Tensile Stiffness Research Articles

Competition of systematically optimized deep neural networks for the estimation of tensile behavior of aluminum-magnesium alloy

Aluminum-magnesium (Al-Mg) alloys are prevalently employed within the aerospace sector. This research engaged a suite of deep learning approaches, encompassing the Artificial Neural Network (ANN), Gated Recurrent Unit (GRU) networks, Long-Short Term Memory (LSTM), and simple Recurrent Neural Network (RNN) to evaluate their predictive efficacy regarding the tensile strength and stiffness of Al-Mg alloys obtained from molecular dynamics simulation. The Taguchi method was initially applied to refine the architecture of each deep neural network (DNN), followed by a comparative analysis of their optimized configurations. The findings of this investigation revealed that the refined simple RNN and LSTM models exhibited superior predictive accuracy for estimating the strength and stiffness of the alloy, respectively. Moreover, the study elucidated that DNNs equipped with memory capabilities outstripped traditional ANNs in forecasting the tensile properties of Al-Mg alloys.

Insights into the hexamine-assisted ZnO based-MOFs formation on PET fabric for improved self-cleaning, flame retardant, and hydrophilic properties

Organo-metallic frameworks (MOFs) have attracted much attention in the last decade due to their large pore size, large surface area, selective adsorption of small molecules, and optical or magnetic responses in the presence of guest molecules. Particularly, the use of MOFs on textile products through in situ synthesis leads to special properties in a simple method. Here, the polyester fabric was first activated by alkali hydrolysis and then the ZnO-based MOFs were synthesized to obtain a fabric with multifunctional features. FESEM images and EDX elemental analysis showed the presence of MOF particles and zinc, nitrogen, and hydrogen on the polyester surface. The weight of the treated samples increased however the water spreading time decreased due to the polar groups of the MOFs creating higher hydrophilic properties. The presence of hydroxyl and amine groups on the surface of the MOFs-treated polyester was confirmed by FTIR spectroscopy. The final fabric showed photocatalytic self-cleaning, and UV protection properties. In addition, TGA, ash percentage, and burnt length results demonstrated the flame-retardant properties. The tensile strength, thickness, and stiffness of the MOFs-treated fabrics also increased. Finally, the hexamine-assisted ZnO-based MOFs on the polyester surface improve its properties and usability.

Barium titanate exposure on metallographic and mechanical performance of coir fiber made low‐density polyethylene composite

AbstractTechnological growth and biodegradable waste natural fibers are significant choices in polymer matrix composite preparation because of their distinct qualities from monopoly matrix. During the fabrication process, the natural fiber faces poor compatibility and lack of adhesive behavior, resulting in reduced tensile strength and stiffness of the composite. The theme of the research is expanding the mechanical behavior of low‐density polyethylene (LDPE) composite by the exposure of sodium hydroxide‐treated coir fiber (CF) and barium titanate (BaTiO3) through an injection molding route. Influences of CF and BaTiO3 on metallographic, tensile, flexural, and impact strength and microhardness of LDPE composite are evaluated, and its outcomes are compared with mono LDPE. The surface morphology of the developed composite is exposed to homogenous dispersion of BaTiO3 with effective adhesive bonding with CF, which facilitates superior mechanical properties. The LDPE hybrid composite consists of 30 wt% CF and 2.5 wt% of BaTiO3 and is exploited about 69 ± 1.5 MPa of tensile strength, 54 ± 0.5 MPa of flexural strength, 4.9 ± 0.01 J of impact energy, and 31 ± 1.5HV of microhardness, this is greater than the mono LDPE (unreinforced). The enriched LDPE hybrid composite is suggested for automotive dashboard applications.

Regression modelling strategies for projected and sustainable kraft pulping of wheat straw

The demand for paper and paper-based packaging has seen a massive increase in past years, resulting in accelerated deforestation to meet the rising demand, negatively impacting the environment, and there is a need to look towards different non-woody raw materials. Kraft pulping (KP) is widely used in paper making, for which the chemical dose, temperature, time, and energy required must be optimized, for which many insignificant experimental trials are performed. An effort is made to solve this problem by developing the regression equations with the help of Excel using One Factor at a Time Analysis (OFAT), followed by carrying out design of experiments (DoE) using orthogonal approach and regression analysis in Minitab software. Life cycle Assessment (LCA) using the Open-LCA software estimates the effect of chemicals and energy required during pulping on human health, ecosystem quality, and resource depletion. Using regression analysis, the equations for predicting kappa number, yield (%), total energy consumed, and mechanical properties of the paper sheet showed a good fit with an R2 value in the range of 0.90–0.99. Apart from that, the mechanical properties, namely tensile index (41.43 Nm/g), tear index (6.96 mN m2/g), bending stiffness (0.5 mN m), and burst index (3.92 kPa m2/g) of the unbeaten sheet, were determined experimentally at optimized conditions. Based on the Open-LCA result, the optimized pulping conditions had less impact on human health, ecosystem quality, and resource depletion. Industries can use the model to predict the values of kappa number, yield, mechanical properties, and energy consumption without performing optimization experiments that may impact the industry's economy to a greater extent.

Review on Fundamental Considerations During Lignocellulosic Fiber Characterization in Light Micromechanical Analysis of Their Composites

Lignocellulose fibers (Cellulosic fibers) are among the major agricultural resources from plant whose potentials are not exploited in some cases and/or underexploited in many cases. If their potentials for industrial application could be exploited, selling the fibers for manufacturing uses would be a win-win situation for both the industries and the farmers, and provide the latter with a much needed source of additional income since composite material reinforced with lignocellulose fibers can be used for diverse application including the production of parts in automotive industry. For this to be successful, it is mandatory to make fiber level characterization. In this process, there are various determinants that affects the characteristics of lignocellulose fiber including agro-ecological zone, plant age from which the fiber is extracted, lignocellulose structure, fiber extraction method and subsequent treatment to enhance properties. This review, therefore, presents the basics of lignocellulose fiber potential and insight into selected deliberation related to fiber level characterization in light of micromechanical analysis for new biocomposite under development. Included in this review, there are considerations to be potted during characterization at fiber level. For fiber diameter measurement and estimation, the following considerations are reported in this paper: measurement method validation, proper cross-section and fiber geometry assumption, lignocellulose structure and internal holes; enough sample consideration, incorporation of analytical method for cross checking. Likewise consideration during estimating fiber density, single fiber tensile strength and stiffness are review and discussed in this review.

Effect of wet-dry history on performances of dense asphalt mixture: Experimental investigation and predicting model

Asphalt pavement experiences various wet-dry histories in the service stage. However, the influence of wet-dry history on asphalt mixture is unknown. Therefore, to clarify the performance degradation mechanism and predict the performance of asphalt mixture under the action of wet-dry history, the creep-recovery test, indirect tensile stiffness modulus test and indirect tensile strength test were conducted at different temperatures. The finite element method was adopted to analyze the moisture diffusing profile inside the specimen after wet-dry cycles. A moisture damage model considering the soaking time and repeated characteristics was developed to predict the damaged properties. Results show that wet-dry cycles cause a slight mass loss of asphalt mixture. Wet-dry cycling action leads to the increment in high-temperature deformation, and reductions in stiffness modulus and tensile strength. The increase of high-temperature deformation is primarily caused by viscoplastic component. Even if the soaking time is short, high moisture damage occurs while the wet-dry cycle is sufficient. Numerical simulations show that the moisture concentration profiles inside asphalt mixture vary under different wet-dry histories, leading to variations in the damage zone. The degree of damage is also closely related to the acting time of moisture. The critical immersion time of the dense asphalt mixture (about 43 hours) was determined in this study. When the immersion period is shorter than the critical immersion time, the strength loss is greater than the modulus. On the contrary, the degree of modulus damage is higher than that of strength. Considering the actual rainfall climate in China, the strength damage of the on-site asphalt mixture in the field predominates. The proposed model could reflect the weakening trends of modulus and strength. It has good universal applicability in predicting the damaged Marshall stability, modulus, and strength at different temperatures.

Biocomposite Anchors Have Greater Yield Load and Energy Compared With All-Suture Anchors in an In Vitro Ovine Infraspinatus Tendon Repair Model

PurposeTo compare tensile fatigue and strength measures of biocomposite and all-suture anchors in an ovine humerus-infraspinatus tendon model of rotator cuff repair. MethodsInfraspinatus tendons on adult ovine humeri were sharply transected at the insertion. One of each pair was randomly assigned for fixation with two biocomposite or all-suture anchors. Constructs were tested with 200 cycles of 20-70 N tensile load and gap formation was measured at the incised tendon end every 50 cycles. They were subsequently tested to failure. Outcome measures including fatigue stiffness, hysteresis, creep and gap formation, and tensile stiffness, and yield and failure displacement, load, and energy were compared between anchors. ResultsBiocomposite anchors had higher yield load (134.1 ± 6.5 N, p<.01) and energy (228.6 ± 85.7 J, p<.03) than all-suture anchors (104.7 ± 6.5 N, 169.8 ± 85.7 J). Fatigue properties were not different between anchors, but stiffness and gap formation increased and hysteresis and creep decreased significantly with increasing cycle number. ConclusionsWhile the yield displacement of both anchors was within the range of clinical failure, the tensile yield load and energy of ovine infraspinatus tendons secured to the humerus with two single-loaded all-suture anchors in a single row were significantly lower than those secured with two biocomposite anchors in the same configuration. Clinical RelevanceIt is important to understand the biomechanical properties for selecting anchors for rotator cuff repair. A direct comparison of fatigue testing followed by failure strength of infraspinatus tendon fixation with all-suture and biocomposite anchors could help guide anchor selection and post-operative mobility recommendations.

Heterogeneity characterization of commercial structural papers

Abstract Evaluation of physical and mechanical heterogeneity in commercial paperboards is needed to promote their use in structural applications, especially within the field of packaging. Understanding the range of their behaviors is needed to compete with other materials in the current marketplace and expand in others. This work describes the physical and stiffness heterogeneities of twelve commercial materials using tensile tests in the cross-machine direction and several inverse analyses. The effects of grammage, thickness, and apparent density on tensile stiffness were evaluated in both the linear elastic and nonlinear regimes. Thickness and density provided the best explanation for elastic heterogeneous behavior in most of the materials; local grammage was not the best descriptor for any material. The analyses used here were not able to provide a good explanation of the nonlinear behavior, which was attributed to the development of large shear strains within the materials as they neared failure. This work provides a methodology for additional heterogeneous behavior examinations.

Effect of hybridization on the mechanical performance and cost efficiency of carbon/flax bio‐hybrid composites

AbstractThis research investigates the effects of fiber hybridization on the mechanical performance of carbon/flax bio‐hybrid laminates. The study comprised of manufacturing and analyzing five distinct composite laminates, comprising pure carbon and various carbon/flax configurations with symmetric and asymmetric layups. The laminates were subjected to uniaxial tensile and low‐velocity impact testing at energy levels from 30 to 75 J. Quantitative and qualitative analyses were conducted to assess the damage/failure patterns to determine the changes due to hybridization and stacking sequence. The experimental results revealed that integrating flax layers into different bio‐hybrid configurations significantly influences their strength, stiffness and impact resistance. One of symmetric layups, having uniform distribution of flax layers throughout thickness, demonstrated the most enhanced performance. To facilitate comprehensive comparison, two indices were developed: Composite‐Performance Index (CPI) and Cost‐Effectiveness Index (CEI). These indices indicate that bio‐hybrid configurations, optimally designed with appropriate number of evenly distributed flax layers, can match or surpass performance of pure carbon layup. The study concludes that incorporating flax into carbon fiber laminates can yield substantial benefits in impact performance with slight compromise in tensile strength and stiffness. However, the overall cost efficiency of bio‐hybrid composites is superior, considering both tensile strength and impact performance.Highlights Effect of fiber hybridization on the mechanical performance of hybrid laminates was studied. Carbon/Flax composites exhibited slightly lower tensile strength compared to carbon‐based layup. Symmetric layups with evenly distributed flax layers showed enhanced impact performance. Cost efficiency of bio‐hybrid composites is superior for both tensile and impact performance.

Pre-and post-cyclic behavior of soft ground improved by geogrid-encased granular columns considering clogging effect

A triaxial apparatus was utilized to evaluate pre-and post-cyclic behavior of soft ground improved by geogrid-encased granular columns considering clogging effect. The pre-cyclic behavior of specimens showed that the deformation modulus improvement due to the use of a stiffer encasement would be less noticeable in case of clogged granular columns. It was found that during cyclic loading, the use of geogrid encasement will be effective in reducing cumulative settlements and mitigating the liquefaction potential when its tensile stiffness is large enough. Moreover, the post-cyclic behavior of specimens showed that the use of granular columns (whether encased or non-encased) decreased the dependence of the ground deformation modulus on the CSR changes so that the evaluation of the cyclic-induced ground deformation can be done completely independent of the cyclic loading magnitude. It was also found that the use of an encasement with appropriate stiffness played an important role in minimizing the loss of the strength of the ground stabilized by granular columns after experiencing cyclic loads, especially under large earthquakes and after the occurrence of possible liquefaction.

In-plane mechanical properties of a re-entrant hexagonal and chiral hybrid unit-cell metamaterials

Negative Poisson's ratio (NPR) lattice metamaterials have considerable potential for aerospace, medical treatment, and piezoelectricity applications. However, a metamaterial with a high tensile stiffness in the vertical direction and can achieve substantial displacement in its horizontal direction is lacking. In this work, a novel hybrid unit cell comprising a re-entrant hexagonal cell and a tetra-chiral cell connected in parallel is designed. NPR and tunable stiffness are achieved in such a geometry, which can produce significant deformation in the x-direction and has good tensile stiffness in the y-direction. Based on the Eulerian–Bernoulli beam theory, the mechanical properties of the unit cell are derived. Poisson’s ratio in the xy plane and elastic modulus in the x and y directions are established. Using the finite element (FE) method, we analyzed this hybrid unite cell. Samples with identical geometric variables to those of theoretical models are fabricated by 3D printing. Their Poisson’s ratios and elastic modulus in the x and y directions are tested to verify the theoretical and FE results. Results indicate that the Poisson's ratio of metamaterial is negative. The cell-wall thickness has more influence on elastic properties than the aspect ratio of the cell wall. This study can provide new ideas for the engineering applications of metamaterials.

3D Printing of Double Network Granular Elastomers with Locally Varying Mechanical Properties.

Fast advances in the design of soft actuators and robots demand for new soft materials whose mechanical properties can be changed over short length scales. Elastomers can be formulated as highly stretchable or rather stiff materials and hence, are attractive for these applications. They are most frequently cast such that their composition cannot be changed over short length scales. A method that allows to locally change the composition of elastomers on hundreds of micrometer lengths scales is direct ink writing (DIW). Unfortunately, in the absence of rheomodifiers, most elastomer precursors cannot be printed through DIW. Here, 3D printable double network granular elastomers (DNGEs) whose ultimate tensile strain and stiffness can be varied over an unprecedented range are introduced. The 3D printability of these materials is leveraged to produce an elastomer finger containing rigid bones that are surrounded by a soft skin. Similarly, the rheological properties of the microparticle-based precursors are leveraged to cast elastomer slabs with locally varying stiffnesses that deform and twist in a predefined fashion. These DNGEs are foreseen to open up new avenues in the design of the next generation of smart wearables, strain sensors, prosthesis, soft actuators, and robots.

Dewatering and stress characteristics of stacking geotextile tubes under dry and underwater conditions

By filling and stacking geotextile tubes, cofferdams can be constructed with high efficiency and relatively low economic costs. However, the cofferdam construction at river estuary area may face significant challenges due to the limited time period of tide ebbing (e.g., 4 ∼ 6 h at Qiantang river estuary, Zhejiang, China) and the complexity of construction conditions (e.g., filling and stacking under dry and underwater conditions). First, tensile tests were carried out on the geotextile to obtain the tensile strength and stiffness of the material along the warp and weft, respectively. Subsequently, self-weight and stacking dewatering tests were conducted in a model container under both dry and underwater conditions. During the test, the pore water pressure, the height and strain of geotextile tube, and the volume of water discharge were monitored. Model test data revealed that, using an 80% dewatering degree as the formation criterion, the formation time of a geotextile tube is 4 ∼ 6 times longer for the underwater condition when compared to the dry condition. The earlier the stacking pressure was applied, the greater the final dewatering volume was achieved along with the reduced formation time. However, the early application of stacking pressure rendered higher risk of tensile failure of the geotextile.

Performance evaluation of stone mastic asphalt reinforced with shredded waste E-cigarette butts

The recycling of waste materials in asphalt pavements is pivotal for advancing the road industry, offering numerous environmental, economic, and societal benefits. This study explores the recycling potential of waste electronic cigarette butts (E-CBs) within stone mastic asphalt (SMA) mixtures, serving as a substitute for cellulose fibres and enhancing mechanical performance. Considering the critical role of fibre size in asphalt mixtures, two different E-CB shredding sizes (10 and 15 mm) were selected for examination. Additionally, the influence of the plastic component within E-CBs was investigated. The stabilizing effects of using the shredded E-CBs were evaluated via drain-down tests, followed by a series of standard laboratory tests aimed at assessing physical and mechanical properties. Results demonstrate acceptable drain-down properties, volumetric properties, and moisture susceptibility for the use of all four shredded E-CBs. Among the four mixtures incorporating the waste fibres, the utilization of 15 mm shredded E-CBs without plastic constituents yielded the highest values for indirect tensile strength (ITS) and indirect tensile stiffness modulus (ITSM), coupled with excellent water susceptibility and rutting performance. It can be considered a promising alternative to the traditional cellulose fibre. Larger shredded E-CBs exhibited potential for improving mechanical properties, encompassing cohesion, stiffness modulus, and rutting resistance. Although plastic inclusion can enhance rutting resistance, the higher thermal susceptibility associated with plastic warrants careful consideration. Future research may focus on investigating the fatigue and low-temperature cracking properties, as well as the reinforcing mechanisms of shredded E-CBs in asphalt mixtures using micro-characterization techniques.

Modeling and simulation of anisotropic cross-linked cellulose fiber networks with an out-of-plane topography

Non-woven cellulose fiber networks of low areal density are widely used in many industrial applications and consumer products. A discrete element method (DEM) modeling framework is advanced to simulate the formation of strongly anisotropic cellulose fiber network sheets in the dilute limit with simplified hydrodynamic and hydroelastic interactions. Our modeling accounts for in-plane fiber orientation and viscous drag indirectly by using theories developed by Niskanen (2018 Fundamentals of Papermaking, Trans. 9th Pulp and Paper Fundamental Research Symp. Cambridge, 1989 (FRC) pp 275–308) and Cox (1970 J. Fluid Mech. 44 791–810) respectively. Networks formed on a patterned and flat substrate are simulated for different fiber types, and their tensile response is used to assess the influence of the out-of-plane topographical pattern, specifically, on their stiffness and strength. Sheets with the same grammage and thickness, but composed with a higher fraction of softwood fiber (longer fibers with large diameter), have higher strength and higher strain to failure compared to sheets made from hardwood fibers (short fibers with small diameter). However, varying the fiber fraction produces only an insignificant variation in the initial sheet stiffness. The above simulation predictions are confirmed experimentally for sheets comprised of fibers with different ratios of Eucalyptus kraft and Northern Bleached Softwood Kraft fibers. Sheets with out-of-plane topography show an unsymmetric mass distribution, lower tensile stiffness, and lower tensile strength compared to those formed on a flat substrate. The additional fiber deformation modes activated by the out-of-plane topography, such as bending and twisting, explain these differences in the sheet mechanical characteristics.

Tests and Seismic Response Analysis of Guided-Rail-Type Anti-Tensile Rubber Bearing

When subjected to seismic activity, tall isolated buildings with a high aspect ratio are susceptible to overturning as a result of the failure of rubber isolation bearings under tension. In order to address this issue, a guided-rail tension device (GR) has been developed to enhance the tensile strength of rubber bearings. Furthermore, a novel guided-rail isolation rubber bearing (GR&amp;RB) has been proposed as a potential solution. Quasi-static tests have been conducted to investigate the mechanical properties of the GR, as well as the GR&amp;LNR600 and LNR600. Additionally, numerical finite element analysis has been employed to study the seismic response of the GR&amp;RB under El Centro seismic action in a high-rise building with an aspect ratio of approximately 4. The experimental results suggest that the inclusion of GRs has a limited effect on the horizontal mechanical attributes of rubber isolation bearings. Nevertheless, it simultaneously enhances their tensile strength, demonstrating a significant augmentation of 4.23 times. Moreover, the mechanical behavior of the GR aligns with the Hook model. The numerical analysis suggests that the utilization of GR&amp;RB can mitigate the tensile stress levels of rubber isolators. Furthermore, it is recommended to augment the elastic tensile stiffness of the GR while reducing the open value to enhance the tensile efficiency, with the potential to attain up to 75% efficiency in tensile performance.

Muscle-inspired stiffness-tunable flexible fiber jamming structure for wearable robots *

Soft robotics have found their tremendous application prospects in wearable robots due to the inherent compliance of soft materials when interacting with human bodies. However, the limited load-bearing and output capabilities impeded their application in real world. Variable stiffness design contributes to tackling this problem by enhancing the overall structural rigidity. Nevertheless, most of current jamming-based variable stiffness structures realize their stiffness enhancement by squeezing discrete rigid elements, resulting in the loss of structural compliance in the high stiffness state, which could significantly reduce the deformability and even injure the individuals when utilized in wearable robots. In this paper, we propose a muscle-inspired stiffness-continuously-adjustable flexible fiber jamming (FFJ) structure for soft wearable robots. The FFJ structure can achieve continuous stiffness-variation by controlling the fiber overlapping length, which maintains stretchability even in the high stiffness state. We provide a theoretical model to analyze the mechanical performance of the proposed FFJ structure with different design parameters, and verify the model experimentally. The preliminary results show that we achieved 9 times of stiffness enhancement of the proposed FFJ structure by controlling the vacuum pressure, and the maximum tensile stiffness is 4.1 N mm−1. We further demonstrated the effectiveness of the proposed FFJ structure on wearable robots in three different working scenarios: active finger rehabilitation, active elbow rehabilitation, and passive trunk support. The results show that the FFJ structure was able to provide controllable impedance force for active finger/elbow rehabilitation, and help support the human body during long-term labor. This work broadens the frontiers of soft wearable robots and leads a way to the future design of soft and strong robots and devices.

Structural Design and Mechanical Behavior Investigation of Steel–Concrete Composite Decks of Narrow-Width Steel Box Composite Bridge

Steel–concrete composite decks are commonly employed in narrow-width steel box composite girder bridges to augment their lateral spanning capabilities, while the concurrent omission of longitudinal stiffeners leads to a substantial reduction in the number of components, thereby yielding a structurally optimized bridge configuration. This paper delineates the structural design parameters of a narrow-profile steel box composite girder bridge and assess the mechanical behavior of its incorporated steel–concrete composite deck under static and fatigue loading conditions. To this end, two full-scale segment specimens from the composite bridge decks were subjected to equal amplitude cyclic fatigue tests. The investigation specifically concentrated on the impacts of two types of shear connectors—namely, perforated steel plates combined with shear studs and perfobond rib shear connectors (PBL connectors)—on the static and fatigue performance, including fatigue stiffness, of the steel–concrete composite bridge decks. The results indicate that, under the static bending condition, the composite deck specimen equipped with stud connectors demonstrates superior overall flexural stiffness in comparison to the specimen featuring PBL connectors. Furthermore, the flexural stiffness of the steel–concrete composite specimens experiences a negligible alteration across two million fatigue loading cycles. Upon the completion of two million fatigue loading cycles, the composite deck specimens incorporating the shear connectors composed of perforated steel plates and shear studs exhibit relatively wider crack widths under the static peak load. Both configurations of the steel–concrete composite bridge deck specimens manifest evident interfacial detachment, signifying insufficient tensile pull-out stiffness of the shear connectors. It is recommended to increase the quantity of the shear connectors or select the pertinent types in order to enhance the interface shear resistance.

A Biomechanical Study of Calcaneal Tuberosity Avulsion Fracture: A Comparison Between Three-Screw Versus Two-Screw Fixation Strength.

A calcaneal tuberosity avulsion fracture constitutes a sub-group of calcaneal fractures and it poses a high risk of soft tissue compromise, necessitating urgent reduction and fixation. This fracture was commonly treated with screw fixation, andfixation failure associated with this method has been reported in the literature. In light of this, we tested and compared the strength oftwo-screw(2S) versus three-screw (3S) fixations, where the third screw was fixed from the posterior calcaneal tuberosity towards the anterior process in addition to the two parallel screws. Synthetic calcaneum models were tested with an Instron machine to measure the maximum tensile load and stiffness. The mean maximum tensile loads for 3S and 2S were 455.8 N (SD = 47.4) and 341.0 N (SD = 30.9), respectively, and the difference was statistically significant. The mean stiffnesses for 3S and 2S were 29.2 N/mm (SD = 1.8) and 29.7 N/mm (SD = 2.0), but this difference did not reach statistical significance. Based on our findings, the added third screw increased the pull-out strength and can be inserted percutaneously to minimize soft tissue compromise.

Strain rate-dependent failure mechanics of the intervertebral disc under tension/compression and constitutive analysis

BackgroundThe intervertebral disc exhibits not only strain rate dependence (viscoelasticity), but also significant asymmetry under tensile and compressive loads, which is of great significance for understanding the mechanism of lumbar disc injury under physiological loads. ObjectiveIn this study, the strain rate sensitive and tension-compression asymmetry of the intervertebral disc were analyzed by experiments and constitutive equation. MethodThe Sheep intervertebral disc samples were divided into three groups, in order to test the strain rate sensitive mechanical behavior, and the internal displacement as well as pressure distribution. ResultsThe tensile stiffness is one order of magnitude smaller than the compression stiffness, and the logarithm of the elastic modulus is approximately linear with the logarithm of the strain rate, showing obvious tension-compression asymmetry and rate-related characteristics. In addition, the sensitivity to the strain rate is the same under these two loading conditions. The stress–strain curves of unloading and loading usually do not coincide, and form a Mullins effect hysteresis loop. The radial displacement distribution is opposite between the anterior and posterior region, which is consistent with the stress distribution. By introducing the damage factor into ZWT constitutive equation, the rate-dependent viscoelastic and weakening behavior of the intervertebral disc can be well described.