Axial Torsion Research Articles

Regional variations of mechanical responses of IVD to 7 different motions: An in vivo study combined with FEA and DFIS

The abnormal mechanical behaviour of a lumbar intervertebral disc (IVD) is commonly recognized as a direct indicator of intervertebral disc degeneration (IDD). However, current methods cannot evaluate the patient-specific mechanical performance of an IVD in vivo during movement. This study establishes a patient-specific (PS) model that combines the kinematics parameters of the lumbar spine obtained with a dual fluoroscopic imaging system (DFIS) and a finite-element (FE) method for the first time to reveal the mechanical behaviours of IVDs in vivo under seven motions. Three healthy participants were recruited for this study. CT images were obtained to create finite-element models of L3-L5 spine segments. Meanwhile, participants were required to take specific positions including upright standing, flexion, extension, left and right lateral bending, as well as left and right axial torsion in the DFIS. The in vivo kinematic parameters, calculated by registering the CT images with images obtained with DFIS, were considered as loading conditions in FE simulations. Significant differences of von Mises stresses and principal strains were found between PS model and GN model which employing a generalized moment as loading conditions, former resulting in up to 76.74 % lower strain than the GN model. Also, considerable differences were observed for five anatomical regions of the IVD (L3-L5). Under all motions, the stress in the centre region (nucleus pulposus) was the lowest, while the stress in the posterior region was the highest in extension motion. Therefore, activities such as stretching with an extension, should be avoided by patients with a herniated disc, in which the posterior region was the herniation site. The PS model combining in vivo kinematics and FE simulations shows the potential in the design and assessment of patient-specific implants.

Magneto-viscoelastic rod model for hard-magnetic soft rods under 3D large deformation: Theory and numerical implementation

The main purpose of this work is to develop a three-dimensional (3D) viscoelastic rod model for hard-magnetic soft (HMS) rods under large deformation which are widely used active structures in soft robotics. To do so, the Simo’s viscoelasticity theory has been rationally incorporated into the geometrically exact 3D curved rod model. The proposed model includes the deformation modes of axial tension, shear, bending, and torsion, which is applicable to the HMS rods with arbitrarily initial curved and twisted geometries under 3D large deformation. The viscoelastic constitutive equations of the HMS rod in the present formulation are formulated, which include the general relaxation functions. To obtain the expression for the magnetic load, the rotation-based magnetic free energy density is introduced, and the governing equations of the HMS rod with magnetic load and body force are presented. To obtain the numerical implementation, an implicit time integration algorithm that simply extends the generalized-α method for the rotation group, and the corresponding variational formulation and its linearization of the rod model are derived. To validate the model, five numerical examples, including 2D dynamic buckling, 3D static, and 3D dynamic problem are presented. The dynamic problems include the dynamic snap-through behavior of a bistable HMS arch and damped oscillation of a quarter arc cantilever under 3D deformation. The simulation results show good agreement with the results reported in the literature.

Finite element analysis of distraction osteogenesis with a new extramedullary internal distractor

Distraction osteogenesis (DO) is a bone regenerative maneuver, which is conventionally done with external fixators and, more recently, with telescopic intramedullary nails. Despite the proven effectiveness, external approaches are intrusive to the patient’s life while intramedullary nailing damages the growth plates, making them unsuitable for pediatric patients. An internal DO plate fixator (IDOPF) was developed for pediatric patients to address these limitations. The objective of this study was to test the hypothesis that the IDOPF can withstand a partial weight bearing scenario and create a favorable mechanical microenvironment at the osteotomy gap for bone regeneration as the device elongates. A finite element model of a surrogated long bone diaphysis osteotomy fixation by means of the IDOPF was created and subjected to axial compression, bending and torsion. As the osteotomy gap increased from 2 mm to 20 mm, under compression, The average axial interfragmentary strains decreased from 2.33% to 0.35%. Stress increased from 179 MPa to 281 MPa at the contact interfaces of the telescopic compartments, which exceeded the endurance limit of stainless steel (270 MPa) but was below its yield limit (415 MPa). These results demonstrate, that the IDOPF can withstand a partial load bearing scenario and provide a stable biomechanical environment conductive to bone healing. However, high contact stresses at the telescopic interfaces of the device are likely to cause wear, as is frequently reported in telescopic fixators. This study is a step towards refining the IDOPF design for clinical use.

A Biomechanical Comparison Study of Plate-Nail and Dual-Plate Fixation in AO/OTA 41-C2 Tibial Plateau Fractures.

This study's purpose was to evaluate the biomechanical performance of plate-nail and dual-plate fixation for the treatment of AO/OTA 41-C2 tibial plateau fractures. Twenty synthetic tibias were selected and randomly divided into a plate-nail group (n = 10) and a dual-plate group (n = 10). After the artificial tibias were osteotomized to simulate AO/OTA 41-C2 tibial plateau fractures in both groups, the plate-nail and the dual-plate methods, respectively, were used for fixation, and then axial compression loading, three-point bending, torsion, and axial failure tests were carried out. The data of each group were recorded and statistically analyzed. In the axial compression test, the average stiffness of the plate-nail group was higher than that of the dual-plate group (p < 0.05). The displacement generated in the plate-nail group was significantly smaller than that in the dual-plate group (p < 0.05). In the resisting varus test, the stress of the plate-nail group was significantly higher than that of the dual-plate group (p < 0.05). In the resisting valgus test, the stress of the plate-nail group was slightly higher than that of the dual-plate group, but the difference was not statistically significant (p > 0.05). In the static torsion test, the load applied to the plate-nail group was smaller than that of the dual-plate group when rotated to 5° (p < 0.05). In the axial compression failure test, the average ultimate load of the plate-nail group was significantly higher than that of the dual-plate group (p < 0.05). The treatment of AO/OTA 41-C2 tibial plateau fractures with plate-nail fixation is superior to that with dual-plate fixation in resisting axial stress and preventing tibial varus deformity, while dual-plate fixation has better resisting torsional ability.

Biomechanical validation of novel polyurethane-resin synthetic osteoporotic femoral bones in axial compression, four-point bending and torsion

In addition to human donor bones, bone models made of synthetic materials are the gold standard substitutes for biomechanical testing of osteosyntheses. However, commercially available artificial bone models are not able to adequately reproduce the mechanical properties of human bone, especially not human osteoporotic bone.To overcome this issue, new types of polyurethane-based synthetic osteoporotic bone models have been developed. Its base materials for the cancellous bone portion and for the cortical portion have already been morphologically and mechanically validated against human bone. Thus, the aim of this study was to combine the two validated base materials for the two bone components to produce femur models with real human geometry, one with a hollow intramedullary canal and one with an intramedullary canal filled with synthetic cancellous bone, and mechanically validate them in comparison to fresh frozen human bone.These custom-made synthetic bone models were fabricated from a computer-tomography data set in a 2-step casting process to achieve not only the real geometry but also realistic cortical thicknesses of the femur. The synthetic bones were tested for axial compression, four-point bending in two planes, and torsion and validated against human osteoporotic bone.The results showed that the mechanical properties of the polyurethane-based synthetic bone models with hollow intramedullary canals are in the range of those of the human osteoporotic femur. Both, the femur models with the hollow and spongy-bone-filled intramedullary canal, showed no substantial differences in bending stiffness and axial compression stiffness compared to human osteoporotic bone. Torsional stiffnesses were slightly higher but within the range of human osteoporotic femurs.Concluding, this study shows that the innovative polyurethane-based femur models are comparable to human bones in terms of bending, axial compression, and torsional stiffness.

Effect of Sextant Fixating Angle of Spiral Clavicle Plate on Biomechanical Stability-A Preliminary Finite Element Study.

A spiral clavicle plate has been accepted for its superior multidirectional compatibility in the treatment of midshaft clavicle fractures from a biomechanical perspective. However, the influence of the sextant angle (spiral level) definition on biomechanical performance has not been clarified. A conceptual finite element analysis was conducted to identify the advantages and drawbacks of spiral clavicle plates with various sextant angle definitions. Conventional superior and three different conceptual spiral plates with sextant angle definitions ranging from 45 to 135 degrees were constructed to restore an OTA 15-B1.3 midshaft clavicle fracture model. Three major loading scenarios (cantilever downward bending, axial compression, and axial torsion) were simulated to evaluate the reconstructed structural stiffness and the stress on the clavicle plate and bone screws. The spiral clavicle plate demonstrated greater capability in resisting cantilever downward bending with an increase in sextant angle and showed comparable structural stiffness and implant stress compared to the superior clavicle plate. However, weakened resistance to axial compression load was noted for the spiral clavicle plate, with lowered stiffness and increased stress on the clavicle plate and screws as the spiral level increased. The spiral clavicle plate has been reported to offer multidirectional compatibility for the treatment of midshaft clavicle fractures, as well as geometric advantages in anatomical matching and reduced skin prominence after surgery. The current study supports that remarkable cantilever bending strength can be achieved with this plate. However, users must consider the potential drawback of lowered axial compression resistance in safety considerations.

The effect of axial–torsion coupling on the compressive collapse behavior of Kresling tubes

The coupled axial compressive and torsional response of thin-walled tubes, having Kresling geometric units in series, with hollow hexagonal cross-sections of similar wall thickness, is studied. The tubes are fabricated using multi-jet fusion technology with Polyamide-12 (PA12) material. Each tube is compressed under displacement-controlled quasi-static loading with roller boundary conditions to eliminate any reaction torque being induced in the tube. The tube’s deformation response is characterized by an initial load rise followed by a drop in the load past a load maximum. This load drop is caused by localized collapse within a single Kresling unit. The collapse mechanism is accompanied by relative rotation between the ends of the Kresling unit, indicating the presence of compression-twist coupling. After local densification in the collapsed Kresling unit is attained, the load rises and attains a peak followed by a second load drop causing the other Kresling unit to collapse. Finite Element (FE) simulations show that the nonlinearity of the material response influences the onset of the collapse of the Kresling unit. Results from the present study will be helpful in tailoring the geometry of the Kresling unit cells to attain desired energy absorption or to “tune” the end-displacement vs. rotation response of the structure.

Nonlinear Slippage of Tensile Armor Layers of Unbonded Flexible Riser Subjected to Irregular Loads

The unbonded flexible riser has been increasingly applied in the ocean engineering industry to transport oil and gas resources from the seabed to offshore platforms. The slippage of helical layers, especially the tensile armor layers of unbonded flexible risers, contribute to the nonlinear hysteresis phenomenon, which is a research hotspot and difficulty. In this paper, on the basis of a typical eight-layer unbonded flexible riser model, the nonlinear slippage of a tensile armor layer and the corresponding nonlinear behavior of an unbonded flexible riser subjected to irregular external loads are studied by numerical modeling with detailed cross-sectional properties of the helical layers, and are verified through a theoretical method considering the coupled effect of the external loads on the unbonded flexible riser. Firstly, the balance equation of each layer considering the effect of external loads is established based on functional principles, and the overall theoretical model of the unbonded flexible riser is set up in consideration of the contact between adjacent layers. Secondly, the numerical modeling of each separate layer within the unbonded flexible riser, including the actual geometry of the carcass and pressure armor layer, is established, and solid elements are applied to all the interlayers, thus simulating the nonlinear contact and friction between and within interlayers. Finally, after verification through test data, the behavior of the unbonded flexible riser under the cyclic axial force, torsion, bending moment, and irregular external and internal pressure is studied. The results show that the tensile armor layer can slip under irregular loads. Additionally, some suggestions related to the analysis of unbonded flexible risers under irregular loads are drawn in the end.

The Effect of Twisted Wire Configuration on the Stability of External Fixator: A Biomechanical Study

The Ilizarov fixator is a type of external fixator that is used to treat patients who have suffered injuries from accidents, bone shortening, or nonunion of the bone. The principle behind the Ilizarov fixator is that thin wires (called Kirschner wires) are used to support the bones and connect them to framed rings. Before being fastened to the rings, the wires are tensioned and drilled through the bones. This study suggests using a new parallel wires configuration at the same level on the same ring and two revised versions, which are divergent and convergent models, and compare them with standard wires, 60 angle wires model. All models were designed using SolidWorks, a computer-aided design (CAD) software, and then analyzed in four conditions (axial compression, medial bending, posterior bending, and torsion) with Finite Element Analysis (FEA) using Ansys Workbench 2020 R2. Mechanical testing was conducted to validate the FEA results, A simple model consisting of a single ring, two K-wires, and polylactic acid (PLA) cylinders was utilized in a tensile test. It has been concluded from the results that the parallel model and its improvement have higher stiffness to axial compression, medial bending, and torsion, but a lower posterior bending stiffness, except the divergent model with 8-hole separation which has a relatively acceptable stiffness for posterior bending.

Analyzing isolated degeneration of lumbar facet joints: implications for degenerative instability and lumbar biomechanics using finite element analysis.

The facet joint contributes to lumbar spine stability as it supports the weight of body along with the intervertebral discs. However, most studies on the causes of degenerative lumbar diseases focus on the intervertebral discs and often overlook the facet joints. This study aimed to investigate the impact of facet joint degeneration on the degenerative changes and diseases of the lumbar spine. A finite element model of the lumbar spine (L1-S1) was fabricated and validated to study the biomechanical characteristics of the facet joints. To simulate degeneration of the facet joint, the model was divided into four grades based on the number of degenerative segments (L4-L5 or L4-S1) and the contact condition between the facet joint surfaces. Finite element analysis was performed on four spine motions: flexion, extension, lateral bending, and axial torsion, by applying a pure moment to the upper surface of L1. Important parameters that could be used to confirm the effect of facet joint degeneration on the lumbar spine were calculated, including the range of motion (ROM) of the lumbar segments, maximum von Mises stress on the intervertebral discs, and reaction force at the facet joint. Facet joint degeneration affected the biomechanical characteristics of the lumbar spine depending on the movements of the spine. When analyzed by dividing it into degenerative onset and onset-adjacent segments, lumbar ROM and the maximum von Mises stress of the intervertebral discs decreased as the degree of degeneration increased in the degenerative onset segments. The reaction force at the facet joint decreased with flexion and increased with lateral bending and axial torsion. In contrast, lumbar ROM of the onset-adjacent segments remained almost unchanged despite severe degeneration of the facet joint, and the maximum von Mises stress of the intervertebral discs increased with flexion and extension but decreased with lateral bending and axial torsion. Additionally, the facet joint reaction force increased with extension, lateral bending, and axial rotation. This analysis, which combined the ROM of the lumbar segment, maximum von Mises stress on the intervertebral disc, and facet joint reaction force, confirmed the biomechanical changes in the lumbar spine due to the degeneration of isolated facet joints under the load of spinal motion. In the degenerative onset segment, spinal instability decreased, whereas in the onset-adjacent segment, a greater load was applied than in the intact state. When conducting biomechanical studies on the lumbar spine, considering facet joint degeneration is important since it can lead to degenerative spinal diseases, including adjacent segment diseases.

The application of inverted lateral clavicle locking compression plate for medial clavicle fractures: biomechanical study and clinical implementation.

There has been no absolute consensus on the optimal implant for fixation of medial clavicle fracture. The purpose of the present study was to test the biomechanical efficacy of inverted lateral clavicle locking compression plate (LCP-LC) in fixation of this specific fracture location by finite element analysis. Transverse and comminuted medial clavicle fracture simulated models stabilized by three different devices including inverted LCP-LC, superior clavicle LCP (LCP-SC), and dual reconstruction (LCP-RP) with LCP-SC were investigated biomechanical performance under three loading conditions, i.e., axial compression, inferior bending, and axial torsion. EQV stress exhibited on implant and elastic strain at fracture site under inferior bending was greater than other loading cases. LCP-SC construct represented the greatest EQV stress and elastic strain. The inverted LCP-LC construct demonstrated lower EQV stress than the LCP-SC construct and was comparable to dual plating. Under axial compression and axial torsion, elastic strain produced from the inverted LCP-LC construct was comparable to dual plating, but greater than dual plating when subjected to inferior bending. By the results of FE analysis, inverted LCP-LC could be a potential application for fixation of clavicle fracture with short medial fragment.

Effect of multiaxial strain amplitudes on the cyclic behavior for SN490B steel under proportional loading

SN490B is used in main steel members of high-rise buildings. In this study, multiaxial cyclic tests were conducted on SN490B under a combination of axial tension, compression, and torsion. For a strain amplitude of εa = 0.3%, cyclic softening behavior was observed regardless of multiaxiality. The cyclic softening converged after approximately 100 cycles. However, no significant cyclic softening was observed at εa = 0.5%. The stress variation is expressed as a function of plastic strain. The stress variation equation developed for the cyclic softening and hardening behavior of SN490B accurately approximated the test results.

Mechanical properties and application of glass fiber reinforced polyurethane composites communication lattice tower

To address the deficiencies in traditional communication towers in mobile communication engineering, such as heavy weight, easy corrosion and poor durability, this study proposes replacing traditional communication towers with GFRP communication lattice towers with lightweight, high-strength and good durability. Firstly, GFRP material test and GFRP circle tube bending capacity test are conducted. The maximum bending moment that can be subjected to the anchorage end of GFRP circular tube is 18.20 kN·m. Finite element analysis of GFRP circular tubes verifies the accuracy of the bending test results. Secondly, a GFRP communication lattice tower with a height of 25 m is designed adopting GFRP circular tubes as tower columns. Through the bending test of the GFRP tower, it is verified that the connection between the columns and web members of the GFRP tower is reliable and the force pattern of the GFRP tower is reasonable. The large deflection theory can be adopted to the displacement of GFRP towers accurately. Thirdly, according to the actual engineering requirements, the finite element analysis of 25 m-high GFRP tower under the basic wind pressure of 0.45 kN/m2 is carried out by using 3D3S (a spatial structure design software). It can be obtained that the vibration mode of the GFRP communication tower shows two forms of lateral bending and axial torsion. 0° wind load direction has the greatest influence on the displacement of the GFRP tower. The stress ratio of each component in the GFRP tower is less than 1, indicating that no damage occurs in the GFRP tower. Finally, GFRP towers have good economic benefits, good environmental performance and wide range of application after comparing the GFRP tower and traditional steel tower. The demonstration project of the GFRP communication lattice tower is established in Qingyuan City, Guangdong Province, China. When subjected to a typhoon with a wind speed of 17.26 m/s, The horizontal displacement of the GFRP tower top is 10 m, which is about 2/5 of the height of GFRP tower. Although the displacement is large, the GFRP tower is still not destroyed. It can be concluded from the research in this paper that GFRP towers have low cost, good mechanical properties, good durability, and wide application range, which can promote the rapid construction of 5 G communication base stations.

Biomechanical analysis of bridge combined fixation system as a novel treatment for the fixation of type A3 distal femoral fractures.

To compare the biomechanical parameters of AO/OTA type A3 distal femoral fractures fixed bilaterally with a bridge combined fixation system (BCFS) and lateral locking compression plate + locking reconstruction plate (LCP + LRP). Twelve A3 distal femoral fracture models with medial cortical defects of the distal femur were created using synthetic femoral Sawbones. BCFS and LCP + LRP were used for bilateral fixation, with six in each group. Axial compression and torsion tests were performed on the two groups of fracture models to determine their stiffness during axial compression and the Torsional stiffness during torsion tests. Axial compression failure tests were performed to collect the vertical loads of the ultimate failure tests. In the test conducted on the fixed type A3 distal femoral fracture models, the axial stiffness in the BCFS group (group A) (1,072.61 ± 113.5 N/mm) was not significantly different from that in the LCP + LRP group (group B) (1,184.13 ± 110.24 N/mm) (t = 1.726, P = 0.115), the Torsional stiffness in group A (3.73 ± 0.12 N.m/deg) was higher than that in group B (3.37 ± 0.04 N.m/deg) (t = 6.825, P < 0.001),and the ultimate failure test of type A3 fracture model showed that the vertical load to destroy group A fixation (5,290.45 ± 109.63 N) was higher than that for group B (3,978.43 ± 17.1 N) (t = 23.28, P < 0.05). Notably, intertrochanteric fractures occurred in groups A and B. In the fixation of type A3 distal femoral fractures, the anti-axial compression of the BCFS group was similar to that of the LCP + LRP group, but the anti-torsion was better.

Finite element analysis comparison of Type 42A2 fracture fixed with external titanium alloy locking plate and traditional external fixation frame

BackgroundAt present, not all Type AO/OTA 42A2 open fractures can be treated by external fixation brackets, not to mention the inconvenience of this technique in clinical practice. External titanium alloy locking plates, which are lightweight and easy-to-operate, can be used as an alternative treatment option for such patients. However, there are few reports of finite element biomechanical analysis on the titanium alloy locking plates and fixation brackets being placed on the medial side of the tibial fracture. In this study, the biomechanical properties of titanium alloy locking plates and fixation brackets for treating Type AO/OTA 42A2 fractures were compared by applying the finite element method, and the results provided data support for the clinical application of the external titanium alloy locking plate technique.MethodsType AO/OTA 42A2 fracture models were constructed using CT data of a male volunteer for two external fixation techniques, namely the external titanium alloy locking plate technique and the external fixation bracket technique, according to commonly-used clinical protocols. Then, the four-point bending, axial compression, clockwise rotation and counterclockwise rotation tests under the maximum load were simulated in finite element analysis software. The stress distribution, peak stress and overall tibial displacement data for the two different external fixation techniques were obtained and compared.ResultsIn the four different test conditions (i.e., four-point bending, axial compression, clockwise torsion, counterclockwise torsion) under the maximum load, the two external fixation techniques showed obvious von Mises stress concentration at the contacts between the screw and tibia, between the screw and titanium alloy locking plate, between the self-tapping self-drilling needle and tibia, between the self-tapping self-drilling needle and the external fixation device, as well as around the fracture end and around the cortical bone at the upper and lower ends of the tibia. The peak stress was ranged 26.67–558.77 MPa, all below the yield stress strength of titanium alloy. The peak tibial displacement of the external titanium alloy locking plate model was smaller than that of the fixation bracket model. In terms of structural stability, the external titanium alloy locking plate technique was superior to the external fixation bracket technique.ConclusionsWhen fixing Type AO/OTA 42A2 fractures, external titanium alloy locking plates are not only lightweight and easy-to-operate, but also have better performance in terms of axial compression, bending and torsion resistance. According to the finite element biomechanical analysis, external titanium alloy locking plates are superior to traditional external fixation brackets in treating Type AO/OTA 42A2 fractures and can better meet the needs of clinical application.

Parameter sensitivity analysis of the axial stability for a marine flexible pipe

Marine unbonded flexible pipes serve as the most essential equipment in offshore oil and gas exploration and exploitation. Axial compressive loads during installation or in service in the complex marine environment usually lead to buckling failure. A flexible pipe is a composite structure with multiple functional layers, of which the tensile armor layer plays a key role with regard to the response of the pipe subjected to axial loads. In this paper, a simplified three-dimensional finite element model is developed, focusing on the tensile layer and replacing the carcass layer, pressure sheath layer, and pressure armor layer by a cylindrical rigid body to reduce computational expense. By using this model, the buckling failure modes of the tensile armor layer (in particular the birdcaging phenomenon) are analyzed. Several key parameters that affect the stability of the flexible pipe under axial compression and torsion are emphasized, and their effects on its axial and torsional stiffness are compared and discussed. The results show that both the lay angle of the steel wires and the interlayer friction coefficient have a significant influence on the axial and torsional stiffness of the pipe, whereas the damaged length of the outer sheath has virtually no effect.

Nonlinear Structural Vibration of Multi-Megawatt Vertical Axis Wind Turbine Blades-Part 1: Derivation of Motion Equations

Replacing fossil fuels with renewable energy is one of the important means to improve energy scarcity and environmental protection, and is of great significance for achieving sustainable development of human society. Vertical axis wind turbine (VAWT) is one of the key equipment for applying green energy — wind energy. During the operation of VAWT, its blades not only have to withstand periodic aerodynamic loads, but also suffer from centrifugal force effects and the Coriolis force effect caused by coupling with multi-dimensional deformation. The complex stress situation makes the blades susceptible to damage, resulting in structural resonance and instability of aeroelastic stability. This paper applies the Euler beam model and Hamilton principle to establish a nonlinear structural vibration motion equation for large-span vertical axis wind turbine blades with fully coupled four-dimensional deformation (i.e. lateral bending deformation, chord bending deformation, axial torsion deformation, and axial tensile deformation), and retains the nonlinear term of the motion equation to the third-order infinitesimal. Separating the motion equation into equilibrium equation and dynamic equation, it can be seen that the displacement of equilibrium state caused by the centrifugal force of the rigid body exists in the form of a coefficient in the dynamic equation, which will have an impact on the dynamic characteristics. This modeling work can provide a research foundation for exploring the dynamic characteristics and aeroelastic stability of VAWT blades in the future.

Comparison of a 2.7-mm and 3.5-mm locking compression plate for ulnar fractures: a biomechanical evaluation.

Implant prominence after ulnar fracture fixation may be mitigated by the use of lower profile plates. The biomechanical strength and stability of 2.7-mm and 3.5-mm locking compression plates for fixation were compared. Two fracture conditions, transverse (N = 10) and oblique (N = 10), were evaluated in an in vitro study. Half of the specimens for each condition were fixed with 2.7-mm plates and the other half with 3.5-mm plates, all fixed with conventional dynamic compression mechanisms. Specimens were loaded under ±2 Nm of cyclic axial torsion, then under 10 Nm of cyclic cantilever bending, and bending to failure. Interfragmentary motion and strain were analyzed to determine construct stability as a function of fracture pattern and plate size. Interfragmentary motion was significantly larger in all constructs fixed with 2.7-mm plates, compared with 3.5-mm plates (P < 0.01). The 2.7-mm constructs with transverse fractures had the greatest motion, ranging between 5° and 10° under axial rotation and 5.0-6.0 mm under bending. Motions were the lowest for 3.5-mm constructs with oblique fractures, ranging between 3.2 and 4.2 mm under bending and 2°-3.5° for axial rotation. For oblique fractures, the bending moment at ultimate failure was 31.4 ± 3.6 Nm for the 2.7-mm constructs and 10.0 ± 1.9 Nm for 3.5-mm constructs (P < 0.01). Similarly, for transverse fractures, the bending moment was 17.9 ± 4.0 Nm for the 2.7-mm constructs and 9.7 ± 1.3 Nm for the 3.5-mm constructs (P < 0.01). Although 3.5-mm plates were more effective at reducing fracture motion, they were consistently associated with refracture at the distal-most screw hole under load to failure. By contrast, 2.7-mm plates plastically deformed despite excessive loads, potentially avoiding a subsequent fracture. Level V.

On the winding pattern influence for filament wound cylinders under axial compression, torsion, and internal pressure loads

An intrinsic characteristic of components manufactured by the filament winding process is a winding pattern formation during the processing. This paper aims at unlocking and understanding how the winding pattern influences the mechanical behaviour of filament wound cylinders under different boundary conditions. To realize this, a series of finite element models followed by an original geometric approach to generate the pattern are herein developed. Four different patterns and six different winding angles are modelled. These are also modelled by varying the number of layers towards understanding whether there is a correlation between the pattern and the number of layers or not. Three loading cases are considered: axial compression, pure torsion, and internal pressure. Key results reveal that the more layers are stacked to the cylinder, the less impactful is the winding pattern to all loading cases herein investigated.

Predicting transformation patterns in pseudoelastic NiTi tubes under proportional axial–torsion loading

We present a comprehensive modeling study on the patterns of propagating instabilities in NiTi tubes under proportional axial–torsion loading. Our study directly refers to the experimental work of Reedlunn et al. (2020), with a particular focus on the unique longitudinal transformation bands that occur in torsion-dominated loading paths. A previously-developed gradient-enhanced model of pseudoelasticity is employed and is adapted to incorporate the residual stresses. In addition, our finite-element setup accounts for the impact of collet grips on the NiTi tubes via a simplified frictional contact model. The results demonstrate the capability of the model in capturing subtle features of the transformation patterns observed in the experiment, including the multi-finger fronts in tension-dominated loading and longitudinal bands in torsion-dominated loading. Our study suggests that the combination of the residual stresses and the collet grips facilitates the formation of longitudinal bands.