometries. Various failure mechanisms such as thin strut buckling, contact within the lattice, and fracture of struts under large deformation were investigated. Analyzing energy absorption characteristics of these lattices revealed that the honeycomb structures in horizontal configuration exhibits superior energy absorption capability.

In-situ measurement of anisotropic Young’s modulus in fused deposition modeling printed cantilevers

In this study, we investigate the effect of fused deposition modeling printing direction on the effective Young’s modulus value of cantilevers. Through finite-element simulations and experiments with seven different dimensions and totaling over 100 cantilevers, we have observed the impact of printing direction on cantilever resonance. Unlike the conventional compressive and tensile stress—strain characterization, observation of the resonance allows for in-situ testing on the final device under test during operation. Initially, we observed the bulk filament modulus to be 4.5 GPa based on the optimal match between experiments and realistic finite element models expressing the internal structures of the longitudinal and transverse printed cantilevers. Then, the effective Young’s modulus of the cantilevers is inferred through sweeping the Young’s modulus that provides the best fit between the experiments, conventional cantilever formulations and finite-element simulations with solid, homogeneous, and isotropic cantilever model. Overall, we observed an average effective Young’s modulus of 3.35 GPa for the cantilevers with longitudinal (along the cantilever axis) deposited filaments and an average effective Young’s Modulus of 2.50 GPa for the transverse (perpendicular to the cantilever axis, along the width dimension) deposited Polylactic acid cantilevers. Eventually, simplified shape outline and effective Young’s modulus for the corresponding printing direction eases the subsequent theoretical and simulation analyses. The presented methodology is also applicable to micrometric and sub-micrometric scale serial manufacturing techniques (i.e. two-photon polymerization) where the laser beams steering direction causes anisotropy in the mechanical properties of the device under test.

Compression and Fatigue Testing of High-Strength Thin Metal Sheets by Using an Anti-Buckling Device

BackgroundThe modelling of the sheet metal forming operations requires accurate and precise data of the material plastic behaviour along non-proportional strain paths. However, the buckling phenomenon severely limits the compressive strain range that could be used to deform thin metal sheets.ObjectiveThe main aim of this paper was to propose an effective device, that enables to determine of accurate stress-strain characteristics of thin metal sheet specimens subjected to axial deformation without buckling and with a special emphasis on friction correction.MethodsIn this paper, an anti-buckling fixture was proposed to assess the deformation characteristics of X10CrMoVNb9-1 (P91) power engineering steel, and DP500 and DP980 dual-phase steels, under compression loading. The fixture enables monitoring of the friction between the specimen and supporting blocks during the test, and thus the precise stress response of the material could be determined.ResultsThe effectiveness of the fixture was evaluated under tension–compression cyclic loading and during the compression tests in which high-strength thin metal sheets were successfully deformed up to 10% without specimen buckling. Furthermore, the successful determination of a friction force variation between supporting blocks and the specimen during tests enabled to determine an actual force acting on the specimen.ConclusionsThe proposed testing fixture was successfully assessed during the compression and cyclic tension–compression of high-strength thin metal sheets as no buckling was observed. Its advantage lies in adapting to change its length with specimen elongation or shrinkage during a test. The friction force generated from a movement of both parts of the device could be effectively monitored by the special strain gauge system during testing and thus its impact on the stress-strain characteristics could be successfully eliminated.

Thermal-Fluid-Solid coupling mechanism of a novel friction reduction cooling structure for gas turbine

To supply the higher safety design demands of the new generation of gas turbines, it is urgent to solve the difficulties in mid-chord region of high-temperature turbine blades, including excessive friction loss of traditional two-pass channel, lack of experimental data, lack of stress-strain characteristics in the solid domain and so on. Therefore, this research aims to propose an integrated method of the high-efficiency and low-friction cooling design and Thermo-Fluid-Solid (TFS) coupling analysis. Firstly, a turbine blade rotating cooling experimental system is designed and built independently. Then, a novel friction reduction method with cross bridge structure is proposed. The friction reduction mechanism and the effect mechanism of the cooling performance on the solid strain are revealed through experimental test and TFS coupling numerical study. The results show that the cross brige has an excellent friction reduction effect on the channel. The influence of ‘peak cutting and valley filling’ effectively enhances the heat transfer uniformity as well as successfully reduces the overall strain. The average Nu/Nu0 of the leading edge surface decreases by 14.7% (stationary condition) and 16.4% (rotating condition), respectively. And the Nu/Nu0 of the trailing edge surface achieves a maximum improvement effect of 3.3%. The f/f0 of each channel decreases initially and followed by an increase as Ro increasing. Among them, the channel with two and three cross bridges can achieve friction reduction effects of 24.7–37.3% and 32.2–40.9%, respectively. The strain is related to the Nu/Nu0 of each region, and the value of the rotating trailing edge surface is generally higher than that of the rotating leading edge surface.

Dynamic stiffness of polyester fiber mooring ropes: Experimental investigation based on radial basis function neural networks

Traditional steel wires are being replaced with mooring ropes made from synthetic fibers in offshore industries. However, under the long-term influence of a wave load, the dynamic response of a rope is extremely complex. This paper presents a comprehensive experimental study of the nonlinear dynamic stiffness of polyester fiber mooring ropes under cyclic loading. The stress–strain characteristics of the fiber ropes were investigated based on experimental data. Moreover, cyclic load tests with different mean loads, load amplitudes, and cycles were conducted to study the effects of these three parameters on dynamic stiffness. In previous studies, the dynamic stiffness of fiber ropes was estimated using empirical equations. In this study, the self-learning ability of a radial basis function (RBF) neural network was used to predict the dynamic stiffness of polyester fiber ropes. The predicted results were compared with the empirical formula calculations and experimental measurement results. The RBF neural network has better prediction results than the empirical formulation. In addition, the autonomic learning of the neural network was better when the sample data were in a disordered input state than in an ordered input state. The research findings of this study provide new approaches for solving the dynamic stiffness of ropes and lay a theoretical foundation for the mechanical analysis in the engineering design stage of mooring systems.

Discrete element simulation of the hydrate-bearing sediments mechanical behaviors under typical hydrate dissociation patterns

The hydrate-bearing sediments (HBS) mechanical properties during hydrate dissociation are important to the safe, efficient and sustainable exploitation of natural gas hydrates (NGH). However, the inhomogeneous hydrate dissociation patterns inherent to HBS may make it difficult to accurately obtain its mechanical properties. In this study, a discrete element method (DEM) model was adopted to simulate the HBS mechanical behavior under various hydrate dissociation patterns. By investigating the simulation results and the corresponding internal mechanism, it is found that the stratified and radial inhomogeneous hydrate dissociation in HBS significantly affects its stress‒strain characteristics, and HBS under radial hydrate dissociation has a larger deviation. Moreover, it is suggested that when designing experiments to study the hydrate dissociation effect on the HBS mechanical strength, if the hydrate dissociation homogeneity cannot be guaranteed, a preference for a stratified hydrate dissociation pattern can lead to more desirable results. Finally, a method to judge the HBS hydrate dissociation pattern was also proposed. The results have a guiding significance for the experimental study of HBS mechanisms under hydrate dissociation and ultimately contribute to the realization of accurately predicting reservoir mechanical behavior during NGH exploitation.

A coupled FEM-DEM study on mechanical behaviors of granular soils considering particle breakage

Particle breakage often occurs in the fields of geological, geotechnical and hydraulic engineering like rock avalanche, landslides and high earth-rock dam, which affects the design and countermeasures of relevant engineering structures. Investigation of particle breakage’s effect on mechanical behaviors of granular soils has always been the hotspot within the community of particulate materials. In this study, a coupled finite element method (FEM) and discrete element method (DEM) modeling has been developed to tackle boundary value problems (BVPs) related with particle breakage. In the method, the particle breakage simulation is implemented in DEM through the conventional bonded particle modeling (BPM), while the stress–strain characteristics of representative volume element (RVE) captured by DEM is directly transmitted into the FEM solver to avoid the complicated and phenomenological constitutive equations incorporating into particle breakage. As an illustration, we apply the proposed multiscale modeling to investigating mechanical behaviors of quartz sands subjected to particle breakage through the high confining pressure biaxial compression simulation. And effects of particle strength, particle shape and confining pressure on particle breakage characteristics and further mechanical behaviors of quartz sands are also discussed accompanied with the underlying micromechanisms. Results demonstrate that the coupled FEM-DEM modeling can be able to deal with the complex geomechanics problems involving particle breakage.

Analysis of Electrical Resistivity Characteristics and Damage Evolution of Soil-Rock Mixture under Triaxial Shear.

Construction of engineering structures in geomaterials with soil-rock mixture (S-RM) is often a challenging task for engineers. When analyzing the stability of the engineering structures, the mechanical properties of S-RM often receive the most attention. To study the mechanical damage evolution characteristics of S-RM under triaxial loading conditions, a modified triaxial apparatus was used to conduct shear test on S-RM, and the change of electrical resistivity was measured simultaneously. The stress-strain-electrical resistivity curve and stress-strain characteristics under different confining pressures were obtained and analyzed. Based on the electrical resistivity, a mechanical damage model was established and verified to analyze the damage evolution regularities of S-RM during shearing. The results show that the electrical resistivity of S-RM decreases with increasing axial strain and that the differences in decrease rates correspond to the different deformation stages of the samples. With the increase in loading confining pressure, the stress-strain curve characteristics change from a slight strain softening to a strong strain hardening. Additionally, an increase in rock content and confining pressure can enhance the bearing capacity of S-RM. Moreover, the derived damage evolution model based on electrical resistivity can accurately characterize the mechanical behavior of S-RM under triaxial shear. Based on the damage variable D, it is found that the damage evolution process of S-RM can be divided into a non-damage stage, a rapid damage stage and a stable damage stage. Furthermore, the structure enhancement factor, which is a model modification parameter for the effect of rock content difference, can accurately predict the stress-strain curves of S-RMs with different rock contents. This study sets the stage for an electrical-resistivity-based monitoring method for studying the evolution of internal damage in S-RM.

The influence of aspect ratio on the determination of tearing energy in mode I fracture tests

The energy for tearing is a classical measure of fracture toughness for elastic materials at finite strains. The prominent approach to quantify the tearing energy utilizes a tensile test on edge-cut thin rectangular specimens with low height-to-width ratio to determine the critical stretch at which a crack propagates from the tip of the cut. The analysis of the experiment, proposed by Rivlin and Thomas (1953), relies on the assumption that a large portion of the test piece is in a state of plane strain, and that the change of the total elastic energy is equal to the energy release due to the formation of new crack surfaces. While these assumptions are well justified for test pieces with sufficiently low height-to-width ratio, limitations in the availability and homogeneity of various sample materials have enforced the use of specimens with higher height-to-width ratios. In order to analyse the applicability of the classical theory and the corresponding errors, we investigate in the present work the influence of the sample’s height-to-width ratio on the estimation of the tearing energy in mode I fracture tests. Exemplified with experiments and simulations for the elastomer Ecoflex 1:1, we show that reliable measurements can be obtained even for a quadratic sample geometry. For tough materials, however, significant overestimation of the tearing energy is expected already for a height-to-width ratio larger than 1/2. Surprisingly, in very brittle materials the tearing energy is vice-versa prone to be underestimated by up to 10% for ratios up to 1. The error also depends on the non-linear stress–strain characteristics, as illustrated by the use of different constitutive models. While a generally valid geometrical criterion cannot be defined based on the present results, our results suggest that the error hardly exceeds 10% for height-to-width ratios of up to 1/2.

Bauxite residue as a binary additive in lime treated soil composites

Industrial solid wastes have been valorized as binary and ternary admixtures in earth modification and treatment of problematic soft soils. In this investigation, an industrial waste from the aluminium industry, viz. Bauxite Residue was assessed to understand its efficacy as a binary addendum to lime in improving swelling soils. The novelty of this investigation is its focus on the combination of a scientifically established lime content viz. optimum lime content and low doses of Bauxite Residue, which seems to be virtually absent in published literature. The investigational trial explored the unconfined compression strength and stress–strain characteristics of the lime treated soil composites, treated using combinations of 7% lime and 0.25%, 0.5%, 1% and 2 % bauxite residue. The lime treated soil composites were moulded in to cylindrical specimens of 38 mm diameter and height of 76 mm, cured in air-tight polyethene covers for two hours, three, seven, fourteen and twenty-eight days and tested for their unconfined compression strength. The outcome of the investigation was also compared with some previous investigations from available literature. It was revealed that 2% bauxite residue blended lime treated soil composites was the most ideal out of all combinations studied for developing maximum strength of the lime treated soil composites. It was also noticed that bauxite residue blending of the lime treated soil composites did not affect the strength progression trends irrespective of the bauxite residue content and post peak stress–strain behaviour of the lime treated soil composites improved with increasing bauxite residue content.

Research on the Characteristics of Acoustic Emission Activities of Granite and Marble under Different Loading Methods

Abstract At present, there is no corresponding standard for the engineering application of rock acoustic emission technology. To better apply acoustic emission technology to engineering practice, in this paper, the acoustic emission characteristics of different rock samples of marble and granite under uniaxial compression were analyzed by indoor acoustic emission test, the factors affecting the acoustic emission characteristics of rocks are studied, and the failure mechanism and damage characteristics of rock are discussed. The research contents include analyzing the curve fitting relationship between the acoustic emission event rate, the number of events, the stress time, and study of the similarities and differences of acoustic emission characteristics of marble and granite; analysis of damage characteristics of marble and granite based on acoustic emission parameters; by analyzing the relationship between the Felicity ratio of different rocks and the stress level during cyclic loading, the applicability of studying the Kaiser and Felicity effects of rocks; variation of acoustic emission event rate and rock peak intensity under different loading methods and loading rates. The results show that the acoustic emission of marble and granite has experienced the initial compaction zone, the rising zone, the peak zone, and the falling zone, and the two kinds of rocks have different acoustic emission phenomena in different stages, and the duration of each stage is also different; before the instability of the two kinds of rocks, there is a quiet period of acoustic emission, and the higher the rock strength, the longer the duration of this quiet period, which means that the calm period can be used as a precursor feature of rock mass instability for disaster prediction; during the cyclic loading process of rock, the damage development law is divided into three stages: initial stage, stable stage, and instability stage. When the Kaiser effect did not appear for the two rock stresses before 20%, between 20% and 70% of the peak strength, the Kaiser effect is obvious. When the stress exceeds 80% of the peak value, the Kaiser effect fails, and the Felicity effect appears; the variation of the loading rate affects the variation of the acoustic emission event rate, and the increase of the loading rate leads to aggravated rock damage. The theoretical stress-strain curve can reasonably reflect the actual stress-strain characteristics of rock by combining the number of acoustic emission events with the rock damage model. The results are consistent with the acoustic emission test, which verifies the inevitable relationship between acoustic emission and damage to the rock.

Stress-Strain Relationship of Clay in Dongting Lake Area Based on Three Damage Factors

CU test and CD test were performed to capture the stress-strain characteristics of the clay in Dongting Lake area, China. Since the classical constitutive model cannot ideally describe the strain hardening behavior of the clay, an improved constitutive model that involved three damage factors was proposed. The damage first factor D 1 , which represents elemental volume strength F , was fitted by the Weibull function. The second and third damage factors D 2 and D 3 , which represent the porosity ratio e and the drainage rate P ε respectively, were fitted by Harris function. The CD test damage model is constructed by D 1 , D 2 , and D 3 . In the CU test, the porosity ratio e is a constant value, and the drainage volume is 0, so that D 2 is constant value and D 3 is 0. Therefore, the CU test damage model of the clay was constructed using the damage first factor D 1 . In the end, the accuracy of the proposed CU/CD damage constitutive models of the clay was validated with the experimental results. It is found that the results fitted by the proposed methodology are in good agreement with the experimental results.

Stress-strain characteristics of 3D-braided yarn preform

Composite researchers have not realized the potential of 3D-braided yarn preforms due to limited knowledge about their stress-strain aspects. This research presents a simple model to predict stress-strain characteristics of 3D-braided sisal yarn preforms by considering the yarn's reorientation under tensile load. The 3D-braiding machine having four carriers in the rows and columns, was used to develop 3D-braided sisal yarn preforms by varying the surface braiding angles. The experimental values were compared with predicted results, and a very good agreement was observed between them.

Mechanical Properties and Constitutive Relationship of Cretaceous Frozen Sandstone under Low Temperature

During the construction of coal mine shafts through Cretaceous water-rich stratum using the freezing method, the frozen shaft lining can break and lose stability. Hence, it is necessary to examine the mechanical properties and constitutive relationship of Cretaceous water-rich sandstone under the effect of surrounding rocks. To this end, in this work, the mechanical properties of red sandstone at different confining pressures and freezing temperatures were examined by using a ZTCR-2000 low-temperature triaxial testing system, wherein the 415–418 m deep red sandstone in the Lijiagou air-return shaft of Wenjiapo Mine was taken as the research object. The test results indicated that the stress–strain curves of rock under triaxial compression and uniaxial compression presented four stages: pore compaction, elastic compression, plastic yield, and post-peak deformation. The difference between the two cases was that the post-peak curve of the former was abrupt, while the latter exhibited a post-peak strain softening section. As the freezing temperature was constant, with the raise in the confining pressure, the elastic modulus and peak strength of the rock rose linearly, while the Poisson’s ratio decreased quadratically. As the control confining pressure was constant, the elastic modulus and rock’s peak strength increased with the decrease in the temperature, and under the condition of negative temperature, the two parameters were linearly correlated with the temperature, while the Poisson’s ratio showed the opposite trend. The two-part Hooke’s model and the statistical damage model based on Drucker–Prager (D-P) yield criterion were used to establish the stress–strain relationship models before and after the rock yield point, optimize the model parameters, and optimize the junction of the two models. The results revealed that the optimized model curve was in good agreement with the experimental curve, which suggests that the proposed model can accurately describe the stress–strain characteristics of rock under three-dimensional stress. This verified the feasibility and rationality of the proposed model for examining the constitutive relationship of rocks.

Laboratory studies of the dynamic characteristics of mechanically-biologically treated waste.

The dynamic characteristics of landfills under seismic loading and their stability strongly depend on the cyclic stress-strain characteristics of the waste. An accurate assessment of the dynamic characteristics of mechanically-biologically treated (MBT) waste is crucial to the construction and safe operation of landfills. Considering the effects of the confining pressure, strain amplitude, and loading frequency, 72 sets of consolidated undrained cyclic triaxial (CTX) tests were conducted on MBT waste. Our results showed that the dynamic stress amplitude of MBT waste increases with increasing strain amplitude and decreases with increasing number of cycles. Furthermore, the shear modulus of MBT waste increases with the increase in the confining pressure and decreases with the increase in the strain amplitude. By increasing the strain amplitude, the damping ratio of MBT waste increases. However, the shear modulus and damping ratio of MBT waste are less affected by the loading frequency. A modified Davidenkov model is presented, which describes the correlations among the normalized shear modulus of MBT waste, shear strain, and confining pressure. The fitting parameters are discussed, and the correlation between the normalized shear modulus and shear strain of MBT waste and that between the normalized shear modulus and shear strain of municipal solid waste were compared. The results of this study can be used as references for analyses of the dynamic stability of MBT landfills.

Quasi-Static Investigations of 240-Bloom Gelatine for Ballistic Tests

The paper presents the results of investigations of ballistic gel properties in quasi-static conditions. Specimens were prepared using the 240 Bloom gelatine, which was determined by product availability. Tests were carried out making use of a material testing machine to estimate the influence of gel share on stress-strain characteristics. Considered values of a gel mass content were equal to 10, 12, and 14%. Assumed parameters were determined on the material calibration stage conducted with steel balls with a diameter of 4.5 mm. The most significant influence of a gel content on mechanical properties of specimens were observed for a share of 10% and 12%. The conducted preliminary tests are a part of investigations aimed at assessment if it is possible to calibrate the ballistic gel making use of mechanical characteristics obtained in quasi-static tests without shooting.

Mechanical properties and damage constitutive model of sandstone after acid corrosion and high temperature treatments

Aiming at the problem of temperature-mechanics-chemical (T-M-C) action encountered by rocks in underground engineering, sandstone was selected as the sample for acid corrosion treatment at pH 1, 3, 5 and 7, the acid corrosion treated samples were then subjected to high-temperature experiments at 25, 300, 600, and 900 °C, and triaxial compression experiments were conducted in the laboratory. The experimental results show that the superposition of chemical damage and thermal damage has a significant impact on the quality, wave velocity, porosity and compression failure characteristics of the rock. Based on the Lemaitre strain equivalent hypothesis theory, the damage degree of rock material was described by introducing damage variables, and the spatial mobilized plane (SMP) criterion was adopted. The damage constitutive model can well reflect the stress-strain characteristics of the rock triaxial compression process, which verified the rationality and reliability of the model parameters. The experiment and constitutive model analyzed the change law of mechanical properties of rock after chemical corrosion and high temperature thermal damage, which had certain practical significance for rock engineering construction.