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Balanced fiber-reinforced rubber (FRR) pipes not only provide displacement compensation when transporting pressurized media but also prevent additional forces and displacements from being exerted on the connected pipeline system. Investigating the balanced performance of FRR pipes and the axial stiffness of balanced pipes is crucial for optimizing pipeline design and improving the reliability of pipeline systems. This paper develops a numerical model of FRR pipes that considers the nonlinearity of the rubber material and the interaction between the rubber matrix and fiber-reinforced layers. Using this model, the balanced performance of the pipe is calculated, and its axial stiffness under combined internal pressure and axial load is analyzed. Numerical results are compared with experimental data for validation. The results indicate that the pipe's balance is achieved through the combined effects of the elongation and rotation of the reinforcing fibers and the deformation of the rubber matrix, highlighting the significant impact of the rubber matrix on the mechanical performance of the FRR pipe. Furthermore, the pipe's balanced performance and axial stiffness are highly sensitive to the winding angle of reinforcing fibers. The proposed numerical model fills the gap in using numerical methods to evaluate the balanced performance of FRR pipes and provides valuable insights for their design and optimization.

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The article presents the influence of important design parameters of a spiral gasket on axial stiffness and leakage level. These parameters were the angle of inclination of the central part of the spiral section, the length of the vertical part of the spiral section, and the degree of densification of the material filling the metal coils. The scope of work was divided into two stages. In the first, experimental tests were conducted to determine the stiffness and tightness of a standard spiral gasket at two extreme levels of densification of the filler material, and the elastic-plastic properties of expanded graphite, which is the filler material of the metal spirals, were determined. In the second stage, multivariate numerical calculations were carried out to determine the axial stiffness of the gasket and to evaluate the distribution of contact pressure on the sealing surface. A novel aspect of the work is the proposal of a mathematical model to estimate the averaged value of the modulus of elasticity of the filler material as a function of the degree of densification and the execution of an experimental plan that significantly allowed the adoption of a limited number of analysed model variants used in the numerical calculations.

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BACKGROUND: Pedicle screw fixation provides one of the most stable spinal constructs. Their designs together with osseous characteristics have been known to influence the screw-bone interplay during surgical maneuvers and thereafter the fusion process. Various technical modifications to enhance screw performance have been suggested. This study evaluated the pull-out strength and axial stiffness of a novel pedicle screw design with variable thread geometry and pitch. METHODS: The newly designed triple threaded pedicle screw is tapered, and has unique out-turned flanges to hold the cancellous bone and a finer pitch at its distal and proximal end to engage the cortical bone. Five lumbar and 4 lower thoracic cadaveric vertebrae were divided into hemivertebrae. A standard cancellous pedicle screw and the newly designed pedicle screw were inserted into each hemivertebra. Axial stiffness and peak pull-out force between the screw types were compared; a finite element analysis was also performed to additionally compare the pull out under toggle forces. RESULTS: In cadaveric study, the axial stiffness of the new screw was significantly better than that of the standard screw. However, the peak load between the screws was not statistically different. Finite element analyses suggested lesser stress at bone-implant interface for the new screw along with better axial stiffness under both co-axial and toggle forces. CONCLUSIONS: Our novel pedicle screw design with variable thread geometry demonstrates greater axial stiffness compared with the standard screws, and therefore is likely to withstand a greater surgical manipulation.

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Reinforced concrete structures are subjected to frequent maintenance and repairs due to steel reinforcement corrosion. Fiber-reinforced polymer (FRP) laminates are widely used for retrofitting beams, columns, joints, and slabs. This study investigated the non-linear capability of artificial intelligence (AI)-based gene expression programming (GEP) modelling to develop a mathematical relationship for estimating the interfacial bond strength (IBS) of FRP laminates on a concrete prism with grooves. The model was based on five input parameters, namely axial stiffness (Eftf), width of FRP plate (bf), concrete compressive strength (fc'), width of groove (bg), and depth of the groove (hg), and IBS was considered the target variable. Ten trials were conducted based on varying genetic parameters, namely the number of chromosomes, head size, and number of genes. The performance of the models was evaluated using the correlation coefficient (R), mean absolute error (MAE), and root mean square error (RMSE). The genetic variation revealed that optimum performance was obtained for 30 chromosomes, 11 head sizes, and 4 genes. The values of R, MAE, and RMSE were observed as 0.967, 0.782 kN, and 1.049 kN for training and 0.961, 1.027 kN, and 1.354 kN. The developed model reflected close agreement between experimental and predicted results. This implies that the developed mathematical equation was reliable in estimating IBS based on the available properties of FRPs. The sensitivity and parametric analysis showed that the axial stiffness and width of FRP are the most influential parameters in contributing to IBS.

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The role of connecting rod in healing process of a fractured bone has always been of significant importance for surgeons. Adding a connecting rod to the fixator would be a secure option for increasing stability without increasing infection rate. The roles of 4 design parameters of the connecting rod (ie, connecting rod diameter, elevation, material, and configuration) were assessed by using finite element models to calculate axial stiffness and interfragmentary strain at the fracture gap. Taguchi method was used to achieve an optimal design set for maximizing stability with regard to connecting rod variables. Also, analysis of variance (ANOVA) approach was employed to determine contribution percentage of each design parameter on outputs. For optimizing connecting rod design parameters, an optimal set of variables consisting of 11 mm, 40 mm, 200 GPa, and Type 3 external fixator were determined by Taguchi for connecting rod diameter, elevation, modulus of elasticity, and configuration, respectively. However, as Type 3 external fixator stability is a little more than Type 2, it would be better if Type 3 external fixator in Taguchi suggestion be replaced by Type 2 external fixator to be as minimally invasive as possible. Furthermore, ANOVA results revealed that the connecting rod configuration is the most important parameter with 95% and 96% effectiveness on the interfragmentary strain and axial stiffness.

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Highly efficient heat exchange tubes are special tube shapes that are widely used in heat exchangers to enhance heat transfer. In this study, experimental measurements and numerical simulations were carried out on two types of highly efficient heat exchange tubes, namely, spirally grooved tubes and converging-diverging tubes, to investigate changes in their mechanical properties after rolling from smooth tubes. It was found that, unlike the smooth tubes, all axial, circumferential, and radial stresses exist at the two types of tubes under axial loading, and the maximum axial stress is much larger than that at the smooth tubes. Compared to the smooth tubes, the yield strength and ultimate strength of the highly efficient heat exchange tubes increase while the axial elastic stiffness decreases. Although the capability of resisting fatigue fracture of the highly efficient heat exchange tubes is less than that of smooth tubes, they still meet the requirements of the heat exchanger under fatigue loading. Axial stress concentration factors and stiffness equivalent factors for the highly efficient heat exchange tubes are regressed as a function of the structural parameters for engineering applications.

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Loss of sagittal alignment and balance in adult spinal deformity can cause severe pain, disability and progressive neurological deficit. When conservative treatment has failed, spinal fusion using rigid instrumentation is currently the salvage treatment to stop further curve progression. However, fusion surgery is associated with high revision rates due to instrumentation failure and proximal junctional failure, especially if patients also suffer from osteoporosis. To address these drawbacks, a less rigid rod construct is proposed, which is hypothesized to provide a more gradual transition of force and load distribution over spinal segments in comparison to stiff titanium rods. In this study, the effect of variation in rod stiffness on the intradiscal pressure (IDP) of fixed spinal segments during flexion-compression loading was assessed. An ex vivo multisegment (porcine) flexion-compression spine test comparing rigid titanium rods with more flexible polycarbonate-urethane (PCU) rods was used. An increase in peak IDP was found for both the titanium and PCU instrumentation groups as compared to the uninstrumented controls. The peak IDP for the spines instrumented with the PCU rods was significantly lower in comparison to the titanium instrumentation group. These results demonstrated the differences in mechanical load transfer characteristics between PCU and titanium rod constructs when subjected to flexion-compression loading. The concept of stabilization with a less rigid rod may be an alternative to fusion with rigid instrumentation, with the aim of decreasing mechanical stress on the instrumented segments and the possible benefit of a decrease in the incidence of screw pullout.

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OBJECTIVES: External fixators are the traditional fixation method of choice for contaminated open fractures. However, patient acceptance is low due to the high profile and therefore physical burden of the constructs. An externalised locking compression plate is a low profile alternative. However, the biomechanical differences have not been assessed. The objective of this study was to evaluate the axial and torsional stiffness of the externalised titanium locking compression plate (ET-LCP), the externalised stainless steel locking compression plate (ESS-LCP) and the unilateral external fixator (UEF). METHODS: A fracture gap model was created to simulate comminuted mid-shaft tibia fractures using synthetic composite bones. Fifteen constructs were stabilised with ET-LCP, ESS-LCP or UEF (five constructs each). The constructs were loaded under both axial and torsional directions to determine construct stiffness. RESULTS: The mean axial stiffness was very similar for UEF (528 N/mm) and ESS-LCP (525 N/mm), while it was slightly lower for ET-LCP (469 N/mm). One-way analysis of variance (ANOVA) testing in all three groups demonstrated no significant difference (F(2,12) = 2.057, p = 0.171).There was a significant difference in mean torsional stiffness between the UEF (0.512 Nm/degree), the ESS-LCP (0.686 Nm/degree) and the ET-LCP (0.639 Nm/degree), as determined by one-way ANOVA (F(2,12) = 6.204, p = 0.014). A Tukey post hoc test revealed that the torsional stiffness of the ESS-LCP was statistically higher than that of the UEF by 0.174 Nm/degree (p = 0.013). No catastrophic failures were observed. CONCLUSION: Using the LCP as an external fixator may provide a viable and attractive alternative to the traditional UEF as its lower profile makes it more acceptable to patients, while not compromising on axial and torsional stiffness.Cite this article: B. F. H. Ang, J. Y. Chen, A. K. S. Yew, S. K. Chua, S. M. Chou, S. L. Chia, J. S. B. Koh, T. S. Howe. Externalised locking compression plate as an alternative to the unilateral external fixator: a biomechanical comparative study of axial and torsional stiffness. Bone Joint Res 2017;6:216-223. DOI: 10.1302/2046-3758.64.2000470.

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OBJECTIVE: Biomechanical comparison between locked plating and retrograde nailing of supracondylar femur fractures with simulated postoperative weight-bearing. METHODS: The Locking Condylar Plate (LCP) and Retrograde/Antegrade EX Femoral Nail (RAFN) were tested using 10 paired elderly cadaveric femurs, divided into Normal and Low Bone Mineral Density (BMD) groups, with a simulated AO/OTA type 33-A3 supracondylar femur fracture. Each specimen was subjected to 200,000 loading cycles in an attempt to simulate six weeks of postoperative recovery with full weight-bearing for an average individual. The construct's subsidence due to cyclic loading, and axial stiffness before and after the cyclic loading were measured and their correlation with BMD was studied. The two implants were compared in a paired study within each BMD group. RESULTS: LCP constructs showed higher axial stiffness compared to RAFN for both Normal and Low BMD groups (80% and 57%, respectively). After cyclic loading, axial stiffness of both constructs decreased by 20% and RAFN constructs resulted in twice as much subsidence (1.9 ± 0.6mm). Two RAFN constructs with Low BMD failed after a few cycles whereas the matched pairs fixed with LCP failed after 70,000 cycles. CONCLUSIONS: The RAFN constructs experienced greater subsidence and reduced axial stiffness compared to the LCP constructs. In Low BMD specimens, the RAFN constructs had a higher risk of failure.

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10.3969/j.issn.2095-4344.2013.26.011

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Objective To analyze the axial stiffness of human pelvis that were set with the double support standing posture and subjected to gradient vertical loads. Method Nine intact embalmed cadaver specimens were marked from 1# to 9# according to the test sequence, and then subjected to vertical static loads in the gradient of 100 N from 0 N to 500 N. The load displacement data were collected by using the beam sensor of electronic universal testing machine to calculate the axial stiffness of human pelvis. Results The differences of axial stiffness among individual pelvis were large (P=0.815), ranging from 240 N/mm to 776 N/mm. All the pelvic specimens were divided into three groups by cluster analysis (the first group: 1#、2#、3#、5#、9#, the second group: 4#、6#、8#, the third group: 7#). According to the processed results, there were statistical differences among the groups (P<0.05). The trends of pelvic axial stiffness were different under gradient loads. The axial stiffness of the first and third group, totally six specimens, increased with loads increasing; while the axial stiffness of the second group including three specimens increased first, but then decreased with the loads increasing. Conclusions There are significant individual differences in pelvic axial stiffness and its changing discipline within the physiological range; the cluster analysis can be used to analyze the changing discipline between the load and stiffness of human pelvis; as a whole, the pelvic axial stiffness increased with the loads increasing.

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The Ilizarov fixator allows significantly more axial motion at the fracture site than the conventional monofixators. But the transfixing wires have inevitable problems of soft tissue impalement. Therefore the Rancho mounting technique, replacing the transfixing wires with half pins, has become a common place. But the increment of the axial stiffness secondary to replacing transfixing wires with half pins has not been defined clearly yet. The authors measured the axial stiffness of the Ilizarov fixator and two different configurations of the Rancho frame. The group I frame was the Ilizarov fixator composed of four rings and two transfixing wires on each ring. The group II frame was the Rancho frame and it was constructed same as the Ilizarov frame but a transfixing wire was replaced with a half pin from two central rings respectively. The group III frame was another type of Rancho frame which was constructed same as the second group but the remaining transfixing wire was replaced with a half pin from the two central rings respectively. The axial stiffness of the Group I , II and Group III frames were 71.54+/-7.21N/mm, 89.65+/-6.42N/mm, 101.01+/-7.92N/mm respectively. The axial stiffness difference between the Group I frame and the Group II frame was statistically significant(p<0.01). Also the difference between the Group I frame and the Group III frame was statistically significant(p<0.01). This study shows that the replacement of two transfixing wires with two stainless half pins resulted in significant increment of the axial stiffness of the Ilizarov frame.