Axial Mechanical Properties Research Articles

Axial mechanical properties of small-diameter round timber short columns after exposure to elevated temperatures.

Axial mechanical properties of small-diameter round timber short columns after exposure to elevated temperatures.

Finite Element Analysis of the Axial Mechanical Properties of Piezoelectric Actuator with Tubular Interdigitated Electrodes

We theoretically investigate a new type of piezoelectric actuator with tubular interdigitated electrodes. A partial model is adopted due to the axial symmetry of the actuator, which is divided into non-overlapping opposing electrode pairs on the center plane of the branch electrode. We present a finite element model of actuator and analyze its static-dynamic properties by using the commercially available finite element software ABAQUS. The length-to-diameter ratio of the tubular actuator can be as larger as necessary, so we are more concerned with the axial mechanical properties of the actuator. Thus we studied the influence of the electrode’s shape and structure size on the clamping stress and free strain of the partial models. We also analyzed an ordinary piezoelectric model of the same size. We demonstrated that the partial model displayed significantly improved axial performance over the ordinary one. The axial stress of the partial model can reach 2.75 times that of the ordinary one, and the axial free strain can reach 1.55 times that of the ordinary one. According to the results of the static analysis, appropriate electrodes and structural parameters were selected to establish a tubular actuator model, with which modal and harmonic response analysis were performed. A modal analysis was used to obtain the frequencies and the shapes of the axial vibration. Each pair of electrodes is shunted to a sinusoidal varying voltage. Using the results of the harmonic response analysis, we obtained the actuator’s axial resonance curve.

Molecular dynamics study on axial mechanical properties of calcium silicate hydrate

The axial mechanical properties of calcium silicate hydrate during uniaxial tension or stress have been investigated by molecular dynamic simulations. Based on the classic calcium-silicate-hydrate model, the influence of calcium to silicate ratio and temperature are studied in detail. It demonstrated that calcium silicate hydrate with different Ca/Si ratio have similar stress-strain curves under uniaxial compression, but greatly difference on the uniaxial tension behaviors. The uniaxial tensile properties was affected by temperature that the strain rate in the low-temperature is higher than that in high temperature. The work in this paper reveals the mechanical properties of calcium silicate hydrate at the nanoscale and establishes the foundation explore the failure mechanism of cement or cement-based materials.

Numerical modeling and parametric analysis of grouted connections under axial loading

Abstract With the rapid development of the offshore wind power industry, large-diameter grouted connections (GCs) with high-strength grout have become a developing trend. Previous studies on ordinary-strength and small-scale GCs may not meet current engineering needs. A numerical study was carried out to investigate how the axial mechanical properties of a large-diameter GC that has high-strength grout are influenced by geometric parameters, such as radial stiffness, the height to space ratio (h/s) of shear keys, and the length to diameter ratio (Lg/Dp). The finite element model was verified against the results of the experimental test. The mechanical properties of ultimate bearing capacity, interface transfer strength, ductility, nominal average stress and grout contact pressure distribution are discussed in detail. The results suggest that the increase in radial stiffness can strengthen the axial ultimate bearing capacity and ductility of the GC. Besides, the h/s of the shear keys can affect the ultimate bearing capacity and ductility of GC by influencing the number of diagonal compression struts. Although the Lg/Dp can significantly improve the axial ultimate bearing capacity of GCs, conversely, the interface transfer strength is continuously reduced. The research results can provide technical reference for the design of GCs in the offshore wind turbine industry.

Lightweight, flexible, and multifunctional anisotropic nanocellulose-based aerogels for CO2 adsorption

CO2 adsorption is a promising strategy to reduce costs and energy use for CO2 separation. In this study, we developed CO2 adsorbents based on lightweight and flexible cellulose nanofiber aerogels with monolithic structures prepared via freeze-casting, and cellulose acetate or acetylated cellulose nanocrystals (a-CNCs) were introduced into the aerogels as functional materials using an impregnation method to provide CO2 affinity. The microstructure of the adsorbent was examined using scanning electron microscopy, and compression tests were performed to analyze the mechanical properties of the adsorbents. The CO2 adsorption behavior was studied by recording the adsorption isotherms and performing column breakthrough experiments. The samples showed excellent mechanical performance and had a CO2 adsorption capacity of up to 1.14 mmol/g at 101 kPa and 273 K. Compared to the adsorbent which contains cellulose acetate, the one impregnated with a-CNCs had better CO2 adsorption capacity and axial mechanical properties owing to the building of a nanoscale scaffold on the surface of the adsorbent. Although the CO2 adsorption capacity could be improved further, this paper reports a potential CO2 adsorbent that uses all cellulose-based materials, which is beneficial for the environment from both resource and function perspectives. Moreover, the interesting impregnation process provides a new method to attach functional materials to aerogels, which have potential for use in many other applications.

Axial Mechanical Properties of Timber Columns Subjected to Freeze-Thaw Cycles

The behaviour of timber columns subjected to freeze-thaw cycles under axial compression is presented in this paper. A total of forty specimens, including twenty circular timber columns and twenty square timber columns, were tested under axial compression. The failure modes, ultimate bearing capacity, ductility coefficient, load-displacement curves and load-strain curves were obtained and analyzed. The number of freeze-thaw cycles (from 0 to 80) and the specimens’ height (from 225 mm to 360 mm) were considered as the main parameters. After freeze-thaw cycles, there was no obvious change on the surface of the timber columns. The test results showed that freeze-thaw cycles could reduce the ultimate bearing capacity of the timber columns, and the average reduction of the ultimate bearing capacity of the specimen reached 28%. The ductility coefficient of the square specimens subjected to freeze-thaw cycles almost remains constant compared with that of the square timber columns left untreated. While the ductility coefficient of the circular timber columns increases after freeze-thaw cycles. In addition, based on the extensive experimental analysis, a regression formula is derived to predict the ultimate bearing capacity of the timber columns after being subjected to freeze-thaw cycles, which is proved to be reasonable accurate.

Multi-Scale Modeling and Experimental Study of the Strength of Plain-Woven SiC/SiC Composites

The strength of plain-woven SiC/SiC composites was predicted with the multi-scale method. Firstly, a three-dimensional unit cell was used to characterize the geometric structure of plain-woven SiC/SiC composites. Secondly, the yarns were seen as minicomposites, whose axial mechanical properties were obtained by the shear-lag model, and the fiber defect model was adopted to simulate the failure process of minicomposites. The strength of plain-woven SiC/SiC composites predicted with the multi-scale method is in good agreement with the experimental result. Besides, the effects of heat treatment and load-carrying capacity of broken fiber on the strength of plain-woven SiC/SiC composites were evaluated, and the effect of woven geometry structure was also evaluated.

Axial Compressive Strength Experimental and Numerical Studies of Full-Scale Specimens Simulating GFRP Composite Bushing Column

To study the axial compressive performance of glass fiber-reinforced plastic (GFRP) composite structure, a full-scale axial compression experiment was conducted on GFRP composite bushing (GFRP-CB) column specimens. The axial compressive mechanical properties, failure mode, and load–displacement curves were obtained and analyzed. It is found that brittle fracture occurs in the GFRP-CB column specimens. Diagonal cracks as the main failure mode appear in the upper part of the GFRP pipe. Moreover, the maximum stress in specimens is less than the compressive strength of the GFRP composite material. The steel casing remains in the elastic state during the entire loading process. Based on the strength theory of transversely orthotropic material, the finite element method was used to scrutinize the influence of eccentricity and diameter–thickness ratios on strength of specimens. Numerical results prove that the ultimate bearing capacity of the eccentric compression specimens decreases with the eccentricity ratio. Reduction in diameter–thickness ratio can improve the ultimate bearing capacity of the specimens. As the diameter–thickness ratio decreases by 20%, the ultimate bearing capacity increases by 20%. Finally, an equation for calculating the ultimate bearing capacity of the GFRP-CB column is proposed according to test results. The calculated and test results are fairly consistent, which indicates the effectiveness and accuracy of the proposed equation.

Experimental investigation of bending stiffness of a novel 54m FRP space truss string bridge

Composite truss has the characteristics of light weight, high strength and full play of the axial mechanical properties of the composite components, which can be applied to form long-span bridges, roof structures et al. A novel 54m space truss string bridge made of pultruded GFRP profiles is proposed in this paper based on the composite pre-tightened tooth connection. The proposed space truss string bridge was fabricated, assembled and tested statically, and the load-displacement responses were recorded. The response of the bridge evidenced a sound carrying capacity, the deformation and stiffness of the space truss string bridge meet the requirements and can be used for bridge repair in emergency situations.

Absence of LTBP-3 attenuates the aneurysmal phenotype but not spinal effects on the aorta in Marfan syndrome.

Fibrillin-1 is an elastin-associated glycoprotein that contributes to the long-term fatigue resistance of elastic fibers as well as to the bioavailability of transforming growth factor-beta (TGFβ) in arteries. Altered TGFβ bioavailability and/or signaling have been implicated in aneurysm development in Marfan syndrome (MFS), a multi-system condition resulting from mutations to the gene that encodes fibrillin-1. We recently showed that the absence of the latent transforming growth factor-beta binding protein-3 (LTBP-3) in fibrillin-1-deficient mice attenuates the fragmentation of elastic fibers and focal dilatations that are characteristic of aortic root aneurysms in MFS mice, at least to 12weeks of age. Here, we show further that the absence of LTBP-3 in this MFS mouse model improves the circumferential mechanical properties of the thoracic aorta, which appears to be fundamental in preventing or significantly delaying aneurysm development. Yet, a spinal deformity either remains or is exacerbated in the absence of LTBP-3 and seems to adversely affect the axial mechanical properties of the thoracic aorta, thus decreasing overall vascular function despite the absence of aneurysmal dilatation. Importantly, because of the smaller size of mice lacking LTBP-3, allometric scaling facilitates proper interpretation of aortic dimensions and thus the clinical phenotype. While this study demonstrates that LTBP-3/TGFβ directly affects the biomechanical function of the thoracic aorta, it highlights that spinal deformities in MFS might indirectly and adversely affect the overall aortic phenotype. There is a need, therefore, to consider together the vascular and skeletal effects in this syndromic disease.

Investigation of Elastic Parameters of Three-Dimensional Full Five-Directional Braided Composite Materials

The aim of this paper is to investigate the material constants of three-dimensional full five-directional (3Df5d) braided composites. Based on the yarn deformation mode, the relation between material constants and braiding parameters is systematically deduced. The technological factor λ is proposed using the energy theory with consideration of the cross section and lateral deformation of axial yarns after solidification. Longitudinal moduli of all the unit cells are modified, and analytical solutions regarding λ are eventually obtained with volume average method. The results show that the elastic properties of this material are strongly designable and closely related to internal braiding angle and fiber volume fraction; the longitudinal modulus highly depends on λ which ranges from 1.3 to 2 according to technological level and it coincides well with the experimental results when λ takes 1.3; increased λ can guarantee better geometrical morphology of axial yarns and thus enhance the axial mechanical properties; the longitudinal modulus can still be improved by about 20%, relative to the test data, which seems unrelated to the braiding parameters. The developed methodology performs well in predicting the material constants of 3Df5d braided composites, which can be of certain significance for other textile materials.

Axial mechanical and structural characterization of keratoconus corneas

PurposePrevious studies indicate that there is an axial gradient of collagen lamellar branching and anastomosing leading to regional differences in corneal tissue stiffness that may control corneal shape. To further test this hypothesis we have measured the axial material stiffness and quantified the collagen lamellar complexity in ectatic and mechanically weakened keratoconus corneas (KC). MethodsAcoustic radiation force elastic microscopy (ARFEM) was used to probe the axial mechanical properties of the cone region of three donor KC buttons. 3 Dimensional second harmonic generation microscopy (3D-SHG) was used to qualitatively evaluate lamellar organization in 3 kC buttons and quantitatively measure lamellar branching point density (BPD) in a separate KC button that had been treated with epikeratophakia (Epi-KP). ResultsThe mean elastic modulus for the KC corneas was 1.67 ± 0.44 kPa anteriorly and 0.970 ± 0.30 kPa posteriorly, substantially below that previously measured for normal human cornea. 3D-SHG of KC buttons showed a simplified collagen lamellar structure lacking noticeable angled lamellae in the region of the cone. BPD in the anterior, posterior, central and paracentral regions of the KC cornea were significantly lower than in the overlying Epi-KP lenticule. Additionally, BPD in the cone region was significantly lower than the adjacent paracentral region in the KC button. ConclusionsThe KC cornea exhibits an axial gradient of mechanical stiffness and a BPD that appears substantially lower in the cone region compared to normal cornea. The findings reinforce the hypothesis that collagen architecture may control corneal mechanical stiffness and hence corneal shape.

Study on the Mechanical Property of 20Cr13 Stainless Steel Barrel Processed by Cold Radial Forging

The barrel is a key part of automatic weapon. And the cold radial forging progress is a new technology for manufacturing the barrels. It will introduce some changes of the material, such as increased strength, decreased plasticity and introduction of anisotropic mechanical property. It can affect the service performance, so it is necessary to study the difference of tangential and axial mechanical properties of barrel blank and forged barrel. This paper focuses on the research of 20Cr13 stainless steel barrel. The mechanical properties of barrel blank and forged barrel are measured by the tensile, compression and bulging test. And the hardness is measured by Vickers hardness tester. The structural change of 20Cr13 stainless steel also has been observed by metalloscope in the metallographic experiment. It reveals the influence of the cold radial forging progress on the mechanical properties of 20Cr13 stainless steel barrel. And it also provides the reference data of the cold radial forging progress of 20Cr13 stainless steel.

Measurement of the axial and circumferential mechanical properties of rat skin tissue at different anatomical locations.

Skin tissue is not only responsible for thermoregulation but also for protecting the human body from mechanical, bacterial, and viral insults. The mechanical properties of skin tissue may vary according to the anatomical locations in the body. However, the linear elastic and nonlinear hyperelastic mechanical properties of the skin in different anatomical regions and at different loading directions (axial and circumferential) so far have not been determined. In this study, the mechanical properties during tension of the rat abdomen and back were calculated at different loading directions using linear elastic and nonlinear hyperelastic material models. The skin samples were subjected to a series of tensile tests. The elastic modulus and maximum stress of the skin tissues were measured before the incidence of failure. The nonlinear mechanical behavior of the skin tissues was also computationally investigated through a constitutive equation. Hyperelastic strain energy density function was calibrated using the experimental data. The results revealed the anisotropic mechanical behavior of the abdomen and the isotropic mechanical response of the back skin. The highest elastic modulus was observed in the abdomen skin under the axial direction (10 MPa), while the lowest one was seen in the back skin under axial loading (5 MPa). The Mooney-Rivlin material model closely addressed the nonlinear mechanical behavior of the skin at different loading directions, which can be implemented in the future biomechanical models of skin tissue. The results might have implications not only for understanding of the isotropic and anisotropic mechanical behavior of skin tissue at different anatomical locations but also for providing more information for a diversity of disciplines, including dermatology, cosmetics industry, clinical decision making, and clinical intervention.

Axial strain localization of CuCrZr tubes during manufacturing of ITER-like mono-block W/Cu components using HIP

Two forms of axial strain localization of CuCrZr tubes, i.e., cracking and denting, were observed during the manufacturing of ITER-like mono-block W/Cu components for EAST employing hot isostatic pressing (HIP). Microscopic investigations indicate that the occurrence of axial strain localization correlates to the heavily deformed Cu grains and elongated Cr-rich precipitates as well as highly anisotropic microstructures, which impair the circumferential ductility. Annealing the as-received tubes at 600°C alleviates cracking due to partial recrystallization of Cu grains. However, the annealed tubes are still sensitive to wall thinning (caused by non-uniform polishing or tube bending), which results in denting. Denting may cause bonding flaws at CuCrZr/Cu interfaces and the underlying mechanisms are discussed. To some extent, denting seems do not affect the high heat flux performance of components. In this paper, we demonstrate that testing only the axial mechanical properties is not enough for manufacturers who use HIP or hot radial pressing technologies, especially for those anisotropic tubes.

Research on the Influence of Fiber Web to the Axial Compression Performance of EPS Composite Insulation Wallboard

To improve the axial compression mechanical properties of the EPS particle-EPS board composite insulation wallboard, added fiber web at different levels of it, got the best arrangement to improve the performance of axial compression through the test.

Characterization of evolving biomechanical properties of tissue engineered vascular grafts in the arterial circulation

We used a murine model to assess the evolving biomechanical properties of tissue engineered vascular grafts (TEVGs) implanted in the arterial circulation. The initial polymeric tubular scaffold was fabricated from poly(lactic acid)(PLA) and coated with a 50:50 copolymer of poly(caprolactone) and poly(lactic acid)(P[PC/LA]). Following seeding with syngeneic bone marrow derived mononuclear cells, TEVGs (n=50) were implanted as aortic interposition grafts in wild-type mice and monitored serially using ultrasound. A custom biaxial mechanical testing device was used to quantify the in vitro circumferential and axial mechanical properties of grafts explanted at 3 or 7 months. At both times, TEVGs were much stiffer than native tissue in both directions. Repeated mechanical testing of some TEVGs treated with elastase or collagenase suggested that elastin did not contribute significantly to the overall stiffness whereas collagen did contribute. Traditional histology and immunostaining revealed smooth muscle cell layers, significant collagen deposition, and increasing elastin production in addition to considerable scaffold at both 3 and 7 months, which likely dominated the high stiffness seen in mechanical testing. These results suggest that PLA has inadequate in vivo degradation, which impairs cell-mediated development of vascular neotissue having properties closer to native arteries. Assessing contributions of individual components, such as elastin and collagen, to the developing neovessel is needed to guide computational modeling that may help to optimize the design of the TEVG.

Mechanical Properties of Trabecular Bone through Compression and Combined Compression-Torsion Test: A Comparative Study

In realistic service of life, trabecular bone is subjected to multiaxial stress histories during physiological routine activities thus investigation on the mechanical environment is important to evaluate the mechanistic aspects of bone failure in trauma. This study attempts to compare the material properties of trabecular bone with regard to mechanical properties in axial compression and combined compression-torsion. How superimposed axial compression and torsion loads would alter the axial mechanical properties is explained. Shear loading demonstrates tenfold reduction in modulus and 27% reduction in yield strength of bone in comparison to the properties of bone in pure compression. This condition shows that superimposed torsional loading is possible to accelerate bone yielding.

Theoretical study of soft-to-hard transition of copper-filled carbon nanotubes

Copper-filled carbon nanotubes (Cu@CNTs) have been extensively reported to possess remarkable axial mechanical properties, but little is known about their radial mechanical properties. In this study, we perform the molecular dynamics (MD) simulations to systematically investigate the radial compression of Cu@CNTs. The results indicate that Cu@CNTs possess very high radial strength. The force–strain curves show several soft-to-hard transitions during the compression. The radial strengths of the empty CNTs and copper-filled double-walled carbon nanotubes (Cu@DWCNTs) have been calculated for comparison. Effects of tube length, diameter, chirality, and the number of Cu atoms on the radial mechanical properties are also discussed. This study may provide motivation to explore new applications of metal-filled CNTs.

The hierarchical structure and properties of multifunctional carbon nanotube fibre composites

The axial mechanical, electrical and thermal properties of carbon nanotubes (CNTs) can be exploited macroscopically by assembling them parallel to each other into a fibre during their synthesis by chemical vapour deposition. Multifunctional composites with high volume fraction of CNT fibres are then made by direct polymer infiltration of an array of aligned fibres. The fibres have a very high surface area, causing the polymer to infiltrate them and resulting in a hierarchical composite structure. The electrical and thermal conductivities of CNT/epoxy composites are shown to be superior to those of equivalent specimens with T300 carbon fibre (CF) which is widely used in industry. From measurements of longitudinal coefficient of thermal expansion (CTE) of the composites we show that the CTE of CNT fibres is approximately −1.6 × 10 −6 K −1, similar to in-plane graphite. The combination of electrical, thermal and mechanical properties of CNT fibre composites demonstrates their potential for multifunctionality.