Compressive Loading Research Articles

Articular cartilage fatigue causes frequency-dependent softening and crack extension

Soft biological polymers, such as articular cartilage, possess exceptional fracture and fatigue resistance, offering inspiration for the development of novel materials. However, we lack a detailed understanding of changes in cartilage material behavior and of crack propagation following cyclic compressive loading. We investigated the structure and mechanical behavior of cartilage as a function of loading frequency and number of cycles. Microcracks were initiated in cartilage samples using microindentation, then cracks were extended under cyclic compression. Thickness, apparent stiffness, energy dissipation, phase angle, and crack length were measured to determine the effects of cyclic loading at two frequencies (1 Hz and 5 Hz). To capture the fatigue-induced material response (thickness, stiffness, energy dissipation, and phase angle), material properties were compared between pre-and-post diagnostic tests. The findings indicate that irreversible structural damage (reduced thickness), cartilage softening (reduced apparent stiffness), and reduced energy dissipation (including phase angle) increased with an increase in the number of cycles. Higher frequency loading resulted in less reduction in energy dissipation, phase angle, and thickness change. Crack lengths, quantified through brightfield imaging, increased with number of cycles and frequency. This study sheds light on the complex response of cartilage under cyclic loading resulting in softening, structural damage, and altered dynamic behavior. The findings provide better understanding of failure mechanisms in cartilage and thus may help in diagnosis and treatment of osteoarthritis.

Fatigue life prediction method for bolted joints based on equivalent structural stress under tensile–compressive loading

In this study, load amplitude–life (Fa–N) curves were obtained through tensile–compressive fatigue tests of bolted joints. It was observed that the correlation coefficient squared (R2) value of the Fa–N curve with the same geometric and pre-tightening parameters was high, but the R2 value of the Fa–N curve with all the parameters was low, indicating poor correlation and inability to meet the engineering requirements. Therefore, an equivalent structural stress model for the bolted joint was first developed based on a mechanical model with a strict mathematical definition to normalize these Fa–N curves, which considered the bolted joint loads as the input conditions and integrated the geometric and pre-tightening parameters. Subsequently, a classical beam–shell equivalent finite element model of the bolted joint was constructed. The nodal loads in the bolted connection zone were coupled with the forces and moments of the beam element nodes through finite element simulation, and the equivalent structural stress (σs) of the bolted joint was then obtained based on the equivalent structural stress model. Consequently, the equivalent structural stress–life (Ss–N) curve and probabilistic stress–life (P–Ss–N) curve normalized for different Fa–N curves were obtained by fitting the data of σs and N. Lastly, the accuracy of the fatigue life prediction method based on equivalent structural stress was verified by conducting the vibration fatigue test on the bolted joint structure of the subway antenna bracket.

Analytical models for predicting the moment‒rotation relationships of steel hub joints with bolted steel side plates in single-layer wood reticulated domes

A very popular and efficient pattern of joints adopted for wood reticulated domes is steel hub joints featuring end-bearing and bolt-connected wood members (EBBC joints). This type of joint shows clear semi-rigidity, which affects the rigidity and overall stability of the structures. This study developed analytical models for predicting the moment‒rotation curves of EBBC joints, considering the effect of axial compression. Specifically, two models termed the WR and WEP models, were developed assuming rigid and elastic-plastic constitutive behaviour, respectively, of the wood in the compression zone of the joint. A tri-linear model for the lateral force-slip relationship of bolt connections was derived. A formula for calculating the deformation modulus and predicting the shear failure of wood members under local compression was proposed and verified. The moment–rotation relationship of the joint was established with equilibrium and compatibility conditions. The accuracy of the analytical models was verified by comparison with a series of experimental results as well as the parametric study results obtained using a refined finite element model. It was revealed that both the WR and the WEP models can predict the moment–rotation relationships accurately for joints without axial compression, whereas for the case of non-negligible axial compression loads, the WEP model offers more accurate predictions. The analytical WEP model proposed in the current paper provides a versatile tool for general design practice to predict moment–rotation curves for traditional or novel EBBC joints.

Experimental investigation of buckling and post-buckling behaviour of repaired composite laminates under in-plane shear loading

The performance of Ramped Scarf (RS) and Stepped Scarf (SS) repair schemes for highly loaded composite structures has been extensively studied under compressive, tensile, and flexural loadings. However, there is a lack of research on the buckling and post-buckling behaviour of RS and SS repairs under in-plane shear loading, which is critical for aerostructures. This paper addresses this gap by investigating the buckling and post-buckling performance of these repair schemes. Pristine (P) laminates, RS repairs with a scarf angle of 3°, and SS repairs with an overlap step length of 1/60 were manufactured and tested. The quality of the scarf repairs was inspected using artificial intelligence-based machine vision. Mechanical in-plane shear testing was conducted to evaluate the buckling and post-buckling behaviour of P, RS, and SS laminates. The experimental results indicate that RS repairs demonstrated an average of 35 % higher maximum displacement and 12 % higher failure load compared to pristine laminates. SS repairs showed 19 % higher maximum displacement, and 5 % higher failure load compared to pristine laminates. RS repairs excelled in all key mechanical performance indicators, including buckling load, Hooke's stiffness, maximum displacement, and failure load, compared to SS repairs. The failure modes of P, RS, and SS laminates were similar. However, RS repairs exhibited greater susceptibility to repair patch detachment compared to SS repairs.

Computing the pressure of agricultural tractors on soil and mapping its compaction

Manufacturers of agricultural machines, when designing, pay a little attention to its impact on soil, thus producing models with high compression loads on the soil or with a small contact area between the tyres/tracks and the soil surface. Therefore, the aim of this study is to evaluate the negative impact of both wheeled and tracked agricultural tractors on the soil, in terms of soil compaction, and its causes (i. e. design features of tractor tyres/tracks), during the last six decades (i. e. from 1961 to 2021). Soil compaction is caused by the pressure applied by agricultural machines on the soil through the contact area of their tyres/tracks with the soil surface. So, the main indicator of the negative impact on the soil by the tractors manufactured during the last 60 years, i. e. the average pressure applied by the tyres or tracks of tractors manufactured in EU and in the post-Soviet cuntries from 1961 to 2021 to the soil, was computed. A general decrease of the average pressure of the tyres/tracks on the soil can be observed in 1980s and 1990s, followed by its general increase since 2000, above all for the tractors having power higher than 140 kW. Thus, there is an urgent need to assess spatial and temporal changes in soil vulnerability to compaction, that depends on weather conditions and soil properties, as well as agricultural management practices, and can only be fully assessed by means of a combination of traditional techniques (i. e. use of soil cone penetrometer followed by 2D mapping using GIS or 3D mapping through geostatistics) and mechanical approaches (i. e. computation of agricultural machine parameters – soil contact area). The results show that tractor manufacturers did not take care of reducing soil compaction during the considered period.

Study of Structural Defects Evolution in Fine-Grained Concrete Using Computed Tomography Methods

Introduction. When studying composite materials for construction purposes, it is needed to consider the mechanisms of formation of the structure and properties of modern concretes in the process of strength development. In studies of modern composite materials based on cement binder, there is no information about the development of structural defects and destruction of the material at the initial stages of strength development. This information can be obtained using X-ray computed tomography, a promising method of nondestructive testing of the state of the material. Therefore, the objective of this work was to study the formation and propagation of cracks in samples of fine-grained concrete with different fractional composition of sand due to natural processes of cement shrinkage, as well as the mechanics of destruction of samples of modified fine-grained concrete when applying a compressive load at the early stages of strength development. Materials and Methods. The study used fine-grained concrete mixtures of three compositions with different sand gradation. The tomography samples were made by placing fresh mixtures in polymer cylindrical containers. Tomography of the samples immediately after manufacture, as well as after 8 and 51 days, was performed in a YXLON Cheetah microfocus X-ray machine. The composition with two-fraction sand was modified by mechanical activation of the components, 20×20×20 mm cube samples were made. Further, compression tests were performed at the Instron installation after 3 and 7.5 hours, and then — tomography of the destroyed samples.Results. It was established that the destruction of contact zones depended on the ratio of the size of the fractions. In the presence of a bulk of coarse sand grains in concrete, the destruction of contact zones was more pronounced and had a main mode. When using fine or polyfraction sand, contact zones were destroyed locally and had a visually smaller area. The images of the destroyed modified sample, tested 3 hours after manufacturing, showed clear cracks and indents on the edges, which indicated the elastic-plastic nature of the destruction. In 7.5 hours, the edges of the sample upon destruction were covered with a network of small cracks; inside the sample there were also numerous cracks and microcracks, which indicated brittle fracture. Based on the obtained images of the deformed structure of modified concrete, the mechanism of transition from elastic-plastic destruction of the material to brittle one was clearly visible.Discussion and Conclusion. The studied dependences of the influence of the size of fine aggregate on the mechanisms of formation and propagation of structural defects contribute to the theory of the processes of destruction of fine-grained concretes. The results obtained prove the prospects of using X-ray computed tomography as a method of nondestructive testing of the internal structure of fine-grained concrete, including at the early stages of strength development.

3D printed concrete incorporating waste rubber: Anisotropic properties and environmental impact analysis

The recycling and reuse of solid wastes mark the construction industry's development towards sustainable and green technologies. 3D printing technology using recycled solid materials is in great demand for intelligent and low-carbon construction. This paper incorporates crumb rubber (0–1 mm) into the printing ink and analyses the fresh and hardened properties. The results showed that the flowability was positively correlated with rubber ratio but negatively with fiber content. R40F15 (40% rubber and 1.5% fiber) obtained the optimal flowability for 3D printing, which remained above 15 mm for 30min. The compressive strength peaked when incorporating 1.5% fiber, while the flexural strength reached the bottom. X direction generated the highest compressive strength in the whole anisotropic tests, followed by the Y and Z directions. The highest strengths of 1.5% and 2.0% fiber content were 69.45 MPa and 64.5 MPa, incorporating 20% rubber. Thus, surfaces anticipated to bear higher loads in compression should be aligned with the X-axis or, at a minimum, avoid alignment with the Z-axis for optimal structural performance. Y direction obtained the highest flexural strength in all anisotropic tests when incorporating 1.5% fiber. Results from digital image correlation test supported that fiber tended to agglomerate in the Y direction. Besides, the environmental analysis was conducted in this paper to quantitively calculate the impacts of all raw materials to the environment.

Free vibration and transient response of initially compressed CNT-reinforced composite plates

This paper investigates the linear free vibration and nonlinear transient response of carbon nanotube (CNT)-reinforced composite plates subjected to pre-existent compressive load in thermal environments. CNTs are reinforced into matrix according to uniform and functionally graded distributions. The properties of constitutive materials are assumed to be temperature-dependent while the effective properties of nanocomposite are determined using an extended rule of mixture. Governing equations are established within the framework of classical plate theory incorporating von Kármán nonlinearity and initial geometrical imperfection. Analytical solutions of deflection and stress function are assumed to satisfy simply supported boundary conditions, and Galerkin method is applied to obtain a time differential equation including both quadratic and cubic nonlinear terms. Fourth-order Runge–Kutta numerical integration scheme is employed to determine dynamical deflection-time response of nanocomposite plates. Numerical analyses are presented to consider the influences of CNT volume fraction, CNT distribution, initial compressive load, geometrical imperfection, elevated temperature and plate geometry on the natural frequencies and nonlinear dynamical response of nanocomposite plates. The study reveals that the natural frequency and dynamical deflection are strongly decreased and increased when initial compressive load is increased, respectively. Numerical results also find that the natural frequencies are enhanced and dynamical deflection is dropped as a result of increase in volume percentage of CNTs, respectively.

The effect of a soft active back support exosuit on trunk motion and thoracolumbar spine loading during squat and stoop lifts

Back support exosuits aim to reduce tissue demands and thereby risk of injury and pain. However, biomechanical analyses of soft active exosuit designs have been limited. The objective of this study was to evaluate the effect of a soft active back support exosuit on trunk motion and thoracolumbar spine loading in participants performing stoop and squat lifts of 6 and 10 kg crates, using participant-specific musculoskeletal models. The exosuit did not change overall trunk motion but affected lumbo-pelvic motion slightly, and reduced peak compressive and shear vertebral loads at some levels, although shear increased slightly at others. This study indicates that soft active exosuits have limited kinematic effects during lifting, and can reduce spinal loading depending on the vertebral level. These results support the hypothesis that a soft exosuit can assist without limiting trunk movement or negatively impacting skeletal loading and have implications for future design and ergonomic intervention efforts.

Microstructure evolution and mechanical response of hetero-induced SiCp addition in Al-6061 under high strain rate compressive loading

Al/SiC composites having a high-volume fraction of SiC are eye-catching materials in the automobile and aerospace industries. However, their behavior under stringent environments i.e., under high strain rate compression is much different than quasi-static compression. For such conditions, the morphology, interfacial bonding, and the fraction of the SiC play a decisive role in achieving the high performance of the Al/SiC composites. Here, in this study, we reported that a transitional effect of de-bonding and intergranular crack in SiC has occurred in Al–SiC composites having SiC particle size >0.7 μm. Below the 0.7 μm, the diffusion of the Al dislocations is characterized on the boundary of SiC along with the strong interfacial bonding. To prove it, we have fabricated an Al6061/30 vol% SiC composite through powder metallurgy route and subsequently subjected to compression in the range of strain rate 0.001–2100 s−1. In support of our observations, the microstructure was characterized by optical microscopy, scanning electron microscopy, X-ray diffraction, electron backscattered diffraction, and transmission electron microscopy analysis. The result also revealed a positive strain rate sensitivity up to a strain rate of 1800 s−1, while for 2100 s−1, the flow stress decreased, which is the cause of adiabatic temperature rise, dynamic recrystallization in Al, and massive cracks and deboning in coarse SiC particles. We also characterized that the SiC having particle size 1–4 μm showed stacking fault and dislocation induced in the SiC due to strong interfacial bonding. A quantitate analysis of dislocation was also established by using the Williamson-Hall technique which further confirmed the dislocation activity and dynamic recrystallization in 2100 s−1, characterized by EBSD and TEM. Thus, this study enables our understating that using the fine SiC particles is promising for achieving the high performance of the Al/SiC composites for use in stringent environments.

Experimental investigation on mechanical properties of the sandwich structure with orthogonal corrugated core reinforced by polyurethane foam

AbstractThe aim of this paper is to explore the effect of polyurethane foam filler on the out‐of‐plane compressive property and low‐velocity impact resistance of the orthogonal corrugated sandwich panel by experimental method. The results show that foam filling increases the energy absorption and specific energy absorption of the orthogonal corrugated sandwich panel by 64.75% and 38.22% under compressive load, respectively. Furthermore, during compression, the filled foam causes the core strut undergo pure buckling failure and gradually folds rather than brittle fracture. Under low‐velocity impact, the strengthening effect of foam filling on the first peak load of the load–displacement of the orthogonal corrugated sandwich panel decreases with the increase of impact energy, while the inhibition effect on the impactor drop increases with the increase of impact energy. The results can provide a reference for the design and optimization of foam‐filled hybrid sandwich structures.Highlights The compressive property and low‐velocity impact resistance of the foam‐filled orthogonal corrugated sandwich panel are tested. The effect of foam filling on the mechanical properties of the orthogonal corrugated sandwich panel is obtained by comparing the out‐of‐plane compressive response and low‐velocity impact response of the empty and foam‐filled orthogonal corrugated sandwich panel and foam sandwich panel. Foam filling can improve the load‐bearing property and energy‐absorbing capacity of the orthogonal corrugated sandwich panel and make it more stable progressive damage.

Mechanical response analysis of asphalt microstructure under tensile and compressive loading based on finite element methods

This study investigates the micro-mechanical response of asphalt microstructure under tensile and compressive loads using atomic force microscopy (AFM) and digital image processing (DIP). AFM captured images of asphalt surface morphology, and DIP extracted geometric information on microstructures such as bee structures, peri phase, and interstitial structures. Five finite element models were created in ABAQUS to simulate their load-bearing capacities and stress-strain distributions under 1 % and 5 % tensile and compressive strains. The results showed minimal differences in load-bearing capacities among the five models under identical strain loads. However, compressive load-bearing capacity was significantly higher than tensile load, with the asymmetry becoming more pronounced as the load increased. Under 1 % compressive strain, the external load was about 3 % higher than under tensile strain, increasing to 36 % higher under 5 % strain. The bee structure exhibited the smallest stress distribution, while the interstitial structure showed the largest. The average maximum stress in the interstitial structure was 1.2 times that of the bee structure, with stress concentration observed at the interface between the peri phase and interstitial structure. The interstitial structure experienced the smallest strain distribution, while the bee structure endured the highest tensile or compressive strain, with the average maximum strain of the bee structure being approximately 1.25 times that of the interstitial structure. Under compressive loads, the maximum stress and strain on the asphalt surface exceeded those under tensile loads, with the difference averaging around 10 % higher. As the proportion of the peri phase increased, stress and strain distribution became more uniform, alleviating stress concentration phenomena. This study provides a potential method for analyzing the mechanical response of asphalt microstructure. The results deepen our understanding of the complex relationship between asphalt microstructure and its micro-mechanical response. Additionally, they suggest possible directions for improving asphalt performance through microstructure adjustment.

New 3D petal-like structures with lightweight, high strength, high energy absorption, and auxetic characteristics

A novel type of petal-like structure that exhibits superior mechanical properties, was proposed and fabricated by integrating advantages of metamaterial, multi-stage deformation, and high strength of fiber-reinforced composites. Compression testing and finite element analysis were first conducted on three petal-like structures formed with different angles and made from fiber-reinforced composites. The findings indicated that these composite-based multi-cell structures can also exhibit a satisfactory stress plateau stage through judicious structural design. After ensuring the structures' performance under quasi-static compression load, the impact resistance of the new structures was further examined. It was found that the structure's auxetic characteristics diminished under low-speed impact load. However, under a 20 J impact load, the structures exhibited energy absorption characteristics (SEA) that surpassed those of both conventional and other new auxetic structures by 8–40 times. These promising results demonstrate that the newly designed petal-like structures have high potential applications in various fields such as construction and automotive industries.

Study on the Damage Characteristics of Wheat Kernels under Continuous Compression Conditions.

Peeling wheat yields higher-quality flour. During processing in a flaking machine, wheat kernels undergo continuous compression within the machine's chamber. As this compression persists, damage to the kernels intensifies and accumulates, eventually leading to kernel breakage. To study the damage characteristics of wheat kernels during peeling, this study established a continuous damage model based on Hertzian contact theory and continuous damage theory. The model's accuracy was validated through experiments, culminating in the calculation of critical parameters for wheat peeling. This study focused on different wheat varieties (Ningmai 22 and Jichun 1) and kernel sizes (the thicknesses of the small, medium, and large kernels were standardized as follows: Ningmai 22-2.67 ± 0.07 mm, 2.81 ± 0.07 mm, and 2.95 ± 0.07 mm; Jichun 1-2.98 ± 0.11 mm, 3.20 ± 0.11 mm, and 3.42 ± 0.11 mm). Continuous compression tests were conducted using a mass spectrometer, and critical damage parameters were analyzed and calculated by integrating the theoretical model with experimental data. The test results showed that the average maximum crushing force (Fc) for small, medium, and large-sized kernels of Ningmai 22 was 96.71 ± 2.27 N, 110.17 ± 2.68 N, and 128.41 ± 2.85 N, respectively. The average maximum crushing deformation (αc) was 0.65 ± 0.08 mm, 0.68 ± 0.13 mm, and 0.77 ± 0.17 mm, respectively. The average elastic-plastic critical pressure (Fs) was 50.21 N, 60.13 N, and 59.08 N, respectively, and the average critical values of elastic-plastic deformation (αs) were 0.37 mm, 0.38 mm, and 0.39 mm, respectively. For Jichun 1, the average maximum crushing force (Fc) for small-, medium-, and large-sized kernels was 113.34 ± 3.15 N, 125.28 ± 3.64 N, and 136.15 ± 3.29 N, respectively. The average maximum crushing deformation (αc) was 0.75 ± 0.11 mm, 0.83 ± 0.15 mm, and 0.88 ± 0.18 mm, respectively. The average elastic-plastic critical pressure (Fs) was 58.11 N, 64.17 N, and 85.05 N, respectively, and the average critical values of elastic-plastic deformation (αs) were 0.45 mm, 0.47 mm, and 0.52 mm, respectively. The test results indicated that during mechanical compression, if the deformation is less than αs, the continued application of the compression load will not result in kernel crushing. However, if the deformation exceeds αs, continued compression will lead to kernel crushing, with the required number of compressions decreasing as the deformation increases. If the deformation surpasses αc, a single compression load is sufficient to cause kernel crushing. Since smaller wheat kernels are more susceptible to breakage during processing, the peeling pressure (F) within the chamber should be controlled to remain below the average elastic-plastic critical pressure (Fs) of small-sized wheat kernels. Additionally, the kernel deformation (α) induced by the flow rate and loading in the chamber should be kept below the average elastic-plastic critical deformation (αs) of small-sized wheat kernels. This paper provides a theoretical foundation for the structural design and optimization of processing parameters for wheat peeling machines.

IMPACT OF HOLLOW CORE DIAMETER AND BFRP WRAPPING ON AXIAL COMPRESSIVE STATIC PERFORMANCE OF TIMBER

This paper presents an experimental study on the axial compressive static performance of the cylindrical timber-wrapped basalt fiber reinforced polymer (BFRP). Beech and black pine woods were used as cylindrical timber material, polyurethane (PUR) adhesive was used as the adhesive agent, and BFRP was used as fiber-reinforced polymers (FRP). The stress on compression tests was applied to 70 pieces of test samples prepared. The results showed that there was found out that the highest average stress value of 51.8 MPa was achieved inthe black pine cylindrical timber- BFRP wrapping- hollow core (Ø=70 mm)- the beech cylindrical timber blocks- BFRP wrapping samples under compression loading. The lowest average value stress value of 30.78 MPa was found in the black pine cylindrical timber- none hollow core samples. On average, the stress of the black pine cylindrical timber- BFRP wrapping- hollow core (Ø=70 mm)- the beech cylindrical timber blocks- BFRP wrapping samples were68% higher than the stress of the black pine cylindrical timber- none hollow core samples. The influence of the hollow core diameter and the BFRP wrapping type were found statistically significant.

Behavior of backfill material made of high-water material and recycled concrete lumps for highwall mining

The highwall mining technique is the family member of green mining system, for which the development of the cost-effective backfill material is always the critical issues to be accounted for. In the present research, an innovative backfill material made of the high-water material and recycled concrete lumps was introduced. A total of 42 specimens with variable configurations were prepared and tested to evaluate the effects of the water-to-powder of the high-water material and particle size of concrete lumps on the compressive behaviour of the developed backfill material. Both the acoustic emission (AE) and the digital image correlation (DIC) instruments were applied to investigate the progressive failure modes of tested specimens in parallel. Test results revealed that the high-water material cemented recycled concrete present an ideal ductility when it is subjected to the uni-axial compressive loading, which is different from normal backfill materials featured with brittleness in natural. It also suggested that the effect of the water-to-power ratio of the high water material is much more obvious than that of the lumps size on the enhancement of deformation ability. In terms of the peak strength, these specimens with the 20 mm to 35 mm lumps is higher than that of its counterparts, which suggested that the lump size is one of the most important factor during the design of the proposed backfill material. Moreover, the peak strength of specimens with the small water-to-powder ratio (i.e., 0.75) surpasses those with ratios of 1.0 and 1.25 by 20.4 % and 29.5 %, respectively. Although the specimens with smaller water-to-powder ratio of high water material exhibited the higher compressive strength, it should be noted that the reduced flowability of which will affect the casting process in turn. Research outcomes obtained from this study is expected to facilitate the wide application of the highwall mining.

Influence of Direct Coronal Restoration Materials on the Fracture Resistance of Endodontically Treated Premolars: An In Vitro Study.

(1) Background: The long-term survival of an endodontically treated tooth depends on a successful root canal treatment as well as an adequate definitive coronal restoration. This study aimed to evaluate the strength of endodontically treated premolars with mesial-occlusal-distal (MOD) cavity preparation restored with different direct coronal restoration materials but from the same manufacturer against fracture. (2) Methods: sixty intact premolars were selected and placed into five groups (n = 12): G1-intact teeth, G2-endodontic treatment and unrestored MOD cavities, G3-endodontic treatment and MOD cavities restored with Tetric PowerFlow and Tetric EvoCeram, G4-endodontic treatment and MOD cavities restored with Multicore Flow and Tetric EvoCeram, and G5-endodontic treatment and MOD cavities restored with Multicore Flow. The specimens were subjected to an axial compression load at a speed of 1.6 mm/min and optically inspected before and after with a stereomicroscope. For each premolars group, the following data were recorded: the compression resistance, the compressive strength, and the maximum force supported. The microstructure of the samples after the compression test was analyzed using scanning electron microscopy (SEM). (3) Results: statistical analysis (ANOVA and Tukey test) showed that there was a statistically significant difference between G1 and the other groups. Even though there was no statistically significant difference between the restored groups, a better mechanical behavior was registered within the G3. (4) Conclusions: this in vitro study indicated that none of the materials used can lead to a higher or at least similar fracture resistance as the intact teeth. The coronal restoration only with nano-hybrid composites may lead to a higher therapeutic benefit for the fracture-susceptible premolars.

Stiffness properties of regular p-bars tensegrity prisms under the compressive loading

The regular tensegrity prisms are a kind of fundamental unit, which can be formed into different configurations by different splicing approaches to achieve specific structural functions. Taking regular prisms as the research object, this article presents an analytical method for structural deformations under compressive loading. The structural parameters after loading can be obtained directly by solving the nonlinear force density equation, which simplifies the form-finding process. This article also studies the structural stiffness under different connection modes. By defining the twist angle change rate and internal force utilization rate, we can compare the relative deformation of different tensegrity prisms. The results show that the relative deformation of the three-bar prism is minimal, and it has the best stiffness.

A biomimetic chiral auxetic vertebral meta-shell

Abstract The work presents a novel thin-walled biomimetic auxetic meta-shell for patient-specific vertebral orthopedic implants. The proposed design stemmed from the concept of an intrinsically multiple curved auxetic meta-structure, which is created by folding a 2D bio-inspired chiral geometry according to the morphology of human vertebral cortical bones. Through a multi-view stereo Digital Image Correlation (DIC) system, we investigated the mechanical response of a bio-grade titanium (Ti6Al4V ELI) additively manufactured prototype of the meta-structure under compressive loadings. In addition, we analyzed the morphology of the prototype using a scanning electron microscopy (SEM) and an optical image dimension measurement system both before and after compressive tests. An accurate Finite Element model, which exactly reproduced the geometry of the 3D printed meta-shell, was implemented and calibrated against experimental results, obtaining a precise prediction tool of its mechanical response. The findings of this work demonstrate that the designed meta-shell shows a peculiar auxetic behavior, a targeted stiffness matching to that of human vertebral bone tissues and a higher global elastic strain capability compared to those of monolithic traditional vertebral body replacements.


Investigating Static and Dynamic Behaviors in 3D Chiral Mechanical Metamaterials by Disentangled Generative Models

AbstractChiral mechanical metamaterials with engineered asymmetric structures have garnered significant interest owing to their potential for manipulating mechanical waves and unconventional mechanical properties. Although several design methodologies have made significant strides in the design and discovery of chiral mechanical metamaterials, 3D designs that incorporate multiple mechanical characteristics remain largely unexplored and the static and dynamic properties of these structures have not received sufficient attention. Here, an innovative approach is introduced for the inverse design of 3D chiral mechanical metamaterials with desired static and dynamic properties, leveraging streamlined shapes to enable a versatile design. By employing conditional generative adversarial networks (c‐GANs), the desired mechanical properties are targeted by focusing on both wave attenuation and stress distribution under compression and shear loading. 3D chiral mechanical metamaterials with additive manufacturing are fabricated to demonstrate the performance of the proposed c‐GAN. Experimental investigations show that the generated structures exhibited a wide range of wave attenuation properties, low stress concentrations, and a variety of stress‐strain curve profiles including nonlinear stiffness, demonstrating their effectiveness in achieving the desired mechanical characteristics. This research offers significant advancements in the on‐demand design capabilities of metamaterials and their applications.