Compressive Stress-strain Curves Research Articles

Compressive properties and analytical modelling for stress-strain curves of polyvinyl alcohol fiber reinforced concrete

The use of polyvinyl alcohol (PVA) fibers in the manufacturing of fiber reinforced concrete is considered a technological revolution in the concrete construction industry due to its advantageous mechanical properties. In this regard, this paper presents the experimental and analytical study of three different grades of PVA fiber reinforced concretes (PVAFRCs) i.e., PVAFRC30, PVAFRC50, and PVAFRC70. A total of eighteen mixes developed for three different grades of PVAFRC with various percentages of PVA fibers (0, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%). Workability, and compressive strength, flexural strength, split tensile strength, load-deflection behaviour, and uniaxial compressive stress-strain behaviour of PVAFRCs have experimentally evaluated. The stress ratio, strain ratio, peak-stress, strain at peak-stress, Young’s modulus, compressive toughness index, and energy absorption capacity of PVAFRCs also have been evaluated analytically. The results indicated that the addition of PVA fibers reduced the workability of PVAFRCs mixes and caused significant changes in engineering properties of the concrete. In all three grades of PVAFRC mixes, good mechanical properties exhibited at 0.3% PVA fiber content. The modified analytical model and relationships between material parameter (βn) and modified reinforcing index (MRIV) are proposed to predict the uniaxial compressive stress-strain curves of different grades of PVAFRCs, and a good agreement with experimental results was observed. The existing relationships between material parameter and reinforcing index reported in previous studies for analytical modelling of the experimental compressive stress-strain behaviour of FRC are not able to accurately predict in case of PVAFRCs.

Finite element simulation and experimental verification of quasi-static compression properties for 3D spacer fabric/hollow microspheres reinforced three phase composites

To enhance the compressive properties of syntactic foams, a new type of ternary composite named 3D spacer fabric/hollow microspheres reinforced composite (3DSMRC) was designed by adding warp-knitted space fabric (WKSF) into traditional syntactic foam. In order deeply understand the meso-mechanical properties of 3DSMRC composites, the compression tests of 3DSMRC were carried out and the quasi-static compression finite element models were established based on COMSOL Multiphysics. The results show that the compression properties of 3DSMRC were obviously controlled by structures of WKSF. To be specific, the 3DSMRC composites with more spacer yarns per unit area could withstand higher critical load, and with denser surface layers and larger spacer yarns inclination-angle could gain better compression capacities. Meanwhile, different types of microspheres also had important impact on the compression capacities of specimens, which could be improved by using smaller radius ratio (higher strength) microspheres. In addition, the finite element model can accurately reproduce the compression process and stress-strain curves of representative 3DSMRC samples, and then accurately simulate the values of compressive modulus and yield strength. The simulation and experimental studies of 3DSMRC can help to obtain a better and deeper understanding of the compression properties of this new type of composite, and finally provide a useful theoretical reference for the optimization design of 3DSMRC.

Compressive behaviour of seawater sea-sand concrete containing glass fibres and expansive agents

The development and application of seawater sea-sand concrete (SSSC) can effectively reduce the utilisation of natural resources for producing concrete, thereby protecting ecological environments. However, the durability of reinforced SSSC is an important aspect. Previous studies have shown that the addition of fibres and expansive agents (EAs) can improve the durability of reinforced concrete structures by controlling crack development, reducing concrete porosity, and enhancing the tensile strength of concrete. In this study, the compressive behaviour of SSSC containing glass fibres (GFs) and EAs was studied. Furthermore, tests were performed to evaluate the combined effects of fibre length, GF content, and EA content on the workability of fresh concrete and the failure mechanism, compressive strength, strain at peak stress, and toughness of hardened concrete. It was found that the addition of GFs and EAs significantly improved the compressive performance of SSSC. The characteristics of compressive stress–strain curves were analysed and a constitutive model that could simulate the compressive stress–strain relationship of SSSC containing GFs and EAs was proposed. These outcomes are expected to provide experimental support and theoretical guidelines for designing SSSC structures.

Analysis of compressive dynamic behaviors of plain concrete and lightweight aggregate concrete

In this paper, 8 loading strain rates were configured to carry out experimental research on the compressive dynamic behaviors of plain concrete (PC) and lightweight aggregate concrete (LWAC) by utilizing a hydraulic servo machine. The compressive failure modes and stress-strain curves of PC and LWAC under various loading states were generated from the experiments. The peak stress and peak strain values extracted from the stress-strain curves, as well as the elastic modulus, were comparatively analyzed between the two types of concrete. The experimental findings indicate that the failure mode of PC under the static strain rate mainly manifest as the damage to bonding materials, while the failure under dynamic strain rates involves part of coarse aggregates. For LWAC, the failure modes under both static and dynamic loading mainly manifest as the damage to shale ceramisite. As the strain rate increases, the peak stress and elastic modulus of both PC and LWAC increase significantly. Compared with PC, the strain rate effect on LWAC is more obvious. The peak strain of both PC and LWAC varies insignificantly across different strain rates, even though the changing trend shows a discrete pattern. In addition, on the basis of the experimental results, the relationship equations between the strain rate and the related mechanical parameters were established for both PC and LWAC. It is found that the values of peak stress and elastic modulus and the logarithmic value of the corresponding strain rate after non-dimensional treatment fit a linear relationship. The findings provide theoretical insights into the research and engineering application of LWAC.

An Experimental Study on the Dynamic Mechanical Properties of Epoxy Polymer Concrete under Ultraviolet Aging.

Epoxy polymer concrete (EPC) is widely applied in engineering for its excellent mechanical properties. The impact loads and severe climatic conditions such as ultraviolet radiation, temperature change and rain erosion are in general for its engineering practice, potentially degrading the performance of EPC. In this paper, a procedure of accelerated aging for EPC, imitating the aging effect of ultraviolet radiation and hygrothermal conditions based on the meteorological statistics of Guangzhou city, was designed. After various periods of accelerated aging, the dynamic behaviors of EPC were studied by using a Split Hopkinson Pressure Bar (SHPB). The verification of the experimental data was performed. The two-stage dynamic compression stress-strain curves were obtained: (a) linear growth stage following by strain hardening stage at impact velocity 12.2 m/s and 18.8 m/s, (b) linear growth stage and then a horizontal stage when impact velocity is 25.0 m/s, (c) linear growth stage following by strain softening stage at impact velocity 29.2 m/s. The experimental results show that the specimens after longer accelerated aging tend to be more easily broken, especially at impact velocity 12.2 m/s and 18.8 m/s, while the strain rate is the main factor affecting the compression strength and stiffness. Ultimately the influence of strain rate and equivalent aging time on dynamic increase factor was revealed by a fitting surface.

Effect of geometry on the compression characteristics of bonded brickwork

Bonded brickwork walls of large thickness constructed with double or triple bricks are common in loadbearing historical masonry structures in many regions which require interventions and compression capacity evaluation. However, current design provisions for compression capacity prediction are primarily based on single brick prisms and wallette specimens. Due to anisotropic nature of masonry, the strength and deformation characteristics of bonded brickwork with double and triple brick thicknesses are different to the single leaf brickwork; and their design using the provisions of single leaf bonded brickwork specimens may be un-conservative. To expand the knowledge on the compressive behaviour of bonded brickwork, a detailed numerical investigation has been reported in this paper. A simplified Finite element (FE) based micro-modelling technique was implemented to simulate the compression response of bonded brickwork specimens. The developed FE modelling technique was initially verified against the experimental predictions of compressive capacities and axial stress-strain curves. The numerical modelling results iterated that there was no noticeable increase in the compressive capacity of the masonry with increase in the brickwork thicknesses due to increased number of weak head joints. The validated models were then employed to study the effect of slenderness of the bonded brickwork specimens on the axial compression response. The height to thickness (slenderness) ratios of the bonded brickwork were varied from 1.4 to 10.9 for analysing 30 different cases with two brick strengths. Results showed that with increasing slenderness ratio, the compressive strength of the bonded brickwork reduces for all bonded thicknesses. The parametric study indicates that the slenderness ratio influences the compression characteristics of bonded brickwork specimens; subsequently, correction factors for the compressive strengths determined with different slenderness ratios of brickwork specimens are proposed.

Compressive behavior and vibration-damping properties of porous Ti-6Al-4V alloy manufactured by laser powder bed fusion

• Compressive behavior of porous Ti-6Al-4 V alloy is governed by the relative densities. • Compression mechanism tends to be elasto-plastic in specimens with larger cell size. • Energy absorption capacity increases linearly with the as-manufactured density. • Natural frequency of cellular structure is proportional to the strength-weight ratio. • Cellular structures with larger cell size exhibit better damping abilities. Porous Ti-6Al-4V alloy with various cell geometries and cell sizes was manufactured by laser powder bed fusion (LPBF) technique, and the influence of the structural characteristics on the compressive behavior and vibration-damping abilities was systematically investigated. In terms of the compressive performance, both elasto-brittle and elasto-plastic features are observed from the compressive stress-strain curves and the corresponding transformation from elasto-brittle to elasto-plastic can be achieved by increasing the cell size. Moreover, the compressive performances are found to be closely related to the relative density determined by both the cell geometries and cell sizes of specimens. The energy absorption capability of each cellular structure increases linearly when increasing the as-manufactured density, while the energy absorption efficiency presents sensitivities to both the cell geometry and the cell size. The results also reveal that the variation of natural frequency is proportional to the specific strength (i.e., strength-weight ratio), and the cellular structure with larger cell size exhibits better damping ability than smaller sized structures.

Homogenization of Masonry Wall using Sensitivity Analysis

Though masonry buildings are most impacted during earthquakes, and the construction of masonry structure cannot be completely avoided in all part of the earth, there is no proper study regarding the behavior of masonry structure regarding seismic performance analysis and design. Detailed analysis of masonry structures requires a detailed micro-modeling technique using finite element method which requires complex calculation and numerous parameters for analysis. In this paper, an approximated simplified finite element computational technique for non-linear analysis of masonry wall is proposed using sensitivity analysis for the flow parameter of masonry wall using a macro-modeling approach in which the masonry unit and mortar are homogenized into a single panel. An experimental wall in which the nonlinear analysis was performed was considered and numerical simulation using a macro-modeling approach is performed with the experimental properties in ABAQUS Software. With making numerical model, tensile and compressive stress-strain curve were obtained which were used to prepare concrete damage plasticity model for the modelling of masonry wall. The sensitivity analysis was performed for the determination of viscosity parameter and dilation angle. The model is prepared and run with various changing values of viscosity parameter and the one that matches with the experimental result was selected. In the same way, the model is prepared for various changing values of dilation angle and the one that matches with the experimental result was selected. The final model was prepared with the values of dilation angle and viscosity parameters thus prepared and the nonlinear force displacement relation was obtained. Thus obtained, non-linear force displacement curve is compared with the actual experimental force-displacement curve.

Experimental Study on Biaxial Dynamic Compressive Properties of ECC.

An improved hydraulic servo structure testing machine has been used to conduct biaxial dynamic compression tests on eight types of engineered cementitious composites (ECC) with lateral pressure levels of 0, 0.125, 0.25, 0.5, 0.7, 0.8, 0.9, 1.0 (the ratio of the compressive strength applied laterally to the static compressive strength of the specimen), and three strain rates of 10−4, 10−3 and 10−2 s−1. The failure mode, peak stress, peak strain, deformation modulus, stress-strain curve, and compressive toughness index of ECC under biaxial dynamic compressive stress state are obtained. The test results show that the lateral pressure affects the direction of ECC cracking, while the strain rate has little effect on the failure morphology of ECC. The growth of lateral pressure level and strain rate upgrades the limit failure strength and peak strain of ECC, and the small improvement is achieved in elastic modulus. A two-stage ECC biaxial failure strength standard was established, and the influence of the lateral pressure level and peak strain was quantitatively evaluated through the fitting curve of the peak stress, peak strain, and deformation modulus of ECC under various strain rates and lateral pressure levels. ECC’s compressive stress-strain curve can be divided into four stages, and a normalized biaxial dynamic ECC constitutive relationship is established. The toughness index of ECC can be increased with the increase of lateral pressure level, while the increase of strain rate can reduce the toughness index of ECC. Under the effect of biaxial dynamic load, the ultimate strength of ECC is increased higher than that of plain concrete.

Simulation and Research on Dynamic Crushing of Rod Concrete

The dynamic mechanical properties of waste glass powder concrete are studied, and the dynamic compressive strength, peak strain, stress-strain curve and dynamic enhancement factor change with strain rate and waste glass powder content are analyzed. Based on the HJC model of concrete, the SHPB test was simulated by ANSYS/LS-DYNA software. With the increase of impact pressure, the phenomenon from block spalling to aggregate crushing appears. When the impact velocity is low, several radial through cracks appear in the test block, and the test block is separated into several blocks with larger volume. With the increase of impact velocity, multiple cracks develop simultaneously.

Material Characterization of GFRP Bars in Compression Using a New Test Method

Abstract This article presents a new test method for determining the mechanical properties of glass fiber–reinforced polymer (GFRP) composite bars in compression, namely the compressive strength, compressive modulus of elasticity, ultimate crushing strain, and compressive stress-strain curves of the bars. The contribution of GFRP bars in compression is currently neglected by major design guidelines related to GFRP-reinforced concrete columns. However, the demand for using GFRP bars is increasing because multiple researchers have shown the effectiveness of the bars in concrete columns. Thus, the need for characterization of the mechanical properties of GFRP bars is increasing, while there is no standardized test method to evaluate the compressive properties of these bars. Therefore, in this article, a new test method is proposed for evaluating the compressive characteristics of GFRP bars. The proposed test method was examined through testing a total of 35 specimens. It was observed that the test method was able to evaluate the compressive characteristics of the GFRP bars successfully. Three different modes of compressive failure were observed, which were related to the crushing of GFRP bars in different locations in the bar, but no premature failure or bar buckling was observed. Moreover, a comparison between tensile and compression characteristics of the GFRP bars showed that the tensile test results are not sufficient to estimate the compressive characteristics, and performing a compression test is necessary.

Uniaxial compressive properties of ecological concrete: Experimental and three-dimensional (3D) mesoscopic investigation

In this study, the uniaxial compressive behaviors of ecological concrete were investigated using experimental and numerical methods. The uniaxial compressive test was performed on the cubic specimens with a side length of 150 mm. The three-dimensional (3D) mesoscopic model with the consideration of random shapes and sizes of aggregates was developed. The parameters considered were the aggregate-to-cementitious material ratio (A/C), the water-to-cementitious material ratio (W/C), the aggregate size, and the void content. The results indicate that the collapse of aggregate caused by the sliding failure of bonding points among aggregates is the main failure mode of ecological concrete under uniaxial compression. The void content and compressive strength of ecological concrete are associated with the A/C and W/C, and the A/C of 6 is suggested as the optimal value. The compressive stress-strain curve consists of three parts, in which the platform period represents the yield period that is relative to the compacting process. Besides, the peak stress and the peak strains in the axial- and lateral directions are related to the void content and aggregate size, and the lateral strain is obviously larger than the axial strain. Through the comparison of numerical and test results, the developed 3D mesoscale modelling approach together with the model parameters has been approved in investigating the compressive behaviors of ecological concrete.

Compressive properties and energy absorption behavior of Mg17Al12/Al ordered structure composites

In this study, Mg17Al12/Al ordered structure composites were prepared by infiltrating the ordered porous aluminum with the intermetallic compound Mg17Al12 under gravity condition. Their compressive properties and energy absorption behavior were investigated by quasi-static compression tests. The results showed that Mg17Al12/Al ordered structure composites exhibited distinctly different compressive stress-strain curves with a prominent linear elastic stage and had an advantage over ordered porous aluminum and Mg17Al12/Al composites with irregular structures on mechanical properties. Moreover, Mg17Al12/Al composites with strengthened truss structure showed better compressive properties than Mg17Al12/Al composites with basic truss structure. The ordered porous aluminum that acted as matrix skeleton showed great plasticity and ductility while the intermetallic compound Mg17Al12 as filler exhibited high compressive strength and obvious brittleness. The improvement of mechanical properties of Mg17Al12/Al ordered structure composites was attributed to the ordered composite structure and the distinct mechanical property of co-continuous intermetallic compound Mg17Al12 and pure Al.

Computational Modeling of Compressive Behavior of Wire-Reinforced Bulk Metallic Glass Matrix Composites

The effect of wire type and volume fraction on the compressive behavior of wire-reinforced bulk metallic glass (BMG) matrix composites were investigated using the finite element method. The composites and test procedure were simulated in the ABAQUS software, and analyses on stress propagation and extracted compressive stress–strain curves were performed, which showed an acceptable agreement with experimental results. The results exhibited that Ta, Mo, W and Stainless Steel type 302 as the reinforcement wires significantly improved the plastic strain of the composites. Meanwhile, W wires sustained the composite strength in the same level of monolithic BMG, without sacrificing noticeable plastic strain of the composite in comparison with other reinforcements. The different volume fractions of W wires showed that the trend of plastic strain progress with increase in the second phase reaches a maximum at 65% of reinforcements. This behavior is caused by the fracture mechanism of the composites which is in its optimum condition when the reinforcement volume fraction is equal to 65%. The mechanical properties of the wire-reinforced BMG composites can be modeled by using the iso-strain Voigt model, which allows the prediction of the mechanical properties of a composite from the volume-weighted averages of the components properties. The above-mentioned findings corroborate the experiments elsewhere and may be considered as a valuable starting point to lead the future researches.

Dynamic crystal plasticity modeling of single crystal tantalum and validation using Taylor cylinder impact tests

In this work, we extend a dislocation-density based constitutive theory for the dynamic thermomechanical behavior of crystals to body centered cubic (BCC) tantalum. Strain rate and temperature dependence of the slip resistance in the model is incorporated via an expression for the state-dependent instantaneous saturation dislocation density and a dynamic recovery fraction that affects the rate of generation of immobile dislocation density. Crystallographic slip along 111 on the {110} or {112} planes as well as their combination are examined. The Schmid stress serves as the driving force for dislocation motion and the twinning/anti-twinning sense of slip on {112} planes is accounted for by introduction of Peierls stress that depends upon this sense. The model parameters are calibrated using a two-stage Bayesian approach against experimentally generated uniaxial stress-strain compression curves at quasi-static and high strain rates over a range of temperatures. Velocity-time histories from single crystal flyer plate impact experiments were also used to parameterize this model. The calibrated model was applied to simulate previous Taylor cylinder impact experiments. Our results show that the model must include slip on {110} and {112} planes and also account for the twinning versus anti-twinning sense of slip on {112} planes, to appropriately represent the orientation dependence of the flow stress and match the deformed geometry of the single crystal Taylor cylinders.

Exfoliated two-dimensional molybdenum disulfide reinforced epoxy syntactic foams

In this paper, we report the effect of introducing molybdenum disulfide (MoS2) nano-platelets: a two-dimensional metal chalcogenide, on the mechanical properties of hollow glass microballoon (HGM)–epoxy syntactic foams. MoS2 reinforced syntactic foams were prepared by mixing MoS2 nanoplatelets to epoxy containing HGMs; with the amount of MoS2 being varied from 0.01 to 0.04% v/v, while maintaining a constant total filler volume fraction of 40% for all compositions. The mechanical behaviour of reinforced syntactic foam was studied under varied loadings including compressive, tensile and flexural under different strain rate regimes. Introduction of MoS2 led to significant improvements in characteristic mechanical properties, particularly in terms of compressive strength and toughness, which suggest intercalation of MoS2 within the epoxy matrix; however, the presence of relatively larger MoS2 micro particles couldn’t be completely negated. The toughness of the foam, as indicated by the area under the compressive stress-strain curve, was found to increase by ∼21% under optimal conditions. Our results highlight the potential of the two-dimensional MoS2 sheets as a reinforcing agent in syntactic foams.

Compressive stress-strain model and residual strength of self-compacting concrete containing recycled ceramic aggregate after exposure to fire

The present study uses recycled ceramic aggregates (RCAs) as a partial replacement of natural coarse aggregate (NCA), to produce two self-compacting concrete (SCC) types, the first containing Portland cement, and the second a calcium-aluminate cement. The residual behavior in compression, after heating to five reference temperatures (110, 200, 400, 600, and 800 °C) is investigated, besides the behavior at room temperature. For both SCC types, three mixes were prepared with different substitution ratios (RCA/NCA = 0, 25 and 50% by mass), and such properties as slump flow and flow time (at the fresh state), and compressive strength, modulus of elasticity and strain at the peak stress (after hardening) were measured. The results confirm that using calcium-aluminate cement brings in a sharp decrease in the mechanical properties at high temperature and indicate that adding RCA has a negligible effect on the mechanical performance at high temperature (with an improvement at 800 °C, 16–86%), but slightly decreases the flowability at the fresh state. For each reference temperature, the stress-strain curves in compression were measured after cooling, but - besides the gain in terms of compressive strength - the general shape of the curves was affected by the substitution ratio. Comparisons are made too with code provisions and previous studies. Last but not the least, predictive equations taken from the literature are used to fit the stress-strain curves to incorporate the effect of recycled ceramic aggregate in SCC in compression at high temperature, and the fitting of the test results appears to be very satisfactory.

The compressive behavior and energy absorption performance of nano-crystalline porous magnesium fabricated by hydrogenation-dehydrogenation and spark plasma sintering technique

Porous magnesium is a new structural and functional composite material. Its special structure gives it excellent properties and widely application prospect. In this paper, nano-crystalline porous magnesium was synthesized by a combined processing of hydrogenation-dehydrogenation (HD) and spark plasma sintering (SPS) process without using blowing agents. Compared with those samples prepared by traditional powder metallurgy (TPM) method containing blowing agents, the HD-SPSed sample possesses higher porosity (28.7%) and smaller sizes and more uniform distribution of the pores. Therefore, relatively higher compression yield strength (29 MPa) and plateau stress are acquired in the compressive stress-strain curve. Furthermore, the relatively smoother stress plateau stage of the sample reveals its great potential in the application of energy absorption materials. The energy absorption, maximum energy absorption efficiency and ideal energy absorption efficiency of the HD-SPSed porous Mg could reach up to 14.9 MJ/m3, 1.90 and 1.41, respectively.

Mechanical properties and constitutive analyses of basalt fiber crumb rubber mortars in soft rock roadways

Uniaxial compressive stress-strain curves of several groups of basalt fiber crumb rubber mortars (BF-CRM) with different contents are tested. By comparing with the GZH model, the improved values of the parameters of the BF-CRM constitutive model based on the GZH model are obtained. Then, taking the supporting scheme of main substation of the mine as the background, using FLAC3D to simulate the roadway support, using BF-CRM to replace the ordinary mortars in the original support, and combining with the triaxial compression test of different confining pressure, the application effect of BF-CRM in roadways support is studied and analyzed.

Mechanical properties of high-strength steel–polyvinyl alcohol hybrid fibre engineered cementitious composites

ABSTRACT With the advancement of material technology, the use of high-strength and high-performance materials in the construction industry is gaining popularity. Steel–polyvinyl alcohol (steel–PVA) hybrid fibre engineered cementitious composites (ECC) is one of such high-performance class of construction materials whose mechanical properties are not well studied in the literature especially in high-strength matrix. Therefore, in this paper, the mechanical properties of four different grades of high-strength steel–PVA ECC are experimentally investigated. ECC with nominal compressive strengths from 60 to 100 MPa are developed. Their mechanical properties including compressive and tensile stress–strain behaviour, elastic modulus and toughness are studied with particular focus on high-strength matrix. Test results show that the developed steel–PVA ECC could achieve good tensile (~0.8%) and compressive (~0.5%) ductility for general structural applications. Simple empirical relationships to predict the elastic modulus and tensile strength of the developed steel–PVA ECC as a function of their compressive strength are suggested. Moreover, an analytical model to generate a complete compressive stress–strain curve of the high-strength steel–PVA ECC is proposed and verified against the experimental results. The proposed stress–strain model would present a useful reference for non-linear analysis of structural elements utilising steel–PVA ECC.