Compression Mode Research Articles

Flexural behavior of warp knitted textile reinforced concrete impregnated with cementitious binder

Textile reinforced concrete is a novel and high performance material which is gaining popularity in the recent days due to its high potential to effectively improve the strength and durability of concrete structures. Owing to absence of coarse aggregate and presence of high cement paste content, TRC has properties that are different from conventional concrete. In this paper, performance of three different types of binders ie., Organic binder, Inorganic Geopolymer binder and epoxy binders for compressive and split tensile strengths was presented and were compared to assess their effectiveness in enhancing properties by testing 12 mortar cubes of size 70.6 mm and 6 mortar cylinders of size 75 × 150 mm. The efficaciousness of weft insertion warp-knitted textile fabrics of ARG and Basalt on the Compressive strength, flexural strength, ductility, toughness, and failure modes were evaluated experimentally by investigations carried out on 4 RCC beams. The effect of the thickness of Textile reinforcement is also studied by using textile layers of thicknesses of 5, 10, and 15 mm. The results indicated that application of basalt textiles fabric using cementitious binder exhibit higher strength and ductility. Basalt textile is more preferable due to its eco-friendly properties. The experimental findings are validated through analytical equations, ensuring the reliability of the study.

Tribological and braking performance study of additive-based MR fluids in shear and hybrid mode using MR drum brake

The braking performance of magnetorheological (MR) brake can be improved by utilizing hybrid mode of operation of MR fluid in brake and by enhancing the rheological properties of MR fluid. This work presents an MR drum brake, which can operate in shear mode as well as in shear plus compression mode, i.e., hybrid mode. The use of compression mode increases the interactions of iron particles with the contacting surface of the rotor and stator, which affects the gap of the MR zone, which is one of the performance parameters for MR brakes. Hence, the presented work attempted to prepare an MR fluid that offers not only good tribological properties as well as best braking performance with MR drum brake. So, MR fluids have been prepared using the same percentages of different additives such as graphite flakes, MWCNTs, and zinc oxide. The rheological, tribological, and braking performance of these prepared MR fluids have been studied using a rheometer, tribometer, and brake inertia dynamometer, respectively. The study found that zinc oxide-based MR fluid is the most suitable MR fluid for the presented MR drum brake in terms of braking performance and tribological aspects.

4D printing of porous PLA-TPU structures: effect of applied deformation, loading mode and infill pattern on the shape memory performance

For the first time, the synergy of shape memory polymer (SMP) blending, 4D printing, and cold programming (CP) are investigated for improving the functionality of the shape memory effect (SME), increasing medical applications of porous structures, direct programming, and removing current limitations. Porous PLA-TPU structures with different printing patterns and applied deformation were CPed under constrained and non-constrained compression modes at room temperature and were recovered in the rubbery phase. The shape fixity and shape recovery ratios were calculated and the cross-section morphology was examined with scanning electron microscopy (SEM). The shape fixity values were in the range of 39.75%–71.27%, while almost complete shape recovery ratios (100%) were observed for all porous samples. Low shape fixity ratios can be justified due to the existence of two steps of spring-back and structure relaxation after unloading in cold programming, resulting from elastic and viscoelastic behavior. The glass transition temperature of the PLA-TPU blend was 69 °C and shifted to raw materials, indicating the possibility of some interaction between the two components. SEM images showed the uniform distribution of TPU particles and matrix-droplet morphology in the PLA-TPU blend. After printing, TPU droplets were stretched and the sea-island morphology was observed in some segments.

Piezo-tribo-electric nanogenerator based on BCZT/MCNTs/PDMS piezoelectric composite for compressive energy harvesting

BackgroundThis work has developed a novel piezo-tribo-electric nanogenerator (P-TENG) that is capable of converting mechanical energy into electrical energy when operating in compressive mode. MethodsAn arch-shaped P-TENG device was formed using an optimal piezoelectric polymer composite, which was fabricated using a polydimethylsiloxane (PDMS) matrix that was modified with piezoelectric (Ba0.85Ca0.15) (Ti0.90Zr0.10)O3 (BCZT) ceramic particles and electrically conductive multi-walled carbon nanotubes (MCNTs). A high filler loading of BCZT (40, 50, 60 wt%) and 3 wt% of MCNTs was formed into a 0–3 connectivity composite. ResultsThe P-TENG device containing 50 wt% BCZT exhibited the highest electrical output (VOC ∼ 39.7 V, ISC ∼ 1.9 µA, and maximum power ∼ 157.7 µW), compared to the other composites, when subjected to an alternating compressive load of 500 N at a 1 Hz frequency. ConclusionsThis research provides new composite formulations for elastomeric-based energy generators that are responsive to low frequency mechanical oscillations.

Experimental and numerical analysis of the Microstructure and mechanical properties of unidirectional glass fiber reinforced epoxy composites

This paper proposes a numerical model to predict the pattern and features of the fracture surface and to understand the mechanisms and cause of the failure. Various fiber orientations of 0°, 90°, 0°/90° and ± 45° were utilized in the production of unidirectional glass-fiber-reinforced epoxy composites via the vacuum bagging technique. The mechanical properties of the manufactured composites were evaluated by measuring parameters including tensile strength, compressive strength, flexural strength and interlaminar shear strength. High-resolution scanning electron microscopy was used to examine the mechanisms of fracture in laminates. The mechanical properties of the composite material were found to be considerably improved when a unidirectional 0° fiber orientation was used, as compared to other fiber orientations. This was true for tensile, compressive, flexural and interlaminar shear loading modes. The composite laminates demonstrated several modes of breaking, including fibers pulling away from the matrix, holes in the matrix and river flow lines, depending on the direction of the fibers. The outcomes of the numerical simulation demonstrate a high level of fidelity with experimental findings. This study provides a valuable reference for predicting numerical analysis of the microstructure and mechanical properties.

A novel constitutive model for the concrete face slab of a CFRD and the numerical simulation of its seismic behavior

AbstractWith the rising demand for hydropower energy, China has built numerous concrete‐faced rockfill dams (CFRDs) with considerable heights. The potential failure pattern of the concrete face slab is the key to the safety of the anti‐seepage system. However, engineers commonly employ an elastic relationship to model the concrete face slab for simplicity, which induces inaccurate estimation of the face slab's stresses, especially under seismic conditions. On the other hand, the existing elastoplastic models for concrete often require complex derivation of the necessary formula and thus are difficult to apply to finite element (FE) analysis. Under the comprehensive action of the upstream water, supporting rockfill, and surrounding mountains, the damage mode of the quasibrittle concrete slab is not a tensile mode but a compressive shearing mode. Therefore, it is urgent to establish an elastoplastic model that is adapted to the actual working environment of the slab and easy to apply. To this end, a generalized plasticity model is developed within the phenomenology modeling concept, which is validated at both the experimental level and application level. The results indicate that three‐dimensional stress‒strain behaviors, such as the strength nonlinearity, prepeak dilatancy, and postpeak softening, can be effectively captured. In addition, the seismic characteristics of a 200‐m high CFRD are numerically investigated. The findings show that the slab's stress accumulation can be reflected during the earthquake and that the final stress distribution conforms to the field observations. The conclusions of this paper provide a reliable reference for the seismic resistance design of CFRDs.

Self-repair of magnetically active composite sample in extreme compression test

A sample of a magnetically active composite with ferromagnetic fillers is studied. It is known that magnetoactive composites are of interest for use in a number of fields of science and technology. The characteristics of changes in the properties of magnetoactive composites with ferromagnetic fillers in compression tests under repeated loading are poorly studied. The study in different, wide force modes of compression to establish the conditions of self-restoration of the material shape is of practical and scientific interest for further use of the tested material. The machine on which the tests are carried out allows loading and studying the character of the sample behavior from small to extreme compression forces. The possibility of preserving the shape memory effect of the test material after a long period between the first and repeated test and under the condition of exceeding the compression force of the sample almost three times compared to the first test is determined. The dependence of the change in the magnitudes of the sample deformations on the compression load is determined. The ranges of non-linear character of variation of the sample deformations from the compression force starting practically from 60% of the value of its initial deformation are shown. The sample tested under extreme compression of up to 30 kN, as well as in the initial test, demonstrated self-recovery (shape memory effect). Thus, the effect of reversible deformation after extreme loads, which exceeded the initial ones by 3 times, was confirmed.

Design, development, and performance analysis of plate-plate hybrid magneto rheometer considering uniform radial magnetic flux

The current study presents a magnetic numerical simulation of a plate-plate magnetorheometer using the finite-element method. In this study, a magnetorheometer with the least number of coil turns has been proposed and developed to obtain a high and consistent magnetic flux density (0.68 T at 3A) along the radius of the magnetorheological fluid (MRF) zone. The possibility of radial migration of MRF is eliminated by the lack of a magnetic flux gradient along the MRF zone’s radius. After comparing the temperature rise in the magnetorheometer caused by resistive and viscous heating in the simulation and the experiment, it has been found that the temperature rise has a negligible effect on the MR fluid. When we conducted studies in hybrid mode—that is, shear plus compression mode—we found that, under the same operating conditions, the shear stress was significantly higher compared to when we only used shear mode. In the combined shear plus compression mode, it has been observed that the effects of particle concentration and compression velocity have a significant impact on the shear stress value.

Failure behavior of steel dual-angle with cruciform welding filler plates under compression

This paper focuses on the failure behavior of steel dual-angle with cruciform welding filler plates (DA-CWP) under compression. A total of three DA-CWP specimens were fabricated and tested under axial compression, where different slenderness ratios (i.e., 45, 60, 75) were considered for comparison. The failure performance was experimentally investigated from different perspectives, such as failure mode, ultimate capacity and strain development. Subsequently, numerical simulation was performed to further reveal the effect of slenderness ratio and filler plate type on the failure behavior of DA-CWP. Finally, A theoretical method to distinguish the compressive failure mode of DA-CWP was proposed, and the bending-torsion transition slenderness ratio calculated by theoretical method was compared with the one from simulation for verification. The results demonstrate that the failure mode of DA-CWP changes from torsion to bending as the slenderness ratio increases, gradually decreasing its ultimate capacity. Due to the lower torsion stiffness of steel dual-angle with alternate plates (DA-AP), the torsion instability is more prone to occur for DA-AP, resulting in larger deformations of DA-AP compared to DA-CWP under identical compression. The theoretical method proposed in this study provides a good prediction for the bending-torsion transition slenderness ratio of DA-CWP under axial compression, which can provide reference for ultimate capacity design.

Linear stability of a compressible flow in a channel

Summary Modal instabilities in a compressible flow through a channel at high Reynolds numbers are studied for three-dimensional (3D) perturbations. In addition to the Tollmien–Schlichting (TS) mode, there exist compressible modes in a channel flow that do not have a counterpart in the incompressible limit. The stability characteristics of these compressible modes, obtained through numerical calculations, are compared with boundary layer and Couette flows that have been previously studied. The dominant compressible instabilities in a channel flow are shown to be viscous in nature, in contrast to compressible boundary layer modes. For general compressible bounded-domain flows, a necessary condition for the existence of neutral modes in the inviscid limit is obtained, and this criterion is used to determine critical Mach numbers below which the compressible modes remain stable. This criterion also delineates a range of wave-angles which could go unstable at a specified Mach number. Asymptotic analysis is carried out for the lower and upper branches of the stability curve in the limit of high Reynolds number for both the T-S and the compressible modes. A common set of relations are identified for the scaling exponents, and the leading order eigenvalues for the unstable modes are obtained through an adjoint-based procedure. The asymptotic analysis shows that the stability boundaries for 3D perturbations at high Reynolds numbers can be calculated from the strain rate and the temperature of the base flow at the wall.

Axial and radial reversibility and energy absorption behaviors of braided shape memory composite thin-walled tubes

Braided shape memory polymer composites (SMPCs), which integrate braided structures with shape memory polymers, are well-known for their superior mechanical properties, reversible deformation, and recovery capabilities. This study focused on exploring the reusable energy absorption capacity of intelligent braided SMPC tubes. The effects of braiding structure on compression modes, mechanical properties, energy absorption, shape memory performance, and repeatability under axial and radial compression have been comprehensively investigated. The results show that SMPC tubes have a shape recovery ratio exceeding 94 % after four cycles. As the number of compressions increased, both the mechanical and energy absorption properties decreased, particularly during the first compression. Higher energy absorption capacity has been observed in SMPC tubes with larger braiding angles, up to 32.51 J, 2.3 times that of pure TPU tubes. These findings offer potential approaches for the development of high-performance reusable protective devices and lightweight intelligent structures.

Experimental study on the size effect and anisotropy in mechanical properties of fractured rock mass based on 3D printing

The size effect and anisotropy of fractured rock mass mechanical parameters are difficult problems to solve in the field of engineering. This study taken full advantage of sand 3D printing technology to batch-reproduce complex structures and prepare rock-like specimens with different sizes and rotation directions. The size effect and anisotropy of the fractured rock mass were investigated. Digital image correlation was used to conduct noncontact full-field observations of the specimen. The results showed that the sand 3D printing specimens have the advantages of high precision and brittleness and can reproduce the deformations and failure processes of natural rock. The compressive strength and failure mode of the fractured rock have significant size effect characteristics. Assessing the size effect on the compressive strength of the specimen, 100 × 100 mm is the mechanical representative elementary volume (mREV) scale. The compressive strength and failure mode of the fractured rock under the mREV scale show obvious anisotropy. Based on the size effect of fracture density, 80 × 80 mm was identified as the geometric representative elementary volume (gREV) scale. The gREV scale was smaller than and close to the mREV scale was found. In addition, the differentiation rate of standard deviation (DRSD) is defined to provide information on the dispersion of the strain field and the precursor information of crack initiation during the deformation and fracture of the rock mass. This study provides a new method for laboratory experimental studies on the size effect and anisotropy of complex fractured rock masses from the perspective of 3D printing.

Influence of Different Factors on Permanent Deformation of Hot Asphalt Concrete Mixtures

Abstract The performance of flexible pavements is significantly impacted by the permanent deformation (rutting) of asphalt pavements. The research aims was to evaluate the permanent deformation of asphalt mixtures under different conditions. To achieve this aim, 108 cylindrical specimens have been prepared and tested under repeated loading in uniaxial compression mode. Five factors were considered in this research. They include testing temperature, loading conditions (stress level and duration), and mixture properties (bitumen type and content). The permanent deformation is evaluated in term of the following parameters, permanent micro strain εp, resilient micro strain εr, initial permanent strain (intercept, a), accumulation rate of permanent deformation (slope, b), rate of decrease in permanent deformation α and constant of proportionality between permanent and elastic strains Mu. The test results showed that the εp and a are increased as the testing temperature increased. In addition, the εp value for load duration of 0.4 s is 1.64 times the value for 0.1 s. Finally, the findings showed that the resilient response of the material is comparatively more sensitive to bitumen content than the plastic response. Furthermore, the rutting resistance is highly affected by the variables considered in this research.

3D Printable Self‐Sensing Magnetorheological Elastomer

AbstractMagnetorheological elastomers (MREs) are a category of smart materials composed of a magnetic powder dispersed in an elastomeric matrix. They are characterized by the ability to change their mechanical properties when an external magnetic field is applied, called magnetorheological (MR) effect. When a conductive filler is added to a magnetorheological elastomer, the resulting hybrid filler composite showcases both MR and piezoresistive effects. For such a reason, these composites are referred to as self‐sensing magnetorheological elastomers. In this case, the synthesized self‐sensing magnetorheological elastomers are based on styrene‐based thermoplastic elastomers (TPS), carbonyl iron particles (CIP), and carbon black (CB). The hybrid filler concept using various coated CIP and constant CB content showed that above 25 vol.% CIP the resistivity increased rapidly. This work proposes the first case of a 3D printable self‐sensing magnetorheological elastomer and cyclic mechanical compression and tensile mode analysis at high deformation (up to 20% and 10%, respectively). The results showcase a magnetoresistive change of up to 68% and a piezoresistive change of up to 42% and 98% in compression and tension, respectively. In addition, the magnetostriction of the self‐sensing samples has been characterized to be 3.6% and 5.6% in the case of CIP 15 and 30 vol.%, respectively.

3D finite element simulation of scratch testing to quantify experimental failure mechanisms of a thin film

In this work, an exhaustive finite element (FE) simulation was developed to closely reproduce experimental parameters such as normal force, tangential force, and penetration depth along the whole scratch test. We used an 800 nm thick Ti–Al–N thin film deposited by sputtering as the reference sample to carry out scratch tests identifying the appearance of failure mechanisms at different longitudinal displacements and critical loads. The hardening models of thin film and substrate allowed us to quantify the maximum principal stresses responsible for thin film spallation, about 14.5 GPa for the tensile mode and −1.49 GPa for the compression mode. These parameters provided an improved perspective to characterize the failure mechanisms on the sample during the scratching. The present enhanced 3D FE simulation can be a crucial tool for designing film-substrate systems with more precise mechanical strength calculations.

Aerosol Jet Printing of Strain Sensors for Soft Robotics

The field of soft robotics is rapidly progressing toward applications including; wearable electronics, prosthetics, and biomedical devices. This is leading to demand for flexible, embedded high‐performance strain sensors to deliver real‐time feedback on the static configurations and dynamic motions of these robotic devices, to ultimately enable the levels of autonomous control and structural monitoring required for intelligent manipulation. Herein, aerosol jet printing (AJP) technology is utilized to generate arbitrary piezoresistive strain sensor layouts on fibrous paper suitable for direct integration into elastomeric soft robots. A custom graphene nanoplatelet ink with a viscosity of around 2.70 cP has been formulated for optimized atomization and patterning of conductive traces via AJP. Single and multilayer printing onto different paper substrates are explored; with the nominal resistance of the printed tracks varying from 272 to 4900 kΩ depending on paper type and number of layers. Maximum gauge factors of 24.2 ± 1.8 and 56.5 ± 4.5 are determined for sensor surfaces under tensile and compression modes, respectively. To demonstrate the possibility for direct integration of this approach for soft robotics, strain sensors are directly printed onto the strain‐limiting layer of a pneumatic soft robotic gripper, to provide continuous feedback of the gripper over curvatures up to 80 m−1.

Study on influence of parameters of buckling behavior in soft mechanical metamaterials

Mechanical metamaterials are valued for their diverse properties and potential applications. Due to the instability and large deformability of soft mechanical metamaterials (SMMs), geometric reorganization will occur and lead to some unusual properties. It is possible to change the properties of materials by varying the parameters. Conventional SMMs contain a periodic distribution of holes with the same size and shape, which can be changed to a lesser extent. Periodic dispersion of regular through-hole patterns of various sizes or shapes into elastomers, resulting in metamaterials with more mechanical functionality and deformation scenarios. In this paper, we investigated the influence of parameters on the buckling mechanical behavior of SMMs and the buckling mechanical behavior of structures with multiple sizes and geometric shapes. The parameters studied include geometric parameters (pore shape, porosity and area ratio) and physical parameters (Poisson’s ratio and compression mode). Simulation of the buckling behavior of SMMs uses the finite element method. The finite element software ABAQUS is used, taking into account the almost incompressible characteristics of materials, the triangular quadratic plane strain hybrid element is selected (CPE6H). Numerical calculation gives the following results: Area ratio, pore shape and compression mode have obvious effects on buckling behavior, but Poisson’s ratio has little effect; the influence of parameters on the buckling critical strains varied for SMMs with various pore shapes; very different buckling behaviors will result from swapping out the pattern of holes with the same size or shape for holes with two different sizes or shapes; the expression of buckling behavior is also varied when the mix of hole shapes is modified. These findings demonstrate that the design parameters may be used to achieve the desired buckling behaviors. This is a new method that can be used to control the deformation of structures; modify the properties of the SMMs without changing stiffness; simplify the structures without significantly changing the material properties. The design path of mechanical metamaterials is increased.

Compression of filled, open-cell, 3D-printed Kelvin lattices

The sensitivity of compressive strength of a polymeric Kelvin lattice to the presence of an epoxy core has been investigated both experimentally and numerically. Crush bands develop in the empty lattice, with large oscillations in load due to geometric softening and the sequential fracture of successive layers of struts. In contrast, the epoxy core has a sufficiently high modulus and strength that outward lateral flow of the epoxy through the open-cell lattice is negligible: the boundary layer, wherein migration of epoxy occurs through the lattice, extends less than one cell size from the surface of the specimen. The epoxy core supports the struts and stabilises the bulk macroscopic response against crush band formation. Finite element analysis of periodic unit cells show that the presence of an almost incompressible epoxy core changes the deformation mode of the lattice from one that is close to uniaxial straining to an isochoric mode. However, both the compressible collapse mode of the empty lattice and the isochoric deformation mode of the filled lattice are bending-dominated. At finite strain, the observed macroscopic strength of the filled lattice is degraded by bending failure of the struts and by tensile cracking of the adjacent core; the failure location is at a particular subset of the nodes of the lattice. Microcrack coalescence leads to the formation of a series of vertical fissures in the specimen.

Strengthening the Key Features of Volumizing Fillers: Projection Capacity and Long-Term Persistence.

Volumizing fillers aim to create or restore facial volume in fat layers. To provide strong tissue lifting and long-term persistence, gels are generally designed with stiff properties, characterized by a high storage modulus (G'). However, clinical evidence shows a discrepancy between high G' and good lifting capacities, especially after skin tension has been exerted on the gel. To better explore the in vivo behavior of a gel, we first evaluated the elastic moduli of five commercial volumizers (RHA4, JUVVOL, RESVOL, RESLYFT, and BELVOL) in dynamic compression mode, E'. We further developed a Projection Index score based on the rheological assessment of creep in compression to mimic skin tension-induced stress relaxation (flattening). Finally, the ability of a gel to resist enzymatic degradation was analyzed with a multidose approach. Despite similar clinical indications, volumizers exhibited distinct behaviors. RHA4 and BELVOL showed the highest E' values (resistance to strain), RHA4, JUVVOL, and RESVOL exhibited the greatest projection capacities, while JUVVOL and RHA4 offered the largest persistence to enzymatic degradation. In this article, we introduce the use of the Projection Index to efficiently assess the ability of a gel to lift tissues, thus increasing preclinical models' efficiency and reducing the need for animal studies.

Nano/micro-beam deflections: Investigation of subjected forces and applications

Micro- and Nano beam MEMS devices possess a broad range of applications owing to their capability to produce precise mechanical motion and sensing capabilities at a small scale. In the field of biomedicine, these devices have been employed in applications such as tissue engineering, lab-on-a-chip systems, and implantable devices. Medical devices, particularly those involved in drug delivery, are significantly impacted by the forces applied to them. Therefore, it is imperative to carefully evaluate the effects of axial force and optimize the device's design to ensure that it can endure the forces it will encounter during operation. Despite being relatively weak, the van der Waals force warrants careful consideration when working at the micro- and nanoscales. In this research, the nonlinear equation obtained by the Galerkin method for a doubly clamped nano/micro-beam under the effect of Van der Waals (vdW) force was solved. The Homotopy Perturbation Method (HPM) and the Akbari Ganji Method (AGM) are introduced to investigate the nonlinear problem in this paper analytically. To validate and investigate the accuracy of the AG and HP methods, the obtained results were compared to the Runge-Kutta approach. The obtained results for all data sets showed the high accuracy of the AG and HP methods. Also, this paper investigated the effect of axial force N on beam type N/MEMS deflection. The axial force N effect in both tensional (N > 0) and compressive (N < 0) modes has been investigated. Due to the obtained results, increasing the axial force compressively increases the deflection of the beam. However, this trend is reversed for the tensional axial force.