Cyclic Compressive Loading Research Articles

Constitutive model for ultra-high performance concrete (UHPC) considering the size effect under cyclic compressive loading

In this study, the size effect of the thickness of the specimen on the mechanical properties of UHPC was investigated through compression tests under cyclic loading. UHPC prisms with different thicknesses from 20 mm to 100 mm were tested under unloading/reloading cycles and the stress–strain curves were recorded for this purpose. A constitutive model to predict the stress–strain response of UHPC accounting for the thickness was proposed. It was found that UHPC specimens with different thicknesses showed the same failure mode of diagonal shear failure. The size effect of thickness was significant for the compressive strength but was negligible for the peak strain and elastic modulus. The damage of the unloading modulus and reloading modulus at zero stress only occurred when the unloading strain exceeded 0.8 times the peak strain. Furthermore, the proposed constitutive model could predict the stress–strain response for UHPC with different thicknesses under cyclic compressive loading with acceptable accuracy.

Enhancement in the fatigue resistances of triply periodic surfaces-based scaffolds

To improve the endurance limits of triply periodic minimal surface (TPMS)-based scaffolds, the post-treatment process combing hot isostatic pressing (HIP) and electropolishing (ELP) was proposed and conducted in TPMS-based scaffolds with various structures. Thus, the fatigue properties were enhanced from three aspects: changing the topological structures of TPMSs, improving surface qualities and eliminating internal defects. The stretching-dominated scaffold-new diamond (AD) and the bending-dominated scaffold-network-based gyroid (IG) were selected and their relative densities were set to 20%. These scaffolds were fabricated by electron beam melting using Ti6Al4V powders. HIP and ELP were conducted in the manufactured scaffolds. Then, compression–compression fatigue tests were performed and fatigue parameters such as fatigue life, accumulated strain rate, fatigue strength and fatigue ratio were obtained. The experimental techniques of scanning electron microscopy, microcomputer tomography, optical microscopic, X-ray diffraction and electron backscattered diffraction were carried out to characterise the surface qualities, internal defects and microstructures. The effects of topological structure and surface quality on the stress distribution on TPMS-based scaffolds under compressive loading were investigated by finite element analysis. Results show that topological structures, surface qualities and internal defects all affect the fatigue properties of TPMS-based scaffolds. Under cyclic compressive loading, the fatigue ratios of IG and AD without undergoing post-treatment are 0.11 and 0.59, respectively, while they rise to 0.26 and 0.69 after HIP and ELP. Compared with surface qualities and internal defects, topological structures influence the fatigue properties of TPMS-based scaffolds more prominently. The fatigue properties of TPMS-based scaffolds can be enhanced by the post-treatment process combing HIP and ELP, and greater improvement will be obtained for bending-dominated structures than stretching-dominated structures. Thus, manipulating the topological structures and increasing the buckling components of TPMS-based scaffolds is an effective way to obtain porous scaffolds with excellent fatigue properties under cyclic compressive loading. HIP and ELP can also be adopted to further improve their fatigue lives. The novelty of this study lies in improving the fatigue properties of TPMS-based scaffolds from the three aspects, which are changing the topology structure, improving the surface quality and reducing the internal defects, and the mechanisms of improving the fatigue properties of TPMS-based scaffolds are systematically discussed.

Improving conductivity and self-sensing properties of magnetically aligned electroless nickel coated glass fiber cement

The nickel coated glass fiber (Ni-GF) cement (NGFC) holds promise for self-sensing concrete structure due to its improved conductivity and corrosion resistance. This paper is aimed at evaluating the conductivity and self-sensing properties of preferentially orientated NGFC, which was prepared by the magnetic field (MF) induction. The microstructure of electroless Ni-GFs and their arrangement characteristic in cement were observed by optical microscope (OM), scanning electron microscope (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD). The anisotropic conductivity and self-sensing properties of as-prepared composites were measured by four-electrode method. The results indicate that the Ni-GFs with uniform nickel coating layer in the as-fabricated composite have an excellent alignment effect under the MF induction. When the Ni-GF content is 2.62 vol%, the composite exhibits maximum anisotropy. The order of the electrical resistivity and percolation thresholds of NGFC is: parallel to MF < without MF < perpendicular to MF. Under the cyclic compression load, the NGFC parallel to MF shows the optimum self-sensing properties. With the increase of loading amplitude and decrease of loading rate, the maximum sensitivities of the as-prepared composite at all directions almost increase linearly. Under the failure compression load, the conductivity of as-prepared composites parallel to MF show a steadier and higher self-sensing response.

3D printed flexible wearable sensors based on triply periodic minimal surface structures for biomonitoring applications

Soft piezoresistive wearable conductors have led to a paradigm shift in the monitoring of human bodily motions. Cellular additively manufactured conductors are promising piezoresistive components as they offer mechanical tunability and provide controllable percolation pathways. In the present study, we engineer high surface-area cellular structures with the triply periodic minimal surface (TPMS)-based architectures to tailor their piezoresistive response for use in wearable devices. A simple and economical fabrication process is proposed, wherein a fused deposition modeling 3D printing technique is utilized to fabricate flexible thermoplastic polyurethane (TPU) cellular structures. Interconnectivity of TPMS designs enables the coating of a continuous graphene layer over the TPU internal surfaces via a facile dip-coating process. The effects of pore shape on piezoresistivity are studied in four different TPMS structures (i.e. Primitive, Diamond, Gyroid, and I-WP). Mechanical properties of sensors are evaluated through experimental procedures and computation methods using finite element analysis of the Mooney–Rivlin hyperelastic model. The piezoresistive performance of sensors exhibits durability under cyclic compression loading. Finally, we conclude that the Primitive structure offers suitable piezoresistive characteristics for sensing of walking, whereas the Diamond structure presents favorable results for respiration monitoring.

Lubricant performance against white etching areas (WEAs) formation in AISI 52100 bearing steel under cyclic compressive loading

Premature bearing failures commonly occur in applications that operate under extreme boundary conditions. The lubrication engineers and tribologists are confronting a key challenge in these bearing failures associated with microstructure decay, such as White Etching Cracks (WECs) and White Etching Areas (WEAs). Lubricant degradation is one of the critical factors for the subsurface decay in the bearing steel. This work evaluates the performance of mineral oil (heavy paraffin oil) and synthetic poly alkyl glycol (PAG) against WEAs formation under pure sliding with cyclic compressive loading. The performance of lubricants was evaluated using Infrared Fourier Transform (FTIR) and Electron Spin Resonance (ESR) spectroscopy. The outcomes reveal that the free radical formation rate is higher for paraffin than PAG. This study found that WEAs formation in the bearing steel is delayed in the PAG tested samples compared to paraffin.

Seismic performance of concrete-filled steel tube columns using ultra-high-strength steel under long-period ground motion demands

The long-period ground motions observed in recent subduction-zone earthquake events (e.g., 2011 Tohoku earthquake in Japan) have subjected high-rise buildings to large numbers of lateral cyclic deformations. Concrete-filled steel tube (CFT) columns, which are often utilized in high-rise buildings in Japan, have been studied under lateral demands with a few loading cycles. However, their seismic performance under a larger number of repeated loading cycles is a considerable concern for future seismic events. Moreover, the use of ultra-high-strength steel materials in CFT columns has recently gained popularity. However, studies on CFT columns made using ultra-high-strength steel materials are still limited. In this study, the seismic performance of CFT columns made using conventional steel or ultra-high-strength steel were investigated experimentally under repeated lateral loading cycles. Four cantilever CFT column specimens were tested with a combined constant compressive axial loading and cyclic symmetric lateral loading. Each specimen was tested with two different lateral loading protocols: the conventional protocol with two cycles at each drift amplitude level, and a second protocol with twenty cycles at each amplitude level to represent the lateral drift demand under a long-period ground motion. The effects of the number of loading cycles on the seismic performance of the CFT columns are discussed. Based on the experimental observations, design recommendations are also presented. Moreover, an approach is proposed to estimate the onset of local buckling of the CFT columns under seismic loading.

A comparative study of the effects of calcium alginate capsules on self-healing properties of base and SBS modified asphalt mixtures

Calcium alginate capsules can gradually release healing agent and heal cracks in asphalt mixtures under vehicle loading. However, the current research is focusing on how calcium alginate capsules affect the self-healing abilities of base asphalt mixtures. It is still unclear whether calcium alginate capsules can be utilized to rejuvenate and heal SBS modified asphalt mixture. Through a three-point bending (3 PB)-cyclic compression loading-3 PB test, the effects of calcium alginate capsules on the self-healing characteristics of base and SBS modified asphalt mixtures were examined and compared in this study. Fourier transform infrared spectroscopy (FTIR) and dynamic shear rheometer (DSR) tests were conducted on extracted asphalt binders to study the release behaviors of the capsules within different asphalt mixtures and their regeneration effects on the asphalt binders. The findings demonstrate that under cyclic compression loading, calcium alginate capsules can greatly enhance the strength recovery ratios of base and SBS modified asphalt concretes. The capsules in SBS modified asphalt concrete released the oil more rapidly than in base asphalt concrete probably due to the higher mixing temperature. Both the base and SBS modified asphalts can be rejuvenated by the oil released from the capsules. However, SBS modified asphalt concrete containing the capsules showed lower strength recovery ratios than base asphalt concrete due to lower flow ability of SBS modified asphalt and incapacity of the capsules to repair the broken SBS polymer network.

Reverse total shoulder glenoid component inclination affects glenohumeral kinetics during abduction: a cadaveric study.

Optimal implant placement in reverse total shoulder arthroplasty (rTSA) remains controversial. Specifically, the optimal glenoid inclination is unknown. Therefore, a cadaveric shoulder simulator with 3-dimentional human motion specific to rTSA was used to study joint contact and muscle forces as a function of glenoid component inclination. Eight human cadaver shoulders were tested before and after rTSA implantation. Scapular plane abduction kinematics from control subjects and those with rTSA drove a cadaveric shoulder simulator with 3-dimentional scapulothoracic and glenohumeral motion. Glenoid inclination varied from -20° to +20°. Outputs included compression, superior-inferior (S/I) shear, and anterior-posterior shear forces from a 6° of freedom load cell in the joint, and deltoid and rotator cuff muscle forces. Data were evaluated with statistical parametric mapping and t-tests. Inferior glenoid inclination (-) reduced S/I shear by up to 125% relative to superior inclination, with similar compression to the neutral condition (0°). Superior inclinations (+) increased the S/I shear force by approximately the same magnitude, yet decreased compression by 25% in the most superior inclination (+20°). There were few differences in deltoid or rotator cuff forces due to inclination. Only the middle deltoid decreased by approximately 7% for the most inferior inclination (-20°). Compared with native shoulders, the neutral (0°) rTSA inclination showed reduced forces of 30%-75% in the anterior deltoid and a trend toward decreased forces in the middle deltoid. Force demands on the rotator cuff varied as a function of elevation, with a trend toward increased forces in rTSA at peak glenohumeral elevation. Inferior inclination reduces superior shear forces, without influencing compression. Superior inclination increased S/I shear, while decreasing compression, which may be a source of component loosening and joint instability after rTSA. Inferior inclination of the rTSA glenoid may reduce the likelihood of glenoid loosening by reducing the magnitude of cyclic shear and compressive loading during arm elevation activities, although this may be altered by specific-subject body habitus and motion. These factors are especially important in revision rTSA or glenoid bone grafting where there is already a 3-fold increase in glenoid baseplate loosening vs. primary rTSA.

Axial compressive and seismic performance of GFRP wrapped square RC columns with different scales

The seismic and axial compression behavior of columns wrapped with FRP sheets has been studied experimentally and theoretically over the last two decades. However, most tests and models focused on small-scale columns with/without steel reinforcement. To get better understanding of this strengthening technique and to achieve reliable design approaches for practical applications, further studies should be carried out on full-scale columns with FRP wraps considering the influence of internal steel and column size. Due to such knowledge gaps, this study exhibits experimental results of 17 GFRP wrapped square RC column specimens with side lengths of 350 mm, 495 mm, and 700 mm tested under both monotonic axial compressive load and cyclic lateral load combined with constant axial compression. The results indicate that the FRP confinement effect is highly affected by column size in both axial compression and cyclic loading. Moreover, provisions of three design codes GB50367–2013, GB50608-2020, and ACI440.2R-17 on the axial loading capacity of FRP confined concrete columns are reviewed and verified with the test data. It is suggested that the influence of column size should be further considered in the codes to widen the application range of the present provisions. • 17 column specimens with different scales were tested under two loading conditions. • Failure modes and load-strain relationship were obtained and seismic parameters and strain were analyzed. • Influence of size effect on the performance of FRP enhanced columns were discussed. • Calculation method from three design codes were reviewed and verified.

Auxetics and Other Systems with Unusual Characteristics

Auxetics and Other Systems with Unusual Characteristics

Diagonal compression cyclic testing of unreinforced and reinforced masonry walls

Steel reinforced plasters (SRP) are a traditional strengthening solution of existing masonry structures. SRPs consist of a thin layer of cementitious mortar or concrete (jacket) that incorporates a steel reinforcing mesh tied to a series of steel bent connectors embedded in the underlying masonry. Despite the recent development of more innovative retrofitting methods, SRPs are still widely adopted because of their low costs and effectiveness in terms of improved performance. In the present paper, a comprehensive experimental program on brickwork masonry walls is presented. The results are intended as a contribution to the knowledge of in-plane behavior of masonry strengthened with SRPs. Unreinforced and plastered masonry walls were subjected to cyclic diagonal compression loading under displacement control. Different thicknesses of walls (2 and 3 wythes) and plasters (30 and 50 mm) were selected. The performances of the plastered and non-plastered specimens were analyzed and compared. The results showed that the SRPs increased considerably the performance of the walls in terms of both strength and deformation capacity. The plaster’s thickness had limited effects on the load carrying capacity of the walls, whereas it had a significant effect on their ductility. Finally, the connectors used to tie the steel mesh to the masonry walls played an essential role and avoided large out-of-plane displacements of the plaster layer after its detachment, thus preventing instability phenomena.

Effects of Hygrothermal Aging and Cyclic Compressive Loading on the Mechanical and Electrical Properties of Conductive Composites.

Conductive polymers and their composites have been widely applied in different applications, including sensing applications. Herein, we constructed a conductive composite of polypropylene, carbon black, and multi-walled carbon nanotubes (PP/CB/MWCNTs) to experimentally study its sensing behaviors in a humid thermal environment. The as-synthesized PP/CB/MWCNT composite polymer was immersed in simulated sweat in deionized water at 67 °C. Regarding their electrical and mechanical properties, different experimental parameters, such as cyclic loading and hygrothermal aging, were investigated by recording the mass changes, carrying out strain sensing experiments, and performing dynamic mechanical analyses before and after the immersion test. The results reveal that the filler content improved the rate of water absorption but decreased at higher concentrations of the solution. The sensitivity of the material decreased by up to 53% after the hygrothermal ageing and cyclic loading. Moreover, the sensitivity under cyclic compression loading decreased with an increasing immersion time, qualitatively illustrated by an effective quantum tunneling effect and conducting path model. Finally, hygrothermal aging reduced the composite's glass transition temperature. This reduction was the most significant for specimens immersed in deionized water, ascribed to the moisture absorption, reducing the molecular chain activity.

Investigation of Acoustic Emission of Cracks in Rails under Loading Close to Operational

The paper is devoted to the study of the possibility of detecting cracks in railway rails by the acoustic emission (AE) method. An experimental study of AE signals under cyclic compression loading of rail fragments, which simulates the rail operating load, has been carried out. Fragments of rails without defects, as well as fragments containing pre-grown fatigue cracks, were studied. It was found that AE signals generated by a rail with a crack have higher activity compared to signals from defect-free specimens. It is shown that the AE signals during the loading of defect-free specimens have a short duration and low amplitude and may be caused by the deformation of non-metallic inclusions. The crack presence leads to an increase in the AE hits rate and changes the nature of the distribution of the AE hits amplitudes. It is shown that the crack location has no effect on the reliability of its detection by the AE method. Criteria of crack detection by AE testing are offered as a result of this study.

Small-Animal Compression Models of Osteoarthritis.

The utility of nonsurgical, mechanical compression-based joint injury models to study osteoarthritis pathogenesis and treatments is increasing. Joint injury may be induced via cyclic compression loading or acute overloading to induce anterior cruciate ligament rupture. Models utilizing mechanical testing systems are highly repeatable, require little expertise, and result in a predictable onset of osteoarthritis-like pathology on a rapidly progressing timeline. In this chapter, we describe the procedures and equipment needed to perform mechanical compression-induced initiation of osteoarthritis in mice and rats.

Bi-Stability in Flexure Beams: Introducing a Setup for Experimental Characterization

Bi-stable mechanisms can remain in two positions without a power input or locking system. These mechanisms can achieve large displacements with low energy, requiring power only during switching. However, their design and analysis are challenging due to the non-linear behavior of their flexible members. Researchers commonly use experimental approaches to study and validate bi-stability, which demands efficient and affordable setups. This work presents a versatile and easy-to-fabricate setup to investigate the bi-stable behavior of flexure beams made of styrene plastic. The testing setup is made of laser-cut acrylic connectors and 3D-printed fixtures. The experiments demonstrate that all tested beams are bi-stable and highlight the impact of thickness on their behavior. The critical forces obtained range from 0.0277 N to 5.2724 N between the thinnest and the thickest samples. The distance traveled before snapping increments, with thickness, ranges from 18.78 mm to 32.6 mm. The samples were subjected to a cyclic compressive load and demonstrated a considerable decrement in the critical forces after the first load. Thicker flexural beams present a more significant deformation, causing fractures in some cases after the five loads. Regardless of the thickness, all samples traveled the same total linear displacement of 45 mm. The presented setup demonstrated consistency and rapidness in experimental bi-stability characterization, with the styrene plastic flexure beams proving to be suitable for studying bi-stability.

Investigating the Effect of Relative Humidity on the Mechanics and Dynamics of Open‐Cell Polyurethane Auxetic Foams

This work describes a series of investigations carried out on sets of pristine and auxetic (negative Poisson's ratio (NPR)) open‐cell polyurethane foams subjected to relative humidity (RH) conditioning ranging from 9% to 92% at room temperature. The foams have been produced using a uniaxially thermoforming process. Pristine and auxetic foams have then been subjected to quasi‐static compressive cyclic loading (with maximum strains of 10% and 80%, respectively), as well as vibration transmissibility tests with base accelerations up to 2.29 g. Increasing levels of RH do not seem to statistically affect the moduli and PRs of foams subjected to lower maximum strains, however, especially the auxetic foams at higher compressive deformations show a decrease in the stiffness with the increase of the RH. The vibration tests show an increasing trend of the dynamic modulus of the foams with the increase of the RH. The results indicate the complexity of the interaction between foam architecture and absorption/desorption mechanisms occurring inside these porous auxetic materials.

Study on Mechanical Properties and Constitutive Relationship of Concrete Corroded by Hydrochloric Acid under Cyclic Load

Most of the existing studies on acid corrosion of concrete have focused on the mechanical behavior of concrete structures under monotonic load or without load. To investigate the mechanical properties of in-service concrete components under cyclic load in an acid corrosion environment, six groups of concrete prism specimens with different acid corrosion degrees (corrosion duration) were designed and prepared by the accelerated corrosion test method. The monotonic and cyclic axial compression load tests on these specimens were conducted to investigate the effects of corrosion degree on the mechanical properties of concrete specimens. The experimental results indicated that hydrochloric acid corrosion has obvious effects on the failure characteristics and mechanical properties of concrete. The surface of corroded concrete was easier to crack and spall under load, and the concrete spalling area enlarged as the acid corrosion duration increased. The compressive capacity of concrete specimens reduced rapidly with the increase in corrosion duration. The stress–strain envelope curves for concrete with different corrosion duration under cyclic load were essentially similar to that of concrete under monotonic load. The degradation rate of the descending section for the stress–strain curves of corroded concrete under cyclic load was much larger than that under the monotonic load due to the accumulation of internal damage in concrete. The peak strain and ultimate strain of corroded concrete increased significantly with the increase in corrosion duration and enhanced by 55.7% and 77.9%, respectively, compared with the uncorroded concrete, whereas the peak stress and elastic modulus rapidly decreased and reduced by 53.3% and 74.1%, respectively. Moreover, based on the strength degradation depth, the concept of effective bearing cross-sectional area ratio was proposed to characterize the corrosion degree of concrete, and the correction coefficient of descending section for the effective bearing cross-sectional area ratio was introduced to establish the constitutive model of corroded concrete under cyclic load, and the results calculated by this model matched well with the experimental values. The research in this paper can provide the experimental and theoretical basis for seismic life cycle and fatigue redesign of concrete structures in acid corrosion environments or coastal areas.

Aerogel Composites Produced from Silica and Recycled Rubber Sols for Thermal Insulation.

Hydrophobic rubber-silica aerogel panels (21.5 × 21.5 × 1.6 cm3) were fabricated from silica and rubber sols and reinforced with several fiber types (recycled tire textile fibers, polyester blanket, silica felt, glass wool). A recycled rubber sol was prepared using peracetic acid and incorporated for the first time in TEOS-based sol-gel chemistry. The composites exhibited good thermal stability up to 400 °C and very low thermal conductivity, in the superinsulation range when using polyester fibers (16.4 ± 1.0 mW·m-1·K-1), and of 20-30 mW·m-1·K-1 for the remaining fibers. They could also endure cyclic compression loads with near full recovery, thus showing very promising properties for insulation of buildings.

Numerical characterization of sandstone’s mechanical responses under multi-level compressive differential cyclic loading (DCL): A 3D particle-based numerical investigation

The mechanical response of rocks subjected to compressive differential cyclic loading (DCL) with various stress rates is rarely investigated via numerical simulation at the microscopic level. In this study, the behaviour of sandstone is numerically investigated via a 3D particle-based numerical model. A damage model is implemented based on the variation in bond diameter and succeeds in accurately reproducing the stress–strain relations obtained from laboratory tests. Three evolution patterns of bond diameter are used to duplicate the strain rates observed during the laboratory tests. A system similar to AE monitoring is run in simulations, and AE events are recorded, classified, and visualized according to the magnitude of released energy at bond failure. The effect of heterogeneous bond strengths on AE characteristics is discussed. A heterogeneous model is recommended for the realistic reproduction of the onset of cracking as well as stress dependency. A stress rate-induced phase shift in terms of the stress–strain relation is observed in both laboratory tests and numerical simulations. The damping effect is thoroughly considered in the numerical model.

Incidence of Compression-Induced Microinjuries in the Cartilage Endplate of the Spine.

In vitro biomechanical study. This study investigated the incidence of microstructural endplate injuries caused by cyclic compression loading. The covarying effects of joint posture, loading duration, and peak compression variation were assessed. The endplate is physiologically and functionally important for the maintenance of spine health. Despite the ability to radiographically diagnose and classify macroscopic endplate injuries, the mechanical mechanisms of injury initiation and progression remain largely unknown. One hundred and fourteen porcine cervical spinal units were examined. All spinal units were exposed to preconditioning tests, followed by cyclic compression testing that differed by posture (flexed, neutral), loading duration (1000, 3000, 5000 cycles), and peak compression variation (10%, 20%, 40%). Microstructural injuries were examined via immunofluorescence staining for collagen I ( i.e. , subchondral bone) and collagen II ( i.e. , hyaline cartilage endplate). From the 678 acquired images, the incidence of node, avulsion, cartilage, and circumferential pore microinjuries were determined. The distribution of microinjuries between postures, spinal levels, and vertebrae were evaluated along with the associations of incidence and size of injuries with loading duration and variation. The incidence of avulsion injuries was significantly greater in caudal endplates (92%, P =0.006). No other injuries differed between vertebrae ( P ≥0.804) and no significant differences were observed between spinal units ( P ≥0.158). With respect to posture, 100% ( P <0.001) and 90% ( P <0.001) of avulsion and node injuries, respectively, occurred in flexed postures, whereas 82% ( P <0.001) of cartilage microinjuries occurred with neutral postures. Loading duration was significantly associated with microinjury incidence ( P <0.001) and lesion size ( P ≤0.003). Mechanical factors such as posture did not appreciably affect the incidence of endplate injury, but microinjury types were differently distributed between flexed and neutral postures. The duration of compression was shown to have an important role in the incidence of microinjury and lesion size.