Initial Modulus Research Articles

A Study of the Relationship between Polymer Solution Entanglement and Electrospun PCL Fiber Mechanics.

Electrospun fibers range in size from nanometers to micrometers and have a multitude of potential applications that depend upon their morphology and mechanics. In this paper, we investigate the effect of polymer solution entanglement on the mechanical properties of individual electrospun polycaprolactone (PCL) fibers. Multiple concentrations of PCL, a biocompatible polymer, were dissolved in a minimum toxicity solvent composed of acetic acid and formic acid. The number of entanglements per polymer (ne) in solution was calculated using the polymer volume fraction, and the resultant electrospun fiber morphology and mechanics were measured. Consistent electrospinning of smooth fibers was achieved for solutions with ne ranging from 3.8 to 4.9, and the corresponding concentration of 13 g/dL to 17 g/dL PCL. The initial modulus of the resultant fibers did not depend upon polymer entanglement. However, the examination of fiber mechanics at higher strains, performed via lateral force atomic force microscopy (AFM), revealed differences among the fibers formed at various concentrations. Average fiber extensibility increased by 35% as the polymer entanglement number increased from a 3.8 ne solution to a 4.9 ne solution. All PCL fibers displayed strain-hardening behavior. On average, the stress increased with strain to the second power. Therefore, the larger extensibilities at higher ne also led to a more than double increase in fiber strength. Our results support the role of polymer entanglement in the mechanical properties of electrospun fiber at large strains.

Study on dynamic deformation-damage-ignition mechanism of GAP/RDX/TEGDN propellant

ABSTRACT Investigations on high-energy and low-vulnerability propellants can provide a better understanding for improving the operational effectiveness and survivability of strategic and tactical missiles. In the present study, the dynamic compressive mechanical properties and damage-ignition response mechanism of the GAP/RDX/TEGDN (GRT) propellant under high strain rates have been studied using a split Hopkinson pressure bar apparatus and a high-performance high-speed camera. The experimental results suggested that the mechanical properties of the GRT propellant, in terms of yield stress, initial compressive modulus, and ultimate stress, were greatly affected by the loaded strain rate. The true stress-strain curves exhibited an initial linear elasticity region followed by yielding a subsequent strain hardening and strain softening region stage. It has been found that the yield stress and ultimate stress increased with the strain rates. Moreover, at higher strain rates, the impulse increases significantly, leading to earlier and more intense ignition. The critical strain rate and the critical impulse of the GRT propellant are 5000 s−1 and 13.28 N · s, respectively. A judgment basis for GRT propellant ignition is established. Finally, according to the high-speed images and the posttest SEM images, it has been concluded that the dominant ignition mechanism of GRT propellant is flow at the macroscopic level and internal frictional heating at the mesoscopic level.

Polymeric reinforcements for cellularized collagen-based vascular wall models: influence of the scaffold architecture on the mechanical and biological properties.

A previously developed cellularized collagen-based vascular wall model showed promising results in mimicking the biological properties of a native vessel but lacked appropriate mechanical properties. In this work, we aim to improve this collagen-based model by reinforcing it using a tubular polymeric (reinforcement) scaffold. The polymeric reinforcements were fabricated exploiting commercial poly (ε-caprolactone) (PCL), a polymer already used to fabricate other FDA-approved and commercially available devices serving medical applications, through 1) solution electrospinning (SES), 2) 3D printing (3DP) and 3) melt electrowriting (MEW). The non-reinforced cellularized collagen-based model was used as a reference (COL). The effect of the scaffold's architecture on the resulting mechanical and biological properties of the reinforced collagen-based model were evaluated. SEM imaging showed the differences in scaffolds' architecture (fiber alignment, fiber diameter and pore size) at both the micro- and the macrolevel. The polymeric scaffold led to significantly improved mechanical properties for the reinforced collagen-based model (initial elastic moduli of 382.05 ± 132.01kPa, 100.59 ± 31.15kPa and 245.78 ± 33.54kPa, respectively for SES, 3DP and MEW at day 7 of maturation) compared to the non-reinforced collagen-based model (16.63 ± 5.69kPa). Moreover, on day 7, the developed collagen gels showed stresses (for strains between 20% and 55%) in the range of [5-15] kPa for COL, [80-350] kPa for SES, [20-70] kPa for 3DP and [100-190] kPa for MEW. In addition to the effect on the resulting mechanical properties, the polymeric tubes' architecture influenced cell behavior, in terms of proliferation and attachment, along with collagen gel compaction and extracellular matrix protein expression. The MEW reinforcement resulted in a collagen gel compaction similar to the COL reference, whereas 3DP and SES led to thinner and longer collagen gels. Overall, it can be concluded that 1) the selected processing technique influences the scaffolds' architecture, which in turn influences the resulting mechanical and biological properties, and 2) the incorporation of a polymeric reinforcement leads to mechanical properties closely matching those of native arteries.

Assessment of Strength and Deformation Characteristics of High-Strength Concrete in Structures and the Dynamics of Their Changes over Time

Based on the data from numerous production and laboratory tests, an analysis of the actual values of the main standardized strength and deformation characteristics of high-strength concrete of classes B60-B100 was carried out: ultimate resistance to axial compression, initial modulus of elasticity and Poisson’s ratio. It has been established that the values of prismatic strength (Rb) are close to cubic (R), and the ratio between them (prismatic strength coefficient) is not lower than 0.85. A comparison of Rb values with those calculated for limit states of the 1st group according to SP 63.13330.2018 shows that for concrete classes above B70 in the regulatory document they are unreasonably underestimated. The value of the coefficient of variation of high-strength concretes does not exceed 6.5%, which is predetermined by the features of their compositions, which ensure stability of consistency, segregation stability and technological reliability of concrete mixtures. The values of the initial elastic modulus (Eb) exceed the normative ones provided for by SP 63.13330.2018.The dependence of the values of the initial modulus of elasticity of concrete of the same class on the nature of the coarse aggregate has been established. According to experimental data, the elastic modulus can vary in the range of up to 19% depending on the characteristics of the coarse aggregate used. This variability of Eb is consistent with the recommendations of EN 1992-1-1:2004 Eurocode 2, but is not taken into account in SP 63.13330.2018. The time factor affects the change in the values of strength (R and Rb) and elastic modulus (Eb). According to the data obtained, in the period from 28 days to 1.5 years the increase in strength was 15–17%, elastic modulus – 8.8–9.8%. It has been established that changes in these characteristics over time are described by mathematical models and, accordingly, can be predicted depending on the age of concrete. The results obtained indicate that the standardized parameters of SP 63.13330.2018 do not fully take into account the service life of modern high-strength concrete, which makes it necessary to make changes to the specified document.

The Use of CPTU and DMT Methods to Determine Soil Deformation Moduli—Perspectives and Limitations

Abstract The article presents the concept of determining constrained modulus—M0 , initial shear modulus—G0 , Young modulus—E, and rigidity index—IR on the basis of parameters from static penetration tests CPTU (Piezocone Penetration Testing), SCPTU (Seismic Piezocone Penetration Testing) and dilatometer tests DMT (Flat Dilatometer Test), SDMT (Seismic Flat Dilatometer Test). The basis for constructing the empirical relationships between the mentioned modules and parameters from the CPTU and DMT studies was to determine the factors that affect these relationships. The article discusses the impact of the following factors; geological and geotechnical conditions, conditions of recording measurements in CPTU and DMT tests, factors relating to the CPTU and DMT testing methods, factors affecting reference parameters from laboratory tests, factors related to subsoil properties. The basis for obtaining the empirical relationships for determining the analyzed modules and rigidity index were extensive research of the soils of various origins, in Poland. Measurement uncertainties and factors influencing the recorded parameters in the CPTU study were documented by the studies of the Norwegian Geotechnical Institute and the former Department of Geotechnics of the Agricultural University in Poznań. In these studies, penetrometers from several reputable manufacturers were used. The article summarizes the established empirical relationships for individual modules, taking into account the effect of overconsolidation. It also comments on the interrelationship between constrained modulus M0 from CPTU and DMT test for soils in Poland.

Analytical models for stress–strain behaviour of UHPC confined with spiral stirrups

The axial stress–strain models of confined ultra-high performance concrete (UHPC) were important key inputs for analytical programs to predict the full-range loading deformation of confined UHPC. The concrete columns confined with stirrups under axial compression tended to be a failure in shear-compression failure. However, the existing models for evaluating the axial stress–strain models of confined UHPC did not consider the shear-compression failure. In this paper, an experiment on the axial stress–strain behaviour of confined UHPC was presented. The specimens consisted of 75 UHPC with compressive strength up to 155.45 MPa were confined by spiral stirrups. According to test results, a theoretical model for axial stress–strain curves of confined UHPC by considering the shear-compression mechanism of UHPC was developed. In the proposed models, the real lateral stress of stirrups was adopted to calculate the lateral confinement of stirrups, rather than assumed that the stirrups reached the yield strength. In addition, the effects of dowel action of stirrups and longitudinal reinforcement were considered. Furthermore, the prediction models for the compression behaviour indicators of confined UHPC included peak stress, peak strain, initial tangent modulus, residual stress, and residual strain were proposed. By comparing with existing models, the proposed analytical models of axial stress–strain curves of confined UHPC had high accuracy and high stability.

Research on Resilient Modulus Prediction Model and Equivalence Analysis for Polymer Reinforced Subgrade Soil under Dry-Wet Cycle.

The subgrade soil of asphalt pavement is significantly susceptible to changes in moisture content, and therefore many projects introduce polymer-based reinforcement to ensure soil performance. This paper aims to incorporate a variable representing the dry-wet cycle into the prediction model of resilient modulus of polymer reinforced soil. The polymer adopted is a self-developed subgrade soil solidification material consisting of sodium dodecyl sulfate and polyvinyl oxide. The current resilient modulus prediction model is improved, notably involving the effects of the dry-wet cycle. Combined with finite element method (FEM) analysis, the actual stress state of pavement and the coupling effect of dry-wet cycle and vehicle load on the resilient modulus are studied. The deterioration in resilient modulus with the variation in seasonal climate and load response is also investigated. Results show that the deviator stress is negatively correlated with the resilient modulus while the bulk stress has a linearly positive relation. The decreasing rate at low deviator stress is larger than that at the high level. Moreover, the dry-wet cycle can reduce the resilient modulus and the reducing amplitude is the largest at the first dry-wet cycle. FEM analysis shows that the middle position of the subgrade slope has the largest initial resilient modulus with decreasing amplitude in the first year of dry-wet cycles, while the upper position shows a smaller change. The variation in resilient modulus is closely related to the changes in cumulative volumetric water content. Considering that different positions of subgrade bear the external vehicle load, the equivalent resilient modulus is more realistic for guiding the subgrade design.

Mechanistic modeling of fatigue crack growth in asphalt fine aggregate matrix under torsional shear cyclic load

Fatigue crack growth in asphalt pavements under vehicle load may primarily occur within the asphalt fine aggregate matrix (FAM) phase of the mixture. This study aims to predict fatigue crack growth in FAM by developing a mechanistic-based fatigue crack characterization model and fatigue crack growth model under torsional shear cyclic load. Initially, a fatigue crack characterization indicator, fatigue damage density, was derived using principles of torque and dissipated strain energy equivalence. Afterwards, a fatigue crack growth model was established based on the pseudo J-integral Paris’ law. Finally, the viscoelastic damage constitutive model was further constructed by coupling the fatigue crack growth model with a viscoelastic model, which was subsequently implemented in COMSOL Multiphysics. The results show that the fatigue damage density can be determined by the initial shear modulus and phase angle, as well as shear modulus and phase angle under fatigue conditions. Additionally, a logarithmic-linear correlation exists between the fatigue crack growth rate and the dissipated pseudo strain energy rate. The parameters of the fatigue crack growth model exhibit minimal variation across different shear strain levels and temperatures. Overall, the proposed numerical model can effectively simulate damaged torsional shear cyclic tests of FAM.

Determining the Stabilised Subfoudation Soil Deformation Modulus According to the Plate Load Tests and Geotechnical Monitoring Data

Introduction. The subsiding soils, which are widely spread in the south of Russia, create a number of problems and hazards due to the high probability of subfoundations subsidence in case of exceeding the values of initial soil moisture and initial pressure for subsidence. This is an important phenomenon to be considered at all life cycle stages of a building or structure, especially at the stage of design, when the scientifically justified design and technological solutions must be developed to ensure the reliable operation of facilities in the complicated engineering and geological conditions being studied hereby. The present article analyses the acting federal and regional regulatory and technical documentation in the field of buildings and structures design on the subsiding soils. Based on the numerical experiment, the incorrectness of the results sometimes received upon following the normative methodology is shown. A new calculating methodology based on determining the stabilised subfoudation soil deformation modulus according to the plate load tests and geotechnical monitoring data is proposed.Materials and Methods. The research comprised:– analysis of the existing approaches and methodologies for the subfoundations and foundations design on the subsiding soils;– numerical experiments, including calculations according to the normative methodology, which implied variation of the original data of both the initial properties of soils and technological parameters of stabilisation, as well as statistical processing of the results;– analysis of the carried out earlier by the authors geotechnical monitoring results of the buildings built on the stabilized soils and experimental study of the deformation properties using a patented device;– determining the main factors having influence on the design solutions for the subfoudation soils and building foundations strengthening under a complicated set of operational loads and establishing a new dependence of the stabilised soil deformation modulus on the initial soil deformation modulus and percentage of soil reinforcement.Research results. It has been established that the existing methodologies for calculating the stabilised subfoudation soils are not enough precise for determining the forecastable subsidence of buildings and structures, and the obtained design values do not always correspond to the factual deformations of subfoundations and foundations. The dependence of the stabilised subfoudation soil deformation modulus on the initial soil deformation modulus and percentage of soil reinforcement with the cement-sand mortar has been traced. A new calculating methodology has been developed based on determining the stabilised subgrade soil deformation modulus according to the data of the plate load tests using a patented device and geotechnical monitoring.Discussion and conclusion. It has been established that the deformation modulus of the soil mass stabilised by the cementation method depends non-linearly on percentage of soil reinforcement with the cement-sand mortar and the initial soil deformation modulus, and this dependence is described by a second-order surface equation of a general form. It is recommended to apply the discovered dependencies for designing the technological parameters of the subsiding soils stabilisation in the Rostov region conditions.

Skin-Inspired Patterned Hydrogel with Strain-Stiffening Capability for Strain Sensors.

Flexible materials with ionic conductivity and stretchability are indispensable in emerging fields of flexible electronic devices as sensing and protecting layers. However, designing robust sensing materials with skin-like compliance remains challenging because of the contradiction between softness and strength. Herein, inspired by the modulus-contrast hierarchical structure of biological skin, we fabricated a biomimetic hydrogel with strain-stiffening capability by embedding the stiff array of poly(acrylic acid) (PAAc) in the soft polyacrylamide (PAAm) hydrogel. The stress distribution in both stiff and soft domains can be regulated by changing the arrangement of patterns, thus improving the mechanical properties of the patterned hydrogel. As expected, the resulting patterned hydrogel showed its nonlinear mechanical properties, which afforded a high strength of 1.20 MPa while maintaining a low initial Young's modulus of 31.0 kPa. Moreover, the array of PAAc enables the patterned hydrogel to possess protonic conductivity in the absence of additional ionic salts, thus endowing the patterned hydrogel with the ability to serve as a strain sensor for monitoring human motion.

Reliability of Methods for Determination of Stress History Parameters in Soils

Abstract Stress history acquired by any cohesive soil influences, to a large extent, three groups of fundamental properties indispensable in geotechnical design i.e. state of soil, shear strength, and stiffness characteristics. The basic stress history parameter (from which other parameters are derived) determined directly from laboratory tests is a preconsolidation stress σ′ p. Since the first method proposed by Casagrande in 1936, value σ′ p is determined in the oedometer test as a border between overconsolidated (OC) and normally consolidated (NC) zones. Approach based on division between predominantly elastic, (recoverable) strain, and plastic (irrecoverable) strain is a main principle of several methods of σ′ p determination, which have been proposed over the past eighty-six years. Accumulated experiences have revealed that any laboratory procedure based on the oedometer test does not provide realistic value of preconsolidation stress, especially in heavy preconsolidated soils. The major reason for that results from the fact that the mechanism responsible for natural overconsolidation is more complicated than mechanical preloading. Therefore, there is a necessity to reevaluate effectiveness of standard methods and look for another solution of evaluation yield stress σ′ Y in natural soils. This article presents the comparison between σ′ Y determined for various soils with use of standard methods based on conventional oedometer test and yield stress determined on the basis of alternative procedures. The latter are represented by various approaches as e.g. based on SHANSEP procedure or initial shear modulus and others. The most promising among these alternative methods is a new concept based on dilatancy phenomenon that takes place during shearing of a dense soil. The parameter reflecting stress history is derived from pore pressure response and is based on characteristic values of Skempton's parameter A record. Consistency of data concerning stress history parameters profile obtained for deep subsoil on the basis of various methods is shown for comparison.

Full-range stress–strain relationship and fracture model for laser cladding additively manufactured 316L stainless steel sheets

Laser cladding (LC) is being used increasingly in civil engineering owing to its high efficiency and minimal distortion since requiring little heat input; especially for repairing or strengthening damaged metal structures. LC stainless steel sheets are characterised by a rounded stress–strain response, with two “knee” regions and no sharply defined yield point. Such behaviour cannot be accurately represented by using previous stress–strain models. Moreover, determining the true stress–strain curve and toughness coefficient for the fracture model is essential to carry out a non-linear finite element analysis for solving elastoplastic problems. In the present study, one simplified full-range engineering stress–strain model for LC 316L stainless steel sheets is proposed based on the three-stage Hradil model and is validated against the experimental results of thirty tensile coupon tests. The proposed model redefines the second and third stages of the stress–strain curve following the experimental observations. All parameters in this simplified model can be derived directly from only four basic material property parameters: the initial elastic modulus, 0.2 % proof stress, ultimate stress and the strain corresponding to the ultimate stress. For defining the fracture model of LC stainless steel sheets, an average weight method is employed to determine the post-necking true stress–strain curves. The recommended values of the weight factor and toughness coefficient for the LC sheets are also obtained based on the available tensile coupon test results. The comparisons between the experimental force–displacement curves of the tensile coupons and the finite element analysis results using the proposed stress–strain relationship and fracture model for the LC sheets shows both results to be in good agreement. Therefore, the stress–strain relationship and fracture model proposed in this paper is suitable for use in the analytical and numerical modelling of structures having LC 316L stainless steel sheets.

Dynamic behavior of geopolymer stabilized kaolin clay under long-term cyclic loading

Geopolymer has emerged as an alternate cementitious material with a low carbon footprint, as they improve the engineering properties of soft soil without causing a detrimental effect on the environment. This study focuses on developing a combination of geopolymer materials that can fully replace the utilization of traditional binders to stabilize soft soil foundations in geotechnical engineering. Soft kaolin clay was stabilized using ground-granulated blast furnace slag (S) and dolomite (D) as a precursor (P) with combined content of 20% and NaOH: Na2SiO3 ratio of 25:75 as a liquid alkali activator (L) in the geopolymerization process. A series of Unconfined Compressive Strength (UCS) tests were conducted to analyze the influence of various parameters, such as the ratio of S and D, water content of kaolin clay, curing period, and L/P ratio, to select the optimum mix proportions based on strength improvement. This paper also discusses the behavior of geopolymer-stabilized kaolin clay under long-term cyclic loading in stress-controlled conditions. The effect of the S:D ratio, cyclic stress ratio (CSR), curing time, frequency, and confining pressure (CP) on the dynamic shear modulus (G), damping ratio (λ), and degradation index (G/Gmax) were analyzed. The results indicate that the S:D ratio of 16:4 with an L/P ratio of 1, NaOH: Na2SiO3 ratio of 25:75, and water content of liquid limit (LL) cured for 28 days gives the highest UCS value of 1.47 MPa. The initial dynamic shear modulus (Gmax) increases by 60% as the S:D ratio changes from 20:0 to 16:4. The cyclic performance of geopolymer-stabilized kaolin clay in terms of accumulative strain as a function of the number of loading cycles was also enhanced. The findings of the study provide guidance to a better understanding of the long-term dynamic behavior and application of geopolymer-stabilized kaolin clay as a greener approach to ground improvement.

Fabrication, Structural Characteristics, and Properties of Sericin-Coated Wool Nonwoven Fabrics.

Recently, nonwoven fabrics from natural silk have attracted considerable attention for biomedical and cosmetic applications because of their good mechanical properties and cytocompatibility. Although these fabrics can be easily fabricated using the binding character of sericin, the high cost of silk material may restrict its industrial use in certain areas. In this study, sericin was added as a binder to a cheaper material (wool) to prepare wool-based nonwoven fabrics and investigate the effect of the amount of sericin added on the structural characteristics and properties of the wool nonwoven fabric. It was found using SEM that sericin coated the surface of wool fibers and filled the space between them. With an increase in sericin addition, the porosity, moisture regain, and the contact angle of the sericin-coated wool nonwoven fabric decreased. The maximum stress and initial Young's modulus of the nonwoven fabric increased with the increase in sericin amount up to 32.5%, and decreased with a further increase in the amount of sericin. Elongation at the end steadily decreased with the increase in sericin addition. All of the nonwoven fabrics showed good cytocompatibility, which increased with the amount of sericin added. These results indicate that sericin-coated wool-based nonwoven fabrics may be successfully prepared by adding sericin to wool fibers, and that the properties of these fabrics may be diversely controlled by altering the amount of sericin added, making them promising candidates for biomedical and cosmetic applications.

Study on p-y curve of large diameter pile under long-term cyclic loading

The pile foundation used in offshore wind turbine system is located in a complex marine environment and is subjected to various long-term cyclic loads such as wind, wave and current. However, the attenuation effect of long-term cyclic load on seabed soil has not been considered by most of the existing p-y curve calculation models. In order to solve this problem, the finite element numerical model of pile-soil interaction of large diameter single pile foundation of offshore wind turbine is established in this paper. Based on the Stokes second-order wave theory, the time history curve of wave and current loads on piles with different diameters are derived and calculated by programming. Then the soil stiffness attenuati on model subjected to marine cyclic loading is embedded into the finite element model by subroutine. Considering the influence of the number of ocean load cycles on the ultimate soil resistance of the soil around the pile and the initial foundation reaction modulus, the calculation results of different pile diameters and soil depths are analyzed and regressed. Finally, the p-y curve calculation model of large diameter single pile foundation of offshore wind turbine under long-term ocean cyclic load is obtained.

Chitosan/copper sulfide nanoparticles (CS/CuSNPs) hybrid fibers with improved mechanical and photo-thermal conversion properties via tuning CuSNPs' morphological structures

Conventional textiles are inadequate for maintaining warmth in extremely cold conditions. Therefore, the development of photo-thermal fibers for personal thermal management textiles has emerged as an urgent need. Herein, novel chitosan/copper sulfide nanoparticles (CS/CuSNPs) hybrid fibers with photo-thermal function were fabricated successfully. Significantly, our study demonstrated that the tensile and photo-thermal conversation properties of the CS/CuSNPs hybrid fibers could be effectively regulated by altering the CuSNPs` morphological structures. Compared with other CuSNPs (tube-like, sphere-like, and flower-like), the plate-like CuSNPs with smooth surfaces and uniform nanometer size played a significant role by scattering incident light in the fibers as a secondary light source for CuSNPs absorbance. Thus, under IR light irradiation at a power density of 1.0 W/cm2, the surface temperature of CS/0.1 wt% plate-like CuSNPs hybrid fibers sharply increased by 27.6 °C, which was more than 4 times of the pure CS fibers. And the breaking strength and initial modulus of CS/0.1 wt% plate-like CuSNPs hybrid fibers increased by more than 18.37 and 6.88 % compared with the nascent CS fibers. This study develops a novel and effective strategy to tune the photo-thermal and tensile properties of CS hybrid fibers without incorporating more content or additives.

Correlations of sensations of hardness and springiness of agar and gelatin gels with mechanical properties in human participants

ObjectivesIt is unclear which mechanical properties of foods cause the texture sensation in humans. This study aimed to investigate the relationship between unilateral compression measurements and the sensations of hardness and springiness in gels. MethodsThree different concentrations of agar and gelatin gels were prepared by the addition of agar (1%, 2%, and 3%) and gelatin (4%, 8%, and 16%) to water or apple juice. In a stress-rupture test, stress–strain curves were obtained by the application of uniaxial compression with a disc plunger at a compression rate of 10 mm/s. The hardness, springiness, and palatability of the gels were evaluated by 12 healthy volunteers using a visual analog scale. ResultsThe sensation of hardness was positively correlated with the sensation of springiness for the agar and gelatin gels. Palatability decreased as hardness increased for both gels. In terms of mechanical properties, the sensation of hardness was only significantly correlated with the initial elastic modulus, while the sensation of springiness was correlated with the late elastic modulus and other mechanical properties such as fracture strain, time, and stress. ConclusionsThese results suggest that sensations of hardness and springiness are produced in the initial and late stages, respectively, during the food-crushing process using the tongue, palate, and teeth.

An Elementary Formula for the Initial Relaxation Modulus from the Creep Compliance for Asphalt Mixtures.

The conversion between the relaxation modulus and creep compliance is a traditional research topic in viscoelastic materials. Generally, different methods have been used to solve the numerical solution based on convolution theory. However, the initial relaxation modulus (relaxation modulus at t = 0) has been difficult to obtain. This paper aimed to propose a fast calculation method to derive the initial relaxation modulus from the creep compliance. First, three groups of uniaxial static creep tests of asphalt mixtures were conducted to determine the creep compliance of the experimental data. Then, the calculation of the initial relaxation modulus from the creep compliance by three inversion methods (midpoint method, approximate method, and Laplace numerical inversion method) was evaluated. The results indicate that approximate method and Laplace numerical inversion method cannot calculate the initial relaxation modulus value, and the calculation results of the midpoint method can only approach the exact value infinitely, for which calculating the relaxation modulus at 0.0005 s requires 2000 s. The results can only approach the exact value infinitely and take a lot of computing time. Finally, a fast calculation method for the initial relaxation modulus is proposed and verified by Laplace initial value theorem, and this method can directly derive a simple expression for calculating the initial relaxation modulus without requiring computational time. The proposed calculation methods of the initial relaxation modulus for various viscoelastic models were then put forward. The research results provide an effective tool for obtaining the initial relaxation modulus accurately.

Preparation and characterization of polyhydroxyamide composite fibers reinforced with carbon nanotubes—Experiment and computation collaborative approach

AbstractAn experiment‐computation collaborative approach is conducted to investigate and understand the mechanical reinforcement effect of carbon nanotubes (CNTs) on polyhydroxyamide (PHA) composite fibers. The experimental studies provide results of PHA composite fibers with enhanced mechanical properties based on well‐dispersed multi‐walled CNTs (MWCNTs) inside the PHA matrix, suggesting optimal conditions for the experiment‐computation collaborative approach in the polymer/CNT composite systems. For instance, adding MWCNTs up to 2.0 wt% results in an improvement of 48.0% in tensile strength, 36.7% in initial modulus, and 69.9% in breaking strain of the composite fibers. FE‐SEM images show that many MWCNTs are partially exposed or pulled out to the outside of the PHA matrix through the tensile fracture in a very homogeneous dispersion state. In addition, the molecular dynamics (MD) simulation study with a single‐walled CNT (SWCNT) exhibits that the overall displacements of PHA molecules near the CNT surface decrease gradually, which indicates that the PHA molecules form an effective interaction with the CNT. Therefore, it is clear that the excellent interaction between PHA and CNTs, obtained from the results of well‐dispersed CNTs (experiment) and the reduction of the overall displacement of PHA molecules near the CNT surface (computation), is a very important clue to support the improved mechanical characteristics of the PHA fibers reinforced with the CNTs. Moreover, we are confident that the combined experimental‐computational approach used this study will yield valuable insights into the design of composite systems.Highlights Experiment‐computation collaboration reveals enhanced mechanical properties of PHA composite fibers with well‐dispersed CNTs. Addition of MWCNTs up to 2.0 wt% improves tensile strength by 48.0%, initial modulus by 36.7%, and breaking strain by 69.9%. FE‐SEM images demonstrate homogeneous dispersion and partial exposure of MWCNTs in the fractured PHA matrix. MD simulation shows reduced displacements of PHA molecules near SWCNT surface, indicating effective interaction. Combined experimental‐computational approach offers valuable insights for designing composite systems.

Viscoelastic fracture mechanics-based fatigue life model in asphalt-filler composite system

Asphalt-based composites gradually reach the end of their life as the service time increases, which directly leads to fatigue failure of the pavement structure. However, there is currently a lack of a fatigue life model for asphalt-based composites that has a clear physical interpretation. To address this issue, a viscoelastic fracture mechanics-based (VEFM) fatigue life model is proposed to predict the fatigue failure life for asphalt-based composites in this study. The VEFM fatigue life model was established within a viscoelastic fracture mechanics framework and was applied to two types of asphalt-filler composite systems (AFCS). To obtain the model parameters and verify the proposed model, various tests including linear amplitude sweep tests, time sweep tests at low-stress levels and high-stress levels, as well as surface energy tests were conducted on AFCS. The results indicate that the established VEFM fatigue life model can be expressed as a function of the loading level, viscoelastic fracture parameters, initial shear modulus, and surface energy. The initial edge flow of AFCS increases with the temperature and has minimal effect on the fatigue life throughout the fatigue process. A critical fatigue failure point is defined by the curve of damage rate and damage density. The fatigue life of AFCS increases with the temperature while decreasing with the loading level.