Compressive Constitutive Model Research Articles

Time-varying compressive properties and constitutive model of EPDM rubber materials for tunnel gasketed joint

The stress relaxation of ethylene propylene diene monomer (EPDM) rubber material in a compressed state significantly increases the risk of water leakage at tunnel precast segmental joints. Additionally, EPDM rubber gaskets typically experience a complex precompression strain state, further complicating the prediction of long-term stress relaxation. Therefore, it is imperative to propose a novel constitutive model that realistically reflects the stress relaxation of rubber with arbitrary precompression strain, providing a reference for the long-term waterproof design of shield tunnels. In this study, the time-varying properties of EPDM rubber at material level were studied in detail. At first, a comprehensive set of accelerated aging tests were conducted on EPDM rubber samples with varying precompression strains. The hardening effect of rubber without precompression and the stress relaxation effect of rubber with precompression were explored. The time-varying law and mechanism governing rubber properties under these two effects were analyzed. Subsequently, a conversion relationship between the EPDM rubber test conditions and the actual service time was established. The predicted hardening coefficient for uncompressed EPDM after 100 years is 1.468, whereas the relaxation coefficient for compressed EPDM is 0.359. Comparative analysis revealed that the compression set index do not consider the beneficial effects of hardening, resulting in a 54.1% overestimation of the design water pressure. Finally, the analytical study on the constitutive model of EPDM rubber material was carried out. The error in compression curve for unaged sample obtained from empirical formulas exceeded three times that of the analytical model, underscoring the need to study time-varying constitutive models. An interpolation method was employed to extend the test curve, leading to the development of a new constitutive model that represents the stress relaxation characteristics of EPDM materials under arbitrary precompression strain states. By combining the proposed constitutive model with the timetemperature conversion relationship, the time-varying expressions of the constitutive parameters for relaxation and hardening effects during the service life were derived. In comparison with existing models, the proposed model demonstrates wider applicability, effectively captures the time-varying characteristics of EPDM materials under arbitrary precompression strains, offering an efficient approach for studying the long-term stress relaxation prediction of rubber gaskets in shield tunnels under complex precompression strain states.

Effects of Steel Fiber Content on Compressive Properties and Constitutive Relation of Ultra-High Performance Shotcrete (UHPSC)

Shotcrete is widely used in civil engineering as a supporting structure. In this paper, the compressive behavior of ultra-high-performance shotcrete (UHPSC) with different steel fiber content by volume (0, 0.5%, 0.75%, 1%, 1.25%, 1.5%) was investigated. The results showed that the failure pattern of UHPSC was changed from brittle failure to ductile failure with the increase in steel fiber content. The compressive strength, peak strain and compressive toughness of UHPSC increased with the increase in steel fiber content, but the elastic modulus and Poisson’s ratio did not change significantly. With content of 1.5% steel fibers, its axial compressive strength, peak strain and compressive strain energy were 122.7 MPa, 3749 με and 0.269 MPa, respectively, increased by 14%, 23.5% and 55.5% compared with those without steel fiber. The peak strain and compressive toughness were higher than that of ultra-high-performance concrete (UHPC), while the elastic modulus of UHPSC was lower than that of UHPC. Based on the experimental data, the relationship between compressive strength, peak strain, compressive toughness and the change in the characteristic value of steel fiber content (λf) were revealed. The uniaxial compressive constitutive model of UHPSC with different steel fiber content was established and reflected the change rule of the shape parameter of α (constitutive model ascending section) and β (constitutive model descending section) with λf. The experimental results were in good agreement with the model calculation results, which can provide theoretical support for the structural design of UHPSC.

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.

Compression Mechanical Properties and Constitutive Model for Soft–Hard Interlayered Rock Mass

The properties of soft–hard interbedded rock masses are significantly impacted by the strength of rock layers and the characteristics of interface surfaces. This study investigates the mechanical properties of soft–hard interlayered rock masses by preparing rock-like specimens with different interface angles. Uniaxial and triaxial compression tests were conducted to examine the compression mechanical characteristics of the specimens. Experimental results demonstrated that in the uniaxial compression tests, the peak strength of the two-layer rock-like specimen exhibits an initial decrease followed by an increase as the interface angle increases. Similarly, the peak strength of the three-layer rock-like specimen also follows a “U-shaped” pattern. The failure of both specimens shifts from tensile failure to shear failure. In the triaxial tests, the strength of the two-layer rock-like specimen initially increases and subsequently decreases as the interface angle increases. In contrast, the intensity of the three-layer rock-like specimen exhibits a decreasing trend, transitioning from shear dilation or tensile failure to shear failure. By utilizing the damage constitutive model to compute the compressive strength of the composite specimen, it was observed that the deviation from the experimental value did not exceed 2.5%, and the overall shape of the curves was in good agreement. Consequently, it is affirmed that the damage constitutive model developed in this study can accurately capture the pre-peak phase of the stress–strain relationship in soft–hard interlayered rock-like specimens, thus providing a valid representation of their mechanical behavior.

Biaxial compressive failure criteria and constitutive model of high-strength geopolymer concrete after high temperature

This paper studies the effect of high temperatures (20℃, 200℃, 400℃, and 600℃) and stress ratios (σ2/σ3) (0.15, 0.3, 0.45, and 0.60) on biaxial compressive strength and strain development patterns of high-strength geopolymer concrete (HGPC). Experimental observations indicate that HGPC exhibits laminar damage similar to ordinary Portland concrete (OPC) before and after exposure to high temperatures, under biaxial compression. Unlike OPC, damage in HGPC initially passes through coarse aggregates at room temperature but shifts predominantly to the aggregate-mortar interface at 600℃. The biaxial compressive strength envelope of HGPC expands with rising temperatures. The increased multiple of biaxial compressive strength (σ3/fm) for HGPC at room temperature rises and then falls with increasing stress ratios, peaking at a stress ratio of 0.45 and surpassing the values for OPC and high-strength concrete (HSC). Before high temperature, the modulus of elasticity of HGPC is higher than that of OPC and decreases with increasing temperature, decreasing by about 45–60% for every 200°C increase, and the reduction is greater than that of OPC. The existing failure criterion is not suitable for HGPC after high temperature, this paper develops a new biaxial compression failure criterion for HGPC before and after high temperature based on Kupfer's criterion, taking into account the effect of temperature. The proposed failure criterion calculation results are well in agreement with the experimental data. A damage constitutive model for HGPC considering the effect of temperature and lateral pressure is also proposed, combining the Weibull distribution model for the ascending branch and a modified empirical model for the descending branch. This combined model effectively predicts the stress-strain relationship of HGPC under various temperature conditions.

Experimental study on the mechanical properties and uniaxial compressive constitutive relationship of sea sand coral concrete

The use of seawater, sea sand and coral to formulate concrete for marine engineering construction is an effective measure for rationally allocating resources and alleviating resource shortages. To promote the engineering application of marine concrete, it is necessary to study the mechanical properties and microstructure of marine concrete. In this study, sea sand coral concrete (SSCC) with strength grades of C20–C40 was prepared, and the compressive and flexural tests were conducted to observe the stress process and damage morphology of the specimens and to establish a constitutive model for SSCC under uniaxial compression. In addition, the microstructures of the SSCC hydration products and interfacial transition zone (ITZ) were observed via X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the damage surface of the SSCC occurred directly through the coral aggregate, and the damage process was sudden and brief. Under uniaxial compression, the trend of the rising section of the stress-strain curve of SSCC with different strength grades are basically the same, but the shape of the descending section vary greatly, and the higher the strength grade is, the steeper the slope of the descending section. Quantitative relationships between compressive strength, elastic modulus, peak strain and peak stress and cube compressive strength were established. Based on the experimental results, a two-stage uniaxial compression constitutive model for SSCC was proposed, and the established constitutive model can effectively predict the stress-strain behavior of SSCC. In addition, the XRD patterns show that the early hydration rate of SSCC is faster than that of ordinary concrete (OC), which leads to a faster early strength development of SSCC. The SEM images show that the coral aggregate binds better to the cement matrix than the crushed gravel aggregate does and that the microstructure of the SSCC is denser than that of OC.

Early mechanical performance of glass fibre-reinforced manufactured sand concrete

The use of manufactured sand as fine aggregate in concrete has been widely adopted in engineering to alleviate the shortage of natural river sand supply. However, there are many factors that affect the properties of manufactured sand concrete (such as the early shrinkage cracking phenomenon is more common than that in natural-sand concrete). In this study, glass fibre was added to manufactured sand concrete to improve its mechanical properties and determine the optimum content of manufactured sand and glass fibre. This study investigated the effects of the replacement rate of manufactured sand and glass fibre dosage on the compressive strength, flexural strength, and shrinkage of concrete. The results show that the optimal replacement ratio of the manufactured sand and ideal glass fibre dosage ranged 60%–80 % and 0.2%–0.3 %, respectively. Concrete exhibited significant improvements in various properties, including 22.97 %, 42.6 %, 7.1 %, and 34.7 % increase in the maximum compressive strength, peak strain, elastic modulus, and flexural strength, respectively. Concrete shrinkage was reduced by 16.1 %. Moreover, a reliable compressive constitutive model for concrete was established, demonstrating high accuracy in predicting the stress-strain relationship of glass-fibre concrete with manufactured sand. The combined utilization of manufactured sand and glass fibres proved to be effective in enhancing the mechanical strength and crack resistance of concrete.

Mechanical properties and damage characteristics of concrete under different atmospheric pressures

The aim of this study was to investigate the mechanical properties and damage characteristics of concrete under different atmospheric pressures (50 kPa, 80 kPa, and 101 kPa). The failure modes, compressive strength, dynamic elastic modulus, stress–strain curve, air pore structure, and acoustic emission (AE) parameters of concrete specimens were evaluated under the different atmospheric pressures. The results showed that as the atmospheric pressure decreased, the concrete damage gradually transitioned from tensile damage to shear damage, the compressive strength and dynamic elastic modulus decreased, and the peak strain increased. The pore structure of the hardened concrete changed, the number of air pores and air content decreased, and the average pore size and pore spacing coefficient increased considerably. Additionally, an analysis of the AE parameters showed that the development pattern of the concrete ringing counts and energy were mostly the same under different atmospheric pressures. The decrease in atmospheric pressure was accompanied by a corresponding gradual decrease in the AE rate of change parameters and cumulative AE parameters, indicating that the concrete crack expansion rate slowed down while the total cracking activity decreased. Moreover, the inverted V-shape of the b-value curve was not obvious, and the peak b-value decreased with decreasing atmospheric pressure. Finally, a combination of the Weibull distribution theory, Lognormal distribution theory, and strain equivalent hypothesis was used to establish a concrete uniaxial compression constitutive model considering atmospheric pressure. The model can reflect the evolution law of the mechanical properties of concrete under uniaxial compression under different atmospheric pressures.

Development of an axial constitutive model for alkali-activated slag recycled concrete–filled circular steel tube columns

Alkali-activated slag recycled concrete (ASRC) effectively utilises slag and construction waste; nevertheless, its poor mechanical properties limit its popularization and application in construction engineering. Therefore, the ASRC–filled circular steel tube column structure (ASRC–FCSTC) is innovatively proposed, and its mechanical properties and constitutive model are studied. The influence of steel ratio and coarse aggregate type, the failure mode, bearing capacity, deformation capacity, and constitutive relationship of core concrete were investigated. The research results show that the failure of ASRC-FCSTC was caused by the shear failure of the core alkali-activated slag recycled concrete, resulting in the overall component failure. In addition, the steel ratio increasing can increase the bearing capacity of ASRC–FCSTC by 47.6-125.4%, and increase the ductility coefficient by 41.6-76.6%. Using recycled coarse aggregate can reduce the bearing capacity of ASRC–FCSTC by 3.3-22.2%. Moreover, the axial compression constitutive model of ASRC–FCSTC core concrete is established considering the effect of steel ratio. Last, the finite element model is established and verified, and the parameter extension analysis is carried out.

Experimental investigation on triaxial mechanical properties of coral coarse aggregate-sea sand seawater concrete

The application of coral coarse aggregate-sea sand seawater concrete (CSSC) in offshore engineering construction is one of the effective measures to realize the rational allocation of resources and alleviate the shortage of resources. In addition, considering that concrete structures in coastal areas may be under triaxial stress, it is necessary to study the triaxial mechanical properties of CSSC. To study the triaxial mechanical properties of CSSC, the effects of aggregate combination and lateral confining pressure on the failure mode, stress-strain curve, yield stress and yield strain of specimens were studied by conventional triaxial tests. The results show that CSSC is more susceptible to the influence of lateral confining pressure. Under the lateral confining pressure of 6 MPa, the crack form transformation and plastic flow appear on the surface of the specimen. Under the lateral confining pressure of 12 MPa, the stress-strain curve appears "stress platform", while the gravel coarse aggregate concrete shows the above changes under the lateral confining pressure of 15 MPa and 24 MPa, respectively. When the lateral confining pressure reaches 15 MPa, the stress-strain curve of CSSC presents a bilinear shape with a second linear branch. With the increase of confining pressure, the damage development rate gradually decreases, and the yield stress and yield strain gradually increase. Finally, the triaxial compression constitutive model of CSSC is established, which can effectively predict the bilinear behavior of the CSSC curve.

Mechanical properties and compressive constitutive model of steel fiber-reinforced geopolymer concrete

Geopolymer concrete is an environmentally friendly material, and the addition of steel fibers can overcome its brittleness and improve its performance, which has broad application prospects. However, there are currently few studies on the comparative analysis of mechanical properties between steel fiber-reinforced geopolymer concrete (SFGPC) and steel fiber-reinforced ordinary Portland concrete (SFOPC), as well as uniaxial compressive constitutive models for SFGPC. Therefore, 144 cubes and 36 prisms were tested for SFGPC and SFOPC. The main variables were the volume content of steel fibers (0 %, 0.5 %, 1 %, 1.5 %, and 2 %), curing age (7 and 28 days), and water-to-binder ratio (0.45, 0.5, and 0.55). The slump, failure pattern, compressive strength, splitting tensile strength, elastic modulus, peak strain, toughness index, and compressive stress−strain curves were obtained. The results indicate that with the increase of steel fiber content, the compressive strength, splitting tensile strength, peak strain, and toughness index of SFGPC increase, while the elastic modulus remains almost unchanged. Compared with the plain geopolymer concrete, the above corresponding indexes of SFGPC with 1 % steel fiber content can be increased by 9.9 %, 20.5 %, 23.3 %, and 52.2 %, respectively. The 7-day compressive and tensile strengths of SFGPC can reach about 80 % of the 28-day strengths. Under the same conditions, SFGPC exhibits higher strength, peak strain, and lower elastic modulus than SFOPC. The scanning electron microscope (SEM) test results show that the geopolymer matrix has a denser structure and a tighter bond with steel fibers than the cement matrix. Based on the plain geopolymer concrete, formulas for mechanical indexes and a uniaxial compressive stress−strain model of SFGPC were proposed.

Compression properties and constitutive model of short glass fiber reinforced poly-ether-ether-ketone (PEEK)

To analyze the deformation behavior of short glass fiber-reinforced poly-ether-ether-ketone (SGFR-PEEK) under various conditions through numerical simulations, it is crucial to construct a constitutive model that can describe its stress–strain behavior over a wide range of strain rates and temperatures. In this study, quasi-static compression tests were conducted on SGFR-PEEK composites with varying mass fractions, and dynamic tests were performed using a Split Hopkinson Pressure Bar to acquire the material's compressive stress–strain response under quasi-static and dynamic conditions. The results indicate that, under compression, the yield stress of SGFR-PEEK composites increases with an augmentation in glass fiber content, rises with increasing strain rate, and decreases with elevated temperature. Based on experimental findings, a modified Johnson–Cook constitutive model was established to characterize the mechanical performance of SGFR-PEEK. In comparison to the traditional Johnson–Cook intrinsic structure model, the modified model takes into account the glass fiber mass fraction as comprehensively as possible and better predicts the material's flow behavior at high strain rates. Finally, this modified constitutive model was implemented in the ABAQUS software using the user-defined subroutine VUMAT to simulate the compression behavior of SGFR-PEEK composites under different loading conditions, and the model was validated. This research provides valuable insights for the practical application of SGFR-PEEK composites in engineering.

Plant fiber foam reinforced with distiller's grains and its static cushioning properties

The non-degradability of plastic foam and limited petroleum resources have caused great damage to the ecological environment of the earth. Here a bio-based foam was fabricated to explore its potential as cushioning packaging materials. Plant fiber foam (PFF) was prepared by foaming via mechanical stirring and oven drying. Sodium alginate (SA) and distiller's grains (DG) were introduced into plant fiber foam as cross-linking agent and filler respectively to enhance fiber bonding and improve the mechanical properties of PFF. Static cushioning properties of PFF were investigated. In addition, the static compression constitutive model of PFF was established and the results showed the model could be used to predict the stress-strain curve of PFF under static compression.

Properties of alkali-activated slag and fly ash blended sea sand concrete exposed to elevated temperature

Alkali-activated slag and fly ash (FA)-blended seawater sea sand concrete (AASC) is a new type of concrete produced without Portland cement or river sand. The advantages of utilising industrial waste and marine resources are that they are not only eco-friendly but cost-saving. This study aimed to investigate the properties of AASC exposed to elevated temperatures. Slag and FA were activated using NaOH and water glass solutions for mixing AASC. Heating and compressive tests were conducted to analyse the thermal and compressive properties of the AASC. The results showed that the AASC with higher FA content (Type II) had fewer flaky structures and more integral interfacial transition zones than the other type of AASC (Type I) after exposure to 600 °C. Type I AASC had better mechanical performance at temperatures below 400 °C but was inferior to Type II AASC beyond 600 °C. A compressive constitutive model was proposed for AASC.

Study of the Design and Mechanical Properties of the Mix Proportion for Desulfurization Gypsum–Fly Ash Flowable Lightweight Soil

In order to solve the global problem of bridge head jumping caused by the insufficient compaction of the roadbed in the transition section of highways and bridges, a desulfurization gypsum–fly ash flowable lightweight soil without vibration, capable of self-compaction, low bulk density, and economic and environmental protection, has been developed. This study selected low-grade cement, industrial waste (fly ash and desulfurization gypsum), and Yellow River silt as the raw materials for the design of the mix ratio of a desulfurization gypsum–fly ash flow-state lightweight soil mix. Through multiple indoor experiments, the influence of cement content, silt content, and the fly ash/desulfurization gypsum quality ratio on its fluidity and mechanical properties was systematically studied. The stress–strain relationship under uniaxial compression was analyzed and the strength formation mechanism was revealed through scanning electron microscopy (SEM). The results show that the mechanical properties of the prepared desulfurization gypsum–fly ash flowable lightweight soil meet the engineering requirements. Increasing both the cement and fly ash content results in the decreased fluidity of the desulfurization gypsum and fluidized fly ash. However, as the mass ratio of fly ash to desulfurization gypsum increases, the fluidity reaches its maximum when the mass ratio of fly ash to desulfurization gypsum is 2:1. Based on the stress–strain relationship test results, a uniaxial compressive constitutive model of the desulfurization gypsum–fly ash flowable lightweight soil was proposed. The model was fitted and analyzed with the test results, and the correlation was greater than 0.96. The high degree of agreement showed that desulfurization gypsum can promote the disintegration of fly ash, thereby increasing the specific surface area. This provides more contact points, promotes the hardening process, and enhances the interlocking force between particles and the formation of cementitious substances, further enhancing strength.

Ultra-lightweight low-carbon LC3 cement composites: Uniaxial mechanical behaviour and constitutive models

The present study aims to characterize the constitutive models of a novel ultra-lightweight low-carbon LC3 cement composite (ULCC-LC3) under monotonic uniaxial compression and tension tests. The compressive stress–strain curves of ULCC-LC3 were obtained based on axial compressive tests. The curve characteristics were analyzed and the data was fitted with the existing concrete compression constitutive model. Modified axial compression constitutive model for ULCC-LC3 was proposed and verified using the independent test data and related data of ULCC in other literatures. The characteristics of tensile stress–strain curves of ULCC-LC3 were also analyzed and studied. Based on existing experimental data, the applicability of the Tetsushi et. al.’s model to this composite was verified. The experimental results show that use of PE fibers can improve the ductility of ULCC-LC3. As compared with normal concrete, ULCC-LC3 exhibits a higher compressive peak strain (over 0.3% for fiber reinforced specimens and over 0.5% for non-fiber reinforced specimens). These findings contribute to the understanding of the mechanical behavior of ULCC-LC3 and provide constitutive models that can be used in numerical simulations and engineering applications to promote the use of this novel ultra-lightweight low-carbon material.

Investigation of Uniaxial Compression Stress–Strain Relationship of Early Age Manufactured Sand Concrete and Its Application

To improve the construction efficiency of the manufactured sand concrete engineering at an early age, the uniaxial compressive stress–strain relationship of C50 manufactured sand concrete is investigated starting at 2 days to 28 days. With the characteristics of the stress–strain relationship, the uniaxial compression constitutive model is determined for the C50 manufactured sand concrete at early age. The influence of age, water-to-binder ratio, and fly ash admixture on the peak stress and peak strain of manufactured sand concrete is analyzed for the parameters of the constitutive model. Results show that the stress–strain curve of manufactured sand concrete is essentially similar to that of ordinary concrete. Via six typical constitutive models, the Sargin model produced the best fitting: its R2 mean is 0.9775, MAE mean is 0.1335, and MSE mean is 0.0175. Considering the influence of different factors, the early age uniaxial compressive constitutive models of manufactured sand concrete were proposed based on the Sargin model. Combined with the on-site construction process of the high pier formwork climb, the finite element analysis was carried out using the proposed early age uniaxial compressive constitutive model. Compared with the measured results of strain near the climbing cone, the error was less than 10% from the simulated value. The findings confirm that the proposed early age uniaxial compressive constitutive model presents great reasonableness for the manufactured sand concrete construction at an early age.

Structural Integrity Assessment of an NEPE Propellant Grain Considering the Tension-Compression Asymmetry in Its Mechanical Property.

In order to investigate the effect of tension-compression asymmetry of propellant mechanical properties on the structural integrity of a Nitrate Ester Plasticized Polyether (NEPE) propellant grain, the unified constitutive equations under tension and compression were established, a new method for grain structural integrity assessment was proposed and the structural integrity of the NEPE propellant grain under the combined axial and transverse overloads was evaluated. The results indicate that the mechanical state of the NEPE propellant grain is in the coexistence of tension and compression under the combined axial and transverse overloads, and the tension and compression regions in the propellant grain is independent of the propellant constitutive behavior. The tension-compression asymmetry of the propellant mechanical properties has a certain impact on its mechanical response. The maximum equivalent stress and strain considering the tension-compression asymmetry falls between that obtained through the tension and compression constitutive model, and is the same as damage coefficient. The safety factor of the NEPE propellant grain considering the tension-compression asymmetry of its mechanical properties is larger than that non-considering, and the traditional method of structural integrity assessment is conservative.

Compressive behavior of steel-polyethylene hybrid fiber reinforced cementitious composite

A hybrid fiber reinforced cementitious composite (HFRCC) was produced by mixing steel fiber (SF) and polyethylene fiber (PE) together in the cement matrix with an appropriate ratio. Under the same PE volume percentage, the effect of various SF aspect ratios (30, 50, 65, 83.3, and 108.3) and volume percentages (0%, 0.3%, 0.6%, and 0.9%) on the compressive behavior of HFRCC was experimentally studied. The results indicated that the aspect ratio and volume percentage of SF had little effect on the elastic modulus of HFRCC. With the addition of SF, the maximum increase of compressive strength and peak strain reached 33.82% and 24.29%, respectively. And the HFRCC presented maximum compressive strength and peak strain when the aspect ratio of SF was 108.3 and the volume percentage was 0.6%. In order to reveal the compressive constitutive relationship of HFRCC, a piecewise function was adopted based on the comparison of existing theory and furthermore in which the fiber reinforcing index, compressive strength, peak strain, and elastic modulus had been introduced. It is concluded that the proposed compressive constitutive model has more agreement with test data.

Simulations of biomass compression-screw feeding using a compressible non-Newtonian constitutive model

There is global interest in the conversion of biomass into sustainable low-carbon-footprint fuels and chemicals as an alternative to non-renewable fossil feedstocks. Feeding biomass solids into pressurized reactors is one of the key steps in biomass conversion. Predicting mechanical failure and energy requirements for this step helps avoid upstream processing bottlenecks and enables efficient operation of a biorefinery. In this work, we developed a predictive computational model for biomass screw feeders that capture the highly viscous, non-Newtonian and compressible behavior of biomass slurries. Biomass compressible behavior is formulated by an equation of state and the non-Newtonian rheology is represented by a density-dependent viscosity model. Experimental data from two compression screw-feeder systems are presented as a validation for our model. Our model successfully predicted the location of the compressed biomass “plug”, biomass flow rate, and the required torque at different operating conditions for the experimental conditions studied in this work.