Compressible Materials Research Articles

Evaluation of the mechanical properties and chemical components of naturally aged glued laminated bamboo

This study experimentally investigated the mechanical properties of aged GLB. The material under investigation was obtained from an outdoor-exposed GLB frame that had been subjected to outdoor exposure for a period of ten years. In-depth discussions were conducted on the mechanical properties and failure modes of the material in tension, compression, and bending. The failure modes were identified as fiber fracture under tension, fiber buckling accompanied by delamination in compression, and a combination of tension failure and transverse shear failure in bending. In comparison to new materials, the tensile strength, compressive strength, and bending strength of aged GLB exhibited a reduction of 5.19–41.2 %, 11.5–26.9 %, and 6.6–40.1 %, respectively. The reduction in strength exhibited considerable variability across the various positions within the aged GLB component cross-section. The greatest reduction in strength was observed in materials located on the upper surface of the component, which were directly subjected to UV radiation and rainwater erosion. Furthermore, Fourier transform infrared (FT-IR) spectroscopy analysis was conducted. The FT-IR spectra demonstrate that the chemical components of bamboo, including cellulose, hemicellulose and lignin, have experienced severe degradation.

Finite Elastic Deformations of Initially Flat Thin Rubber-Like Materials

This contribution aims to derive a nonlinear FE formulation for large elastic deformation of hyperelastic thin rubber-like elastomeric materials. The formulation accounts for isotropic as well as transversely isotropic rubber-like materials. Besides, with the developed formulation, deformation of incompressible as well as compressible materials can be investigated. The formulation is applicable for in-plane and out-of-plane deformation of thin membranes. Several problems are inspected including uniaxial and equibiaxial extension of rubber, axisymmetric deformation of annular sheet, stretching a perforated rubber, extension of an anisotropic rubber, and inflation of an initially-flat circular and a square membrane. The results show very good agreement compared with those reported in the literature. Moreover, this model is able to model the inflation of initially flat membranes which is not possible to be done by commercial software.

Numerical Investigation of Solitary Wave Attenuation by a Vertical Plate-Type Flexible Breakwater Constructed Using Hyperelastic Neo-Hookean Material

This study conducted numerical investigations on solitary wave attenuation by a vertical plate-type flexible breakwater constructed using hyperelastic neo-Hookean material. The wave attenuation performance and elastic behaviors of the flexible breakwater were discussed systematically by considering the effects of three prominent factors: mass coefficient, stiffness coefficient, and Poisson’s ratio. It is indicated that more compressible and flexible materials are beneficial for enhancing efficiency in mitigating solitary wave energy and protecting the structure from damage. In addition, the performance of the hyperelastic neo-Hookean material model was compared with that of a linear elastic isotropic material model coupled with linear and nonlinear geometry analysis (LGEOM and NLGEOM) by evaluating several key targets: wave reflection coefficient, transmission coefficient, horizontal tip displacement, and wave load. Our findings revealed that the hyperelastic neo-Hookean material model showed almost the same predictions as the linear elastic isotropic material model with NLGEOM, but significantly diverged from that with LGEOM. The linear elastic isotropic material model with LGEOM cannot capture the nonlinear variations in structural geometry and stress–strain relationship, resulting in the underestimation and overestimation of horizontal tip displacement under moderate and extreme wave loads, respectively. Moreover, it underestimates the damage inflicted by solitary waves due to inaccurately predicted wave reflection and transmission.

Shock wave formation in radiative plasmas.

The temporal evolution of weak shocks in radiative media is theoretically investigated in this work. The structure of radiative shocks has traditionally been studied in a stationary framework. Their systematic classification is complex because layers of optically thick and thin regions alternate to form a radiatively driven precursor and a temperature-relaxation layer, between which the hydrodynamic shock is embedded. In this work we analyze the formation of weak shocks when two radiative plasmas with different pressures are put in contact. Applying a reductive perturbative method yields a Burgers-type equationthat governs the temporal evolution of the perturbed variables including the radiation field. The conditions upon which optically thick and thin solutions exist have been derived and expressed as a function of the shock strength and Boltzmann number. Below a certain Boltzmann number threshold, weak shocks always become optically thick asymptotically in time, while thin solutions appear as transitory structures. The existence of an optically thin regime is related to the presence of an overdense layer in the compressed material. Scaling laws for the characteristic formation time and shock width are provided for each regime. The theoretical analysis is supported by FLASH simulations, and a comprehensive test case has been designed to benchmark radiative hydrodynamic codes.

Finite deformation modeling of wrinkling in thin magnetoelastic sheets

This paper presents an asymptotic two-dimensional (2D) finite-deformation theory for a thin magnetoelastic sheet starting from a three-dimensional (3D) variational form. This theory is used to model wrinkling phenomena under applied traction and external magnetic field. The resulting 2D potential energy is specialized to an isotropic, in compressible material, and the expressions for material constants, i.e., elasticity tensor, magnetoelastic coupling constant, and permeability, are obtained as a function of the applied magnetic field. The formulation is further simplified assuming reflection symmetry about the mid-surface of the sheet. Strong form of the resulting 2D governing equations are obtained by setting the first variation of potential energy functional to zero. The resulting governing equations are used to analyze wrinkling in a stretched rectangular sheet placed in a uniform magnetic field. Approximate analytical solutions are obtained by linearizing the 2D plate equation for small slopes. The effect of magnetic field and applied stretch on onset of wrinkling and amplitude of wrinkles is studied.

Effect of compressibility on the mechanics of hyperelastic membranes

Elastic membranes are usually studied assuming material incompressibility. However, in several applications they are made of compressible materials such as polymeric foams, hydrogels, and certain kinds of elastomers. Only a few works attempted to incorporate volume changes into membrane problems, but with significant limitations. The models proposed were designed for nearly incompressible materials and lacked a foundation in experimental data, leading to results of limited value. In this work, we investigate the effect of compressibility in membrane problems adopting a consistent model based on the real response of materials to large volume changes. We consider three benchmark problems of nonlinear elasticity: (i) inflation of a circular flat membrane; (ii) inflation of a thin-walled cylindrical tube; (iii) inflation of a thin-walled spherical balloon. Four types of materials divided by increasing degree of compressibility are studied. The results indicate that volumetric deformations have a significant impact on both the limit pressure and the deformed shape. The proposed solutions represent benchmarks for developing new applications of compressible membranes made of polymeric foams and hydrogels, playing an increasingly important role in engineering technologies.

Long-term stress characteristics of a box culvert with a load reduction system using geogrids and EPS under high fill

Laying geogrids and compressible materials, such as expandable polystyrene (EPS), on the tops of culverts under high fill can improve the stability of the fill and reduce the earth pressure on the tops of culverts. The creep of geogrids and compressible materials under high fill affects the stress state of culvert–soil systems. However, the long-term behaviour of culverts with geogrids and EPS is not clear. This paper investigates the long-term behaviour of culvert–soil interactions under high fill, specifically focusing on the creep effects of geogrids and EPS boards. A novel mechanical model for determining the long-term stress characteristics of culverts is proposed based on limit equilibrium theory. A comparison with finite difference simulation results was conducted to validate the proposed model. The findings reveal that the vertical earth pressure on the culvert top gradually transfers to the culvert side, exhibiting a nonlinear decrease over time. Moreover, the horizontal earth pressure on the culvert sidewall exhibits nonlinear growth with time, decreasing incrementally with depth. The maximum horizontal earth pressure on the culvert sidewall increases by 12.5% postconstruction, emphasizing the importance of accounting for the creep effects of geogrids and EPS boards in engineering design to prevent structural issues.

A Critical Review of Methods for Backfill Soil Modulus in Design of Flexible Culverts

Flexible culverts made of corrugated steel or plastic are cost-effective and environmentally friendly alternatives to conventional small road and railway bridges. These structures interact with the backfill by deflecting when subjected to overburden loads, enabling them to utilize the surrounding soil by carrying loads in ring compression. In low soil cover situations, the relationship between bending and backfill soil (stiffness) modulus increasingly influences bearing capacity, and therefore must be considered in design. Backfill soil modulus is a direct result of the execution of the backfilling, and recognized as the most important design parameter because of local uncertainties during construction and material variability. This paper gives a review of some of the existing methods for determining backfill soil modulus. It covers development history, theoretical approximations, aspects of crushed rock materials and their quality, and ease of use in routine design. By applying the methods on different materials and comparing the end results with a compilation of large-scale compression tests and materials from various origins, the performance of the reviewed methods is evaluated. It is found that the reviewed methods have specific drawbacks depending on the actual stress condition and backfill material being applied. In addition, most methods are based on reference laboratory tests carried out on specific and sometimes high-quality materials, and therefore fail to reflect how the quality of rock materials influences the backfill modulus. These shortcomings are used to suggest a new outlook that should be considered in future research on backfill design.

A novel method for determining the resistivity of compressed superconducting materials

The measurement of resistivity in a compressed material within a diamond anvil cell presents significant challenges. The high-pressure experimental setup makes it difficult to directly measure the size changes induced by pressure in the three crystallographic directions of the sample. In this study, we introduce a novel and effective method that addresses these technical challenges. This method is anticipated to offer a valuable foundation for high-pressure investigations on quantum materials, particularly those with anisotropic layered structures.

Finite element analysis of locally strengthened stainless-steel tube under lateral impact loading

In this study, a Finite Element (FE) model of locally strengthened high-strength stainless-steel tube subjected to lateral impact loads is established using LS-DYNA to investigate its dynamic behaviours. The accuracy of the FE results is verified by comparing with the test results. The impact force, bending moment, stress and strain responses as well as the internal energy dissipation histories of the strengthened tube are analysed during the entire impact process. The results indicate that the impact resistance of the strengthened tube is obviously enhanced as compared to hollow stainless-steel tube. Furthermore, parametric studies are conducted to reveal the influence of axial compressive force, impact position, impact velocity and material strength on the impact behaviour of the strengthened tube. The results show that the application of axial compressive force reduced the impact force and increased the deformations of the strengthened tube. The impact resistance of the strengthened tube performed an increasing trend when moving the impact position towards the support and increasing the material strength. In addition, the increase of impact velocity significantly reduced the impact duration. Finally, design recommendations and process were proposed to facilitate the application of locally strengthened tube.

Ground Tire Rubber as a Sustainable Additive: Transforming Desert Sand Behavior

Managing waste tires presents a significant challenge globally, particularly in regions experiencing high temperatures and shortage of landfill sites. This issue is affecting countries like Kuwait, where the abundance of waste tires is a major source of environmental and safety risks, particularly during the intensely hot summer months. This extreme heat has sparked numerous fires, leading to substantial air pollution due to thick black smoke. Given the limited disposal options, recycling waste tires and finding practical applications for ground tire rubber (GTR) is essential. To address the challenge, a comprehensive laboratory testing program was conducted, using locally produced rubber aggregates as an additive to Kuwait's local surface sands. Two new variables were examined namely the size and gradation of the GTR, and the density of the compacted mixes. For this purpose, two different sizes of rubber aggregates, fine and coarse produced locally, were utilized, and the impact of relative compaction on the strength and compressibility of the mixtures was investigated by testing samples compacted to the maximum density and to 95% of the maximum density. The results suggest that combining local surface sands with rubber tire additives results in a lighter, more permeable, and compressible material, contributing significantly to sustainable waste management. With 20% rubber additive the maximum dry density decreased by nearly 20%, and the permeability increased by 1.74–3.11 times and the compression index increased by 6.15 and 3.8 times with fine and coarse rubber respectively. The angle of friction remained unchanged at 36° with the addition of coarse rubber and decreased by 3°–4° with fine rubber. The change in behavior although not an increase in the strength and stiffness, offers a range of suitable practical applications in civil engineering and environmental management, including use as a drainage layer, embankment construction on soft ground, earth fill around retaining walls, an additive in asphalt mixes, and in manufacturing compressible tiles for sports facilities.

Shock compression experiments using the DiPOLE 100-X laser on the high energy density instrument at the European x-ray free electron laser: Quantitative structural analysis of liquid Sn

X-ray free electron laser (XFEL) sources coupled to high-power laser systems offer an avenue to study the structural dynamics of materials at extreme pressures and temperatures. The recent commissioning of the DiPOLE 100-X laser on the high energy density (HED) instrument at the European XFEL represents the state-of-the-art in combining x-ray diffraction with laser compression, allowing for compressed materials to be probed in unprecedented detail. Here, we report quantitative structural measurements of molten Sn compressed to 85(5) GPa and ∼3500 K. The capabilities of the HED instrument enable liquid density measurements with an uncertainty of ∼1% at conditions which are extremely challenging to reach via static compression methods. We discuss best practices for conducting liquid diffraction dynamic compression experiments and the necessary intensity corrections which allow for accurate quantitative analysis. We also provide a polyimide ablation pressure vs input laser energy for the DiPOLE 100-X drive laser which will serve future users of the HED instrument.

Poisson's ratio testing method and multi-factor influence quantification model of asphalt pavement materials

The current standard in China does not specify the standard test method for determining Poisson's ratio, and the Poisson's ratio used in pavement design is often roughly fixed, which can result in large errors in the calculations and analysis of road structure. In this paper, the research on different test methods for Poisson's ratio is carried out and the non-linear characteristics of tensile and compressive Poisson's ratio on pavement materials under different influencing factors are analyzed. The results indicate that the absolute value of the ratio between transverse rebound strain and longitudinal rebound strain under 50% of the maximum destructive load can objectively characterize the mechanical properties of Poisson's ratio, and it is the optimal measurement method for Poisson's ratio in asphalt pavement materials. The Poisson's ratio of two pavement materials both decreases with the increase of loading rate and gradually tends to a constant value. Cement dosage and temperature are the most significant factors affecting the tensile and compressive Poisson's ratio of cement stabilized crushed stone and asphalt mixture, respectively. Specifically, when cement dosage increases by 1%, the Poisson's ratio of cement stabilized crushed stone decreases by approximately 10%, and the temperature has a significant influence on the difference in tension and compression for Poisson's ratio of asphalt mixture (up to 40%). The asphalt content corresponding to the minimum Poisson's ratio is basically consistent with the optimal asphalt content obtained by the Marshall volume method. Based on these, a quantification value-taking model is established of the tensile and compressive Poisson's ratios of typical asphalt pavement materials varying with multiple factors. The research results can serve as a reference for the scientific value-taking of pavement structural design parameters considering the different mechanical characteristics of materials in tension and compression.

Analysis of load-bearing characteristics of bi-modulus composite stiffened plates: Numerical simulation method and large-scale experimental verification

A large number of experiments show that composite materials usually show different modulus properties in tension and compression (bi-modulus). However, for actual composite engineering structures, especially complex models, the numerical simulation calculation is usually based on a single modulus. In order to consider the different modulus characteristics of composite materials in tension and compression, researchers put forward simplified constitutive models of dual-modulus materials. However, these constitutive models have not been verified by a large number of experiments, especially by complex models. In this paper, the GWFMM model is simplified and used to analyze complex structures with different modulus in tension and compression. The experimental results of stiffened plate show that the improved GWFMM model can be used to analyze different modulus of tension and compression of complex stiffened structures. In addition, the influence of elastic modulus ratio in tension and compression under different experimental load conditions is further explored, and the influence law of bending and torsion on structures with bi-modulus is discussed. The relevant conclusions provide reference for the design and optimization of full-scale composite structures in marine engineering.

Mechanical Properties and Failure Behavior of Epoxy Rubber Powder Composites Reinforced with Hollow Beads

In this paper, new epoxy resin/rubber powder/hollow beads three-phase composites were prepared by designing the incorporation of fly ash hollow beads with different mass fractions (5%, 10%, 15%, and 20%) as new reinforcing phases into epoxy resin/rubber powder two-phase composites with 5% mass fraction of carbon black rubber powder. Quasi-static compression tests were conducted at room temperature to test the compressive properties of the oxygen resin/rubber powder/hollow beads composites. Calculate the energy absorption properties and energy absorption efficiency of the composites from the compression curves. Fracture characteristics of compressed material specimens with microscopic morphology were observed by scanning electron microscopy. By systematically analyzing the effect of fly ash hollow beads content on the mechanical properties of epoxy resin/rubber powder/hollow beads three-phase composites, it was found that fly ash hollow beads as reinforcing materials can effectively improve the brittleness and yield strength of epoxy resin/rubber powder as well as the energy-absorbing properties and efficiency of the composites. The energy absorption properties of the epoxy resin/rubber powder/hollow beads composites increased and then decreased with the increase in the mass fraction of fly ash hollow beads. In the epoxy resin/rubber powder/hollow beads composites, the most significant performance was observed when the mass fraction of fly ash was 10%.

Evaluation of arched EPS block and geocell inclusions in trench backfill for protection of buried flexible pipes

This paper presents an experimental investigation examining the novel idea of employing curved expanded-Polystyrene (EPS) blocks that arch around the upper section of buried flexible pipes to reduce the pressures acting on them and hence resulting deformation/deflections. Large-scale testing was performed to examine key performance indicators for reinstated trenches with buried 250-mm diameter plastic pipe (0.75-m invert depth) when subjected to cyclic surface loading simulating vehicular traffic. The real-scale model tests investigated unreinforced and geocell-reinforced trenches with conventional rectangular and differently shaped EPS block inclusions placed above the crown or fitting snugly around the upper section of the buried pipes. Compared to conventional rectangular EPS block, the curved-arched EPS block produced greater reductions in the pressures acting on the buried pipes, resulting in substantially smaller pipe deformation/deflections. The geocell layer overlying the EPS block significantly reduced the pressures bearing on the highly compressible EPS material, thereby reducing its compression and the trench surface settlement. Optimum trench reinstatements incorporated both the geocell layer and a 75-mm thick curved-arched EPS block fitted around the top section of the pipe. Doubling the EPS block thickness produced only modest reductions in the pipe deflections, but significantly increased the trench surface settlement.

Development of the variation-of-elastic-energy-based virtual fields method for parameter identification of incompressible and compressible hyperelastic materials

The virtual fields method (VFM) has played a pivotal role in parameter identification of hyperelastic materials, spanning from rubbers to soft tissues. A key challenge in VFM lies in calculating the internal virtual work, which necessitates the computation of the stress and its conjugate virtual strain. In this study, we introduce a novel theoretical framework for VFM, which directly computes the internal virtual work based on the variation of elastic energy (VEE). The proposed method, namely VEE-VFM, eliminates the calculation of stress and virtual strain, making it remarkably user-friendly compared with the conventional approach. We extend VEE-VFM to both incompressible and compressible hyperelastic materials, including invariant-based and principal stretch-based models. In the end, we demonstrate the accuracy of VEE-VFM and its robustness against noise with numerical experiments.

Stability study of the compressible Mooney-Rivlin hyperelastic model

The unstable behavior of the isotropic, compressible Mooney-Rivlin hyperelastic model is investigated and described. The constitutive equation is parameterized with the help of the ground-state Poisson’s ratio and the dimensionless ratio of the material parameters [Formula: see text] and [Formula: see text]. Transverse stretch solutions are obtained for standard homogeneous loading modes, and the stress solutions are computed numerically for the physically permitted range of the ground-state Poisson’s ratio. We introduce a numerical technique to isolate subdomains with non-unique transverse stretch responses. Our analysis revealed some limitations of the model and allowed us to make critical observations about the strengths and weaknesses of the model. The analyses we present are essential to understand the characteristics of this widely used hyperelastic model. The novel results have important implications for the application of the isotropic, compressible Mooney-Rivlin hyperelastic material model.

Terrene 2.0: Biomaterial composites design & shellular structures development for augmented earthen construction

To transition the construction industry towards sustainable practices, we challenge wasteful methods and non-renewable systems by harnessing local biological materials and augmenting them to describe contemporary forms. Our work enhances the primarily compressive material properties of sand-based compounds to develop a construction method for tension–compression anticlastic shellular structures. We have developed a novel bilayer system with multiscale induced behavior called ChitoSand, made primarily of a sand matrix, incorporating chitosan biopolymer as a microstructural binder, short flax fibers to boost tensile capacity at the mesoscale, and citric acid to increase plasticity, which is then underlaid by a sewn burlap fabric base layer to raise the bending capacity at the macroscale. This produces a fully biodegradable material system that we paired with anticlastic geometry calculations to enhance effective material use and structural form. We then developed an earthen construction workflow that uses reusable pneumatic formwork holding the ChitoSand bilayer composite during hardening in ambient conditions. This research yields a tension–compression system with modern geometry and a minimized environmental footprint.

Electron Microscope Study of the Pressure-Induced Phase Transformation and Microstructure Change of TiO2 Nanocrystals.

Microstructure transformation of materials under compression is crucial to understanding their high-pressure phase transformation. However, direct observation of the microstructure of compressive materials is a considerable challenge, which impedes the understanding of the relations among phase transformation, microstructure, and material properties. In this study, we used transmission Kikuchi diffraction and transmission electron microscopy to intuitively characterize pressure-induced phase transformation and microstructure of TiO2. We observed the changes of twin boundaries with increasing pressure and intermediate phase TiO2-I of anatase transformed into TiO2-II (α-PbO2 phase) for the first time. The following changes occur during this transformation: anatase (diameter of ∼100 nm) → anatase twins 60° along the [110] zone axis → intermediate TiO2-I twins 60° along the [010] zone axis → TiO2-II twins 90° along the [010] zone axis. These results directly reveal the crystallographic relation among these structures, enhancing our understanding of the phase transformation in TiO2 nanocrystals.