Cyclic Compression Tests Research Articles

Mechanical Properties and Vibrational Behavior of 3D-Printed Carbon Fiber-Reinforced Polyphenylene Sulfide and Polyamide-6 Composites with Different Infill Types

The aim of the present study is to investigate the performance of two carbon fiber-reinforced composite polymers used to manufacture end-use parts via the fused filament fabrication (FFF) method. The materials under investigation were carbon fiber-reinforced Polyamide-6 (PA6-CF15) and carbon fiber-reinforced polyphenylene sulfide (PPS-CF15). To evaluate their mechanical properties and vibrational behavior, specimens were fabricated with four distinct infill patterns: grid, gyroid, triangle and hexagon. In particular, the vibrational behavior of the 3D-printed composites was determined by conducting cyclic compression testing, as well as modal tests. Additionally, the mechanical behavior of the reinforced polymers was determined by conducting both uniaxial tensile and compression tests, as well as three-point bending tests. The results of the mechanical experiments revealed that the grid pattern exhibited the best overall performance, while the gyroid pattern exhibited the greatest strength-to-weight ratio, making it the most durable infill for use with composite filaments. In vibration experiments, PA6-CF15 structures exhibited higher damping ratios than PPS-CF15, indicating superior damping capacity. Among the infill patterns, the hexagon pattern provided the greatest vibration isolation performance.

Programable shape recovery properties and snap-through instabilities of viscoelastic and shape-memory NS metamaterials

The combination of smart material and mechanical metamaterial has the potential to bring novel properties and additional functionalities, which, however, has been ignored for a long time. This work numerically, experimentally, and analytically examines the negative stiffness (NS) metamaterials based on shape memory polymers (SMPs) with a focus on the tunable and temperature-dependent properties induced by the interaction of material and geometry nonlinearity. A universal discrete model of a series of shape-memory NS metamaterial is developed by separating the bending effect and stretching effect, where the viscoelastic material is described by the generalized Maxwell-Wiechert model, and an SMP constitutive model is proposed based on multiplicative decomposition of the deformation gradient. The mechanical and shape-memory properties influenced by temperature, geometry, material and loading rate are experimentally observed through relaxation tests and cyclic compression tests. Then the discrete model and finite element analysis (FEA) is adopted to examine the novel mechanical responses in a wide range of parameters. Results show that viscoelasticity and loading rate play a significant role in mechanical responses, and tunable load-capacity and stability can be achieved for shape-memory metamaterial. A phase diagram of different stabilities is constructed showing strictly monotonic, S-shaped, and snapping responses. Additionally, repeated compression and recovery performance proves the possibility of reusable applications. This work provides new opportunities for functional metamaterial to obtain programmable shape recovery and mechanical responses.

Stretchable and self-healing carboxymethyl cellulose/polyacrylic acid conductive hydrogels for monitoring human motions and electrophysiological signals.

Stretchable conductive hydrogels have attracted great attention in flexible electronics. Nevertheless, conductive hydrogels would suffer from an inevitable damage during use, significantly reducing the reliability and limiting the practicability. Herein, stretchable and self-healing conductive hydrogels are designed form carboxymethyl cellulose (CMC), polyacrylic acid (PAA), and Fe3+, which are applied for monitoring human motions and electrophysiological signals. The plentiful H-bonding and metal coordination endow the conductive hydrogels with good mechanical (fracture strain: 917 %; fracture stress: 202 kPa; toughness: 1.1 MJ m-3) and self-healing properties. After self-healing, the fracture stress is almost fully recovered, the fracture strain is restored to 72 %, and the conductivity is reestablished to 98 %. The conductive hydrogels show good fatigue resistance during cyclic tensile and compressive loading-unloading tests. Furthermore, the mechanical deformation would lead to the resistance change of the hydrogel to realize the electrical signal record. So, the hydrogel was assembled into a flexible wearable sensor that has good electrical conductivity (0.779 S m-1), fast responsiveness (response time: 300 ms; recovery time: 200 ms) and high sensitivity (gauge factor (GF) = 7.99, 400-650 %). This work demonstrates a simple and efficient strategy for developing stretchable and self-healing conductive hydrogels in healthcare monitoring and flexible electronics.

On the Design of a Combined Cyclic Axial Compression and Bending Test Program for a Subsea Power Cable

On the Design of a Combined Cyclic Axial Compression and Bending Test Program for a Subsea Power Cable

Frontal polymerization of acrylamide/GelMA/gelatin hydrogels with controlled mechanical properties and inherent self-recovery

Low mechanical resistance represents one of the significant problems of hydrogels, limiting their applicability in many fields. One approach to overcome this issue is synthesizing interpenetrating polymeric networks. In this work, the frontal polymerization technique was used to synthesize two series of novel hydrogels: (i) poly(acrylamide) (PAAm)-based hydrogels copolymerized/crosslinked with methacrylate gelatin (GelMA) (AAm-GelMA copolymer networks), and (ii) semi-IPN made of AAm-GelMA copolymer networks and a physically crosslinked gelatin network. With the final objective of improving the rheological, mechanical, morphological, thermal, and swelling properties of PAAm hydrogels, GelMA with two different degrees of methacrylation (30 and 75 mol%) was used. Interactions between GelMA chains, which give rise to physical network formation (i.e., GelMA-GelMA interactions), resulted in very efficient crosslinking for PAAm-based hydrogels, requiring a significantly lower methacrylic group concentration (0.04 mol%) for hydrogel formation compared to N,N′-methylene-bis-acrylamide (1 mol%), which is the agent typically used as a crosslinker for PAAm. Furthermore, the degree of GelMA methacrylation markedly affected the properties of the hydrogels. For example, regarding the swelling degree, hydrogels containing 22 wt% of GELMA30 had an SR% of 2870, while those containing the same amount of GELMA75 swelled much less (870 %). The introduction of gelatin as a secondary network in semi-IPNs influenced the rheological and mechanical properties, resulting in increased hydrogel modulus and stiffness attributed to enhanced physical interactions within the network. Finally, dynamic rheological shear strain and cyclic loading compression tests demonstrated exceptional recovery capabilities in all hydrogel formulations: samples subjected to alternating low (0.1 %) and high (300 % or 10 %) shear strain demonstrated a complete and prompt recovery of G′ and G″ values.

Mechanical characterization and structural analysis of elastodontic appliances under intraoral and artificial aging conditions

BackgroundThis study focused on the aging mechanism and degradation of mechanical and structural features of elastodontic appliances (EA) under artificial and intraoral aging to achieve oral myofunctional therapy with particular removable silicone elastomer devices.Materials and methodsEAs artificially aged in saliva with different pH values were investigated through cyclic compression testing along with characterization techniques (Scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy), and characterization analysis was also performed on clinically retrieved EAs.ResultsArtificial aging was found to have minimal effect on the structural properties of EAs, and intraorally aged samples showed perceptible micro-morphology. The Mullins index and peak stress decreased (P<0.01), while the compression set increased with prolonged aging time. Samples in alkaline saliva showed the largest Mullins effect (P<0.05).ConclusionsThe aging mechanism of the elastomer was found to be the crosslinking of main chains and scission of side chains. The presence of OH- enhanced the rupture degree of side bonds. The decline in viscoelastic properties was shown to be more severe with longer service durations.Clinical relevanceResearch on how the salivary environment and pH affect the aging characteristics of EAs is vital for guiding clinical applications and future modifications to extend their clinical lifetime.

Mechanical Behaviors of Orthogonal Spiral Metal Skeleton–Polyurethane Elastomer Composites under Complex Loading Modes

Herein, a novel material design strategy is proposed: an interpenetrating composite composed of a woven orthogonal spiral metal skeleton and polyurethane (PU) elastomer. This interpenetrating composite combines rigidity and flexibility, exhibiting excellent elasticity and deformation recovery. The deformation behavior and mechanical properties of the composites under various loading conditions are investigated through experiments and numerical simulations. Different degrees of warping behaviors occur in composites with various structural parameters under uniaxial tension. Alternating rotations and double spiral arrangements can significantly limit the warping phenomenon, with a maximum reduction of 78%. The bending load capacity is regularly increased by increasing the wire diameter and decreasing the pitch. Increasing the number of loaded spiral wires enhances the bending load capacity of the composites. Uniaxial compression tests demonstrate that the composites have excellent load‐carrying capacity and strain recovery, with compressive strength 1.5 times that of pure PU. Cyclic compression tests further illustrate the excellent energy consumption capacity and stability of the composites. Overall, the introduction of orthogonal spiral skeletons into the composites demonstrates the potential to achieve enhanced load‐carrying capacity and large strain recovery simultaneously.

Study on the evolution rules of coal deformation and failure characteristics caused by multiple mining disturbances

During coal mining operations, the coal will be deformed and damaged due to multiple mining disturbances (MMD), often resulting in disasters, like rock burst. To understand the evolution rules of coal deformation under MMD and its final fracture characteristics after impact dynamic load loading, reduce the adverse effects of mining disturbances, and improve disaster prevention and control capabilities, quasi-static uniaxial cyclic loading-unloading (L-U) and dynamic axial compression tests were conducted on large-sized coal-like samples. During the tests, three-dimensional (3D) laser scanning and acoustic emission (AE) monitoring technology were utilized to accurately capture the full-field deformation and AE response data, facilitating a systematic analysis of deformation and fracture characteristics. The results show that: (1) Under the cyclic L-U effect induced by MMD, each loading cycle causes compression deformation with partial recovery during unloading, presenting an overall “wavy” variation trend. (2) The maximum load is the most critical factor affecting the damaged coal deformation, with smaller load resulting in less overall sample deformation. (3) After the impact dynamic loading, the damaged samples suffered large-scale impact splitting failure, with the compressive-shear layer failure mainly occurred inside the holes. (4) Lower loading during cyclic L-U process correlate with reduced damage degree, and smaller debris particles with a higher fractal dimension when impact failure occurs, indicating a more severe impact failure. (5) With multiple cycles of L-U, the cracks inside the sample gradually extend and expand from around the hole to the outside. The greater the load and the number of cycles, the more serious the crack damage will be. (6) In the practical mining process, it is crucial to reinforce roadway interiors while minimizing low-loading cyclic disturbances induced by MMD. The study has obtained the deformation evolution rules and failure characteristics of coal under MMD, providing a theoretical basis for the prevention and control of corresponding engineering disasters.

Experimental and model evaluation of cyclic compressive performance for RAC-filled BFRP tube composite columns

The mechanical properties of recycled aggregate concrete (RAC) can be significantly enhanced in RAC-filled fiber-reinforced-polymer (FRP) tube composite columns. However, the cyclic compressive behavior of this type of composite columns has been scarcely studied. In this study, a series of cyclic axial compressive tests were conducted on RAC-filled basalt-FRP (BFRP) tube composite columns, and the effects of confinement level (number of BFRP layers) and RA replacement ratio were investigated. The test results indicate that, compared to RAC columns, the compressive capacity and deformability of RAC-filled BFRP tube composite columns increased significantly under cyclic loading. The compressive strength and ultimate strain of BFRP-confined RAC reached 1.42–3.98 times and 2.88–21.53 times those of unconfined RAC, respectively. The compressive strength and ultimate strain under cyclic loading were generally close to those under monotonic loading, with the compressive strength ratios averaging 1.052 and the ultimate strain ratios averaging 1.031. The enhancement efficiency of BFRP confinement increased progressively with increasing confinement level and/or RA replacement ratio. The envelope curves of the cyclic stress-strain curves resembled the stress-strain curves under monotonic loading. The reloading modulus (Ere) and residual modulus (Eun,0) continuously decreased as the unloading strain (εun) increased, while the plastic strain (εpl) increased almost linearly with εun. The values of Ere, Eun,0 and εpl were affected by the confinement level and RA replacement ratio. Finally, typical theoretical models for FRP-confined concrete were used to evaluate the cyclic stress-strain curves of RAC-filled BFRP tube composite columns.

Factors influencing static and cyclic behaviour of polymer-grouted sands

ABSTRACT In this study, thorough laboratory research was conducted in order to increase knowledge of the beneficial effect of water-soluble epoxy resin on the monotonic or cyclic triaxial strength of different sands. Seven sand fractions (with different particle sizes, uniformity coefficients and mineralogical compositions) were injected with solutions of epoxy resin and water, at ratios of 3.0, 2.0 and 1.5. To evaluate the influence of chemical treatment on the static strength behaviour of grouted sands, a series of monotonic triaxial tests on dry specimens and isotropically consolidated undrained (CIU) triaxial tests, were conducted on samples cured for 90 days. CIU cyclic triaxial compression tests were also performed, to assess improvements in the cyclic resistance of treated sands. The experiments showed that this resinous grouting resulted in an appreciable increase in cohesion values, particularly for fine sands and well-graded sands, ranging from 0.15 to 0.66 MPa. Despite the fact that friction angle values were reduced, the overall shear strength increased over a wide range of stresses. Moreover, all grouted sands exhibited a substantial improvement in cyclic properties, with failure occurring at significantly elevated stress levels and after enduring a larger number of loading cycles, compared to their untreated counterparts.

An environmentally friendly and superhydrophobic melamine sponge self-roughened by in-situ controllably grown polydopamine nanoparticle for efficient oil-water separation

The preparation of conventional superhydrophobic sponges inevitably requires the involvement of noxious and non-degradable raw materials，thus threatening ecosystems. As reported herein, an environmentally friendly and superhydrophobic melamine sponge is facilely prepared for efficient oil-water separation, which is completely derived from eco-friendly substances. The formation of a hierarchical structure on the sponge skeleton was achieved via the in-situ controllable growth of polydopamine nanoparticles in mildly alkaline solution. In addition, octadecyl amines (ODA) with long chains of hydrophobic alkyl groups were grafted onto the polydopamine coating to reduce the surface energy through Schiff base or Michael addition reactions. Ultimately, the resulted sponge possessed extreme water repellency with a water contact angle (WCA) of 153.21 ± 1.31° and could retain its superhydrophobicity when it was exposed to solutions with different pH values and high temperature. Moreover, the resultant sponge exhibited fully reversible compressibility with up to 80 % strain and excellent structural stability after 200 cyclic compression tests. Meanwhile, distinct organic liquid absorption experiments were conducted to confirm the resulted sponge with excellent oil absorption capacity (73.46–119.66 g/g) and oil-water separation properties. Therefore, the as-prepared superhydrophobic sponge provides valuable insight into efficient oil-water separation.

Validation of a three-dimensional finite element constitutive modeling approach for a thermoplastic polyurethane calibrated with uniaxial tests

This paper presents the three-dimensional finite element constitutive modeling validation for a Thermoplastic Poly-Urethane (TPU) material. The material parameters are those given in a previous study obtained by calibrating the constitutive model with uniaxial material-level test results (1-D tensile and compression tests). Confined compression tests were performed to estimate the bulk modulus for more accurate material characterization. The parameters were validated by comparing the results of experimental tests on TPU components with those obtained by its equivalent finite element simulations. The TPU component tests comprised cyclic compression tests of (i) a TPU cylinder, (ii) a solid 100 mm diameter TPU ball, and (iii) a 100 mm diameter TPU ball with an 80 mm steel core. In all tests, the constitutive model parameters showed an excellent performance in representing the mechanical behavior of the material observed in the tests, including the nonlinear stiffness and hysteresis. Finally, a brief case study is presented to illustrate the applicability of the validated constitutive model parameters in modeling a novel TPU damper for structural control before its manufacturing and experimental testing. The validated constitutive modeling approach and available material parameters will allow the performance of reliable and early-stage finite element simulations to prototype the mechanical behavior of TPU components of different shapes and boundary conditions and thus gain relevant insight into the component level response before manufacturing and testing.

Flexible AgNW/PDMS nanocomposite for strain and pressure sensing

This study presents the fabrication and characterization of an ultra-thin (<1 mm) piezoresistive sensor based on a silver nanowire (AgNW) and polydimethylsiloxane (PDMS) nanocomposite, capable of simultaneous strain and pressure sensing. The sensor exhibits high sensitivity, detecting strains as low as 0.5 % with a range of up to 40 %, demonstrates frequency responsiveness from 0.5 to 3 Hz, and maintains functionality over 1000 cycles. The sensor’s performance was evaluated through cyclic tensile and compressive tests. We hypothesize that the compression sensing mechanism is a consequence of the Poisson effect in the PDMS substrate, where transverse compression induces axial strains parallel to the AgNW network, causing disconnections within the nanowire matrix. The sensor’s versatility was demonstrated through various biofeedback applications, including finger bending, applied pressure, calf raises, and elbow flexion. With its thin profile and dual-mode sensing capability, this AgNW/PDMS nanocomposite sensor shows promise for biomechanics, sports science, and healthcare monitoring applications.

Crack Evolvement of Ancient Brick Masonry Under Uniaxial Compression Fatigue Loading

ABSTRACT Cracking is an essential intuitive indicator of damage in masonry structures. Evaluating the progression of fatigue cracks in ancient brick masonry structures is vital for the preservation and safety of ancient buildings. By conducting amplitude cyclic uniaxial compression tests on ancient brick masonry specimens, using the video image correlate-3d (VIC-3D) technology to collect images of the entire process from loading to failure, the development of fatigue cracks is analyzed and concluded. A reversed S-shaped function for fatigue crack evolution was established based on the fatigue damage mechanism. The model parameters’ physical significance, value range, and their impact on the model curve were discussed. The fatigue damage evolution equation was derived from the fatigue crack evolution model. The research results show that a reversed S-shaped function for fatigue crack evolution covers various types of fatigue crack evolution laws, with strong adaptability and high accuracy. The damage evolution curve established, based on the fatigue crack evolution model, has a reversed S-shaped change rule, and was divided into three stages: the first stage (0 N f ~ 0.1 N f ) fatigue damage grows faster; the second stage (0.1 N f ~ 0.9 N f ) fatigue damage growth is stable, close to linear change; when the cycle ratio exceeds 0.9, it enters the third stage, and fatigue damage increases rapidly.

Superior damage tolerance observed in interpenetrating phase composites composed of aperiodic lattice structures

Interpenetrating Phase Composite (IPC) metamaterials, based on lattice topologies, have garnered significant attention as advanced materials for structural applications. However, conventional IPCs, which rely on periodic lattice unit cells, are prone to catastrophic failure due to their global deformation modes. To overcome this limitation, we present a novel IPC design utilizing aperiodic truss unit cells, inspired by the elusive “Einstein” monotile pattern. Our concept is demonstrated through IPC 3D printed via polymer jetting, using a hard polymer as the lattice filler and a soft polymer as the matrix. The distinctive mechanical properties of IPCs are characterized through single and cyclic quasi-static compression testing. Our findings demonstrate that aperiodic IPCs enable progressive deformation with gradual compression stress plateaus. Additionally, aperiodic IPCs exhibit remarkable damage tolerance, retaining 67.59 % of residual energy absorption and 73.83 % of ultimate strength after multiple cyclic compressions up to 30 % strain. These mechanisms are attributed to the synergistic deformation of interconnected unit cells, which lead to self-adjusting plastic collapse, progressive displacement evolution and delocalized deformation. This aperiodic concept paves the way for developing high-performance cushioning protection materials.

Fatigue resistant photo-responsive [c2] daisy chain Poly(rotaxane) hydrogel

A photo-responsive poly(rotaxane) hydrogel based on [c2] daisy chain was synthesized. The supramolecular hydrogel was robust with the compression stress of 3136 kPa at the strain of 90 %, the tensile strength of 297 kPa and the elongation at break of 694 %. At the same time, the gel film showed fast photoresponsive behavior even in dry state, showing 15o bending angle under 2 s 365 nm UV irradiation. Besides, the hydrogel exhibited good fatigue resistance. Its recovery ratio remains higher than 80 % during multiple cyclic tensile and compression test, making it an alternative and promising platform for photo-responsive materials with emergent mechanical performances and attractive fatigue resistance.

Alternatives for Enhancing Mechanical Properties of Recycled Rubber Seismic Isolators.

Base isolators, traditionally made from natural rubber reinforced with steel sheets (SERIs), mitigate energy during seismic events, but their use in developing countries has been limited due to high cost and weight. To make them more accessible, lighter, cost-effective reinforcement fibers have been utilized. Additionally, the increasing use of natural rubber has caused waste storage and disposal issues, contributing to environmental pollution and disease spread. Exploring recycled rubber matrices as alternatives, this study improves seismic isolators' mechanical properties through modified reinforcements and layer adhesion. Eight reinforcement materials and eight adhesives, which may be activated with or without heat application, are systematically evaluated. Employing the chosen reinforcements and adhesives, prototypes are tested mechanically to examine their vertical and horizontal performance through cyclic compression and cyclic shear testing. Two innovative devices using recycled rubber matrices were developed, one using a layering technique and another through a monolithic approach shaped with heat and pressure. Both integrate a fiberglass mesh reinforced with epoxy resin; one employs a heat-activated hybrid adhesive, while the other uses a cold bonding adhesive. These prototypes exhibit potential in advancing seismic isolation technology for low-rise buildings in developing countries, highlighting the viability of recycled materials in critical structural applications.

Effect of cyclic loading level on mechanical response and microcracking behavior of saturated sandstones: Correlation with water weakening phenomenon

Rocks frequently endure water environments and diverse cyclic loading from natural and anthropogenic sources across various damage stages. Understanding the mechanical and fatigue behavior of saturated rocks under different cyclic loading levels is crucial for the intelligent design and long-term stability of the slope. Here, we report several monotonic and cyclic compression tests conducted on red and cyan sandstones under dry and water-saturated conditions, coupled with acoustic emission (AE) monitoring. We analyzed key mechanical parameters such as peak stress and peak strain, as well as AE parameters including count and energy, and dominant frequency in AE spectra. Our findings reveal that elevated cyclic loading levels significantly reduce peak stress and increase peak strain in both dry and water-saturated rocks, with more pronounced effects observed under water-saturated condition. The cumulative AE count correlates positively with increasing cyclic loading levels but decreases due to water saturation. Under cyclic loading with varying levels, dry rocks often experience shear cracking and exhibit AE waveform with high dominant frequency, while saturated rocks tend toward tensile cracking and AE waveform with low dominant frequency. Higher cyclic loading intensifies the occurrence of tensile cracking and AE waveform with low dominant frequency, which are constrained during the elastic deformation stage but become more pronounced beyond the crack initiation threshold. Moreover, cyclic loading enhances the water weakening effects in saturated rocks, closely associated with ongoing crack propagation within the rocks.

Effects of Direct Aging Heat Treatments on the Superelasticity of Nitinol Produced via Laser Powder Bed Fusion

This work investigates the effects of short-time direct aging heat treatments on the mechanical properties and microstructure of additively manufactured Nitinol (NiTi) alloy. Cylindrical samples were produced through laser powder bed fusion (L-PBF), directly aged at different temperatures and compared to the solution annealed and aged conditions. Compression tests were carried out at room temperature both in cyclic mode at constant strain and incremental cyclic mode, to provide a comprehensive analysis on the superelastic features of NiTi after direct aging heat treatments. Furthermore, cyclic compression tests were performed at 37 °C to evaluate the superelastic effect at the body temperature and, therefore, the possibility to use these treatments for biomedical components. The effects of direct aging on the microstructure were characterized using transmission electron microscopy (TEM). High cyclic stability and superelastic recovery up to 10 pct of deformation emerged for the direct aged alloys. The comparable results obtained with and without the solution treatment points out that this step was not necessary in reaching superelasticity, proving the effectiveness of direct aging.

Comparative study on seismic behavior of corroded RC columns strengthened by ECC combined with steel cage /fiber grid/CFRP

A method for strengthening was proposed to improve the seismic behavior of corroded reinforced concrete (RC) columns by using engineered cementitious composite (ECC) combined with a steel cage/fiber grid/carbon fibre reinforced plastics(CFRP). The corroded RC columns strengthened with ECC combined with a steel cage, fiber grid, and CFRP were subjected to low cyclic compression tests at design axial pressure ratios (n) of 0.3 and compared with corroded and uncorroded columns. Experimental results showed that ECC strengthening of corroded RC columns not only significantly improved their load-carrying capacity, displacement ductility, and energy dissipation capacity but also effectively reduced the degree of damage and stiffness degradation. The ductility coefficients of ECC/steel cage composite strengthened columns and ECC/CFRP composite strengthened columns are 35.58 % and 34.13 % higher, respectively, compared to ECC fully strengthened columns, while the ductility coefficient of ECC/fiber grid composite strengthened columns decreased by 4.33 % compared to ECC fully strengthened columns. Among them, the ECC/steel cage composite-strengthened columns exhibited the highest number of hysteresis loops, the strongest energy dissipation capacity, and the best strengthening effect. Additionally, a restoring force model for ECC-strengthened corroded RC columns was established, and its validity was verified through theoretical calculations.