Load-displacement Graphs Research Articles

Investigation of plastic hinge length in high-ductility reinforced concrete shear walls

In this study, the plastic hinge lengths of reinforced concrete (R/C) cantilever shear walls were analytically determined considering various design parameters. Nonlinear static (Pushover) analyses were conducted on R/C shear wall models and their nonlinear behavior was examined using ABAQUS software. In the study, 72 shear wall models with different parameters were analyzed under the influence of vertical and horizontal loads. Parameters whose effects on plastic hinge length were investigated height/length ratio (Hw/Lw), axial load ratio (N/No), and horizontal web reinforcement ratio (ρsh). The load-displacement graphs of the modelled shear walls were obtained. The plastic hinge height of shear walls was determined according to the heights of the deformations in the concrete and longitudinal steel reinforcement in the section when the shear walls lateral load decreased by 15%. The analytical plastic hinge lengths (Lpz) were determined with respect to the location of the yield occurred at the longitudinal steel reinforcement of the shear wall. The observed plastic hinge lengths (Lp) were determined based on the height of observed the crush as of the foundation top level in the concrete shear wall model. The relationship between the findings of this study and empirical formulas in the literature was determined. It was determined that there is greater closeness between the values obtained from empirical formulas in the literature and the observed plastic hinge length values. It was observed that the plastic hinge length generally increases as the shear span increases. It was observed that the change in ρsh was not a very effective parameter in plastic hinge formation. As the N/No decreases, the plastic hinge length values ​​ generally increase. The Lp/Lpz ratio varied within the range of 0.15-0.50. In addition to ductility (μ) values were determined by using the displacements determined according to both the crushing occurred in the shear wall concrete and the yield observed in the steel reinforcement. The observed that the ductility value depends more on Hw/Lw ratio as N/No ratio decreases.

Numerical Investigation of the Effect of Deltoid Radius on Tensile Load in T-joints

In this study, T-shaped joints were designed from composites with different deltoid radius. For this purpose, carbon fiber woven fabrics were preferred as reinforcement elements. Then, tensile analyzes were performed on these composite T-joints. The effect of the deltoid radius on the maximum tensile load and damage behavior of the structure was examined. As a result of the analyses, fiber tensile-compression damage images occurring in the structure for each deltoid radius were obtained along with the load-displacement graph. The Hashin damage criterion was preferred for damage onset. Material Property Degradation (MPDG) method was used for damage progression in progressive damage analysis. By increasing the deltoid radius from 6 mm to 12 mm, the maximum contact load increased by approximately 10%, and by increasing it to 18 mm, the maximum contact load increased by approximately 20.11%. Fiber compression damage, spread over a wide area on the lower surface of the flange where it does not come into contact with the web, was determined to be the dominant damage type, and it was determined that this damage decreased with the increase of the deltoid radius. it was observed that as the deltoid radius increases, the T-jointed composite structure exhibits more rigid material behavior.

Numerical Simulation of Transverse Crack on Composite Structure Using Cohesive Element

Due to their anisotropic behavior, composite structures are weak in transverse direction loading. produces transverse cracks, which for a laminated composite, may lead to delamination and total failure. The transition from transverse crack to delamination failure is important and the subject of recent studies. In this paper, a simulation of transverse crack and its transition to delamination on cross-ply laminate was studied extensively using a cohesive element Finite Element Method (FEM). A pre-cracked [0/90] composite laminate made of bamboo was modeled using ABAQUS/CAE. The specimen was in a three-point bending configuration. Cohesive elements were inserted in the middle of the 90° layer and in the interface between the 0° and 90° layer to simulate transverse crack propagation and its transition to delamination. A load–displacement graph was extracted from the simulation and analyzed. As the loading was given to the specimen, stress occurred in the laminates, concentrating near the pre-cracked region. When the stress reached the tensile transverse strength of the bamboo, transverse crack propagation initiated, indicated by the failure of transverse cohesive elements. The crack then propagated towards the interface of the [0/90] laminates. Soon after the crack reached the interface, delamination propagated along the interface, represented by the failure of the longitudinal cohesive elements. The result of the numerical study in the form of load–displacement graph shows a consistent pattern compared with the data found in the literature. The graph showed a linear path as the load increased and the crack propagated until a point where there was a load-drop in the graph, which showed that the crack was unstable and propagated quickly before it turned into delamination between the 0o and 90° plies.

Experimental investigation of the effectiveness of strengthening methods in reinforced concrete flat slabs with multiple openings under punching load

In this study, an experimental investigation was carried out to strengthen reinforced concrete flat slabs with multiple openings against punching load via three different strengthening methods. The methods applied in this investigation are (a) shear stud method, (b) textile reinforced mortar (TRM) method, and (c) carbon fiber-reinforced polymer (CFRP) method. Thirthy-eight specimens with dimensions of 2000 mm × 2000 mm x 120 mm were produced, and the study was conducted in four series. The first series, consisting of ten specimens, was selected as the reference series in which strengthening operation was not applied; one specimen was produced as solid (no opening) and the rest with openings. The second series was identical to the first series and strengthened with the shear stud method.The third and fourth series were formed from nine specimens with openings, and each sequence was strengthened by textile-reinforced mortar and carbon fiber-reinforced polymer methods, respectively.The variables planned to be examined in this study were chosen as the presence, the location, the dimension of the openings, and the strengthening type. Load-displacement graphs were obtained for each specimen subjected to concentric monotonic static loading, and by employing these graphs; the essential performance indexes such as ultimate load-carrying capacity, initial stiffness, and energy dissipation capacity of the specimens were calculated. It has been revealed that the size and the position of the openings are effective on the performance indexes of the specimens. Significants increases in the ultimate load-carrying capacity, initial stiffness and energy dissipation capacities of the strengthened specimens are among the main findings of this study. Furthermore, the effectiveness of the strengthening methods was discussed by comparing the performance indexes at the end of the study.

Three-Dimensional Finite Element Modeling of Spray-Applied Pipe Liners Repaired Corrugated Metal Pipes Buried Under Shallow Cover

Corrugated metal pipes (CMPs) corrode over time. To maintain structural performance, deteriorated CMPS must be replaced or rehabilitated. Spray-applied pipe liners (SAPLs) are one of the quickest ways to rehabilitate deteriorated CMPs among other ways. Only a few lab tests and finite element studies from the past have been done on this new method. The calibration of a three-dimensional (3D) full-scale finite element method model using test results obtained at the Center for Underground Infrastructure Research and Education laboratory at the University of Texas at Arlington is covered in this paper. The tests were carried out on circular invert cut CMPs that had been rehabilitated with polymeric SAPLs. To repair the invert-cut CMPs, three different thicknesses were used: 0.25, 0.5, and 1-in. The removal of an 18-in. invert from the intact CMP represented the deterioration of the CMP. A full 3D corrugated model was developed to represent the test setup in the FE model using ABAQUS. To perform the calibration process, the load–displacement curves, earth pressure distribution, and strain around the liner were compared to the test results. The comparison of these parameters showed the capability of the model for verification. The verified FE model was used to generate the load–displacement graphs for other thicknesses and elastic modulus of the liner. In addition, the role of the embedment depth is also considered in the analyses in which the maximum deformation of the rehabilitated pipe has decreased by 58.9% with increasing the burial depth of the pipe from 0.4D (D = external pipe diameter) to 1.0D.

Optimization of Structural Steel Used in Concrete-Encased Steel Composite Columns via Topology Optimization

Concrete-encased steel composite columns are preferred for their exceptional ductility and strength, particularly in high-rise buildings. This research aims to enhance both the strength and ductility of these composite columns by increasing the height of the steel profile. Typically, hexagonal or circular openings, referred to as castellated elements, are incorporated into the steel profile to achieve this height increase. This study employed a topology optimization method to identify the ideal opening shape for the steel profile in concrete-encased steel composite columns. The analysis revealed a sinusoidal-like opening shape, which was then refined for manufacturing. The optimal opening shape was used to increase the height of the existing steel profile, and nonlinear analyses were conducted to evaluate the effectiveness of this new optimized steel profile in concrete-encased steel composite columns. Two concrete-encased steel composite columns were designed: one with the optimal steel profile and the other with a standard steel I profile. ANSYS APDL 19.0 software was used to simulate an experiment based on an existing concrete-encased steel column to validate the nonlinear analysis. The verification analysis demonstrated a remarkable similarity between the experimental and numerical load–displacement graphs, indicating that the numerical analysis was reliable. In the analysis of the composite columns, both axial and lateral forces were applied in the nonlinear analyses. The axial force was applied at 15% of the column’s capacity, while the lateral force was applied until the composite column reached a state of failure. The results of the nonlinear analyses allowed for a comparison of load–displacement curves and the performance of the composite columns. In comparison to the standard steel I profile, the steel profile with the optimal opening shape increased load-carrying capacity by approximately 19% and energy absorption capacity by approximately 24%.

Retrofitting of squat RC column by using TRM strip under axial load

This study investigates the retrofitting of reinforced concrete columns with TRM strips. Seventeen test specimens were produced, and one was chosen as a reference test specimen. Damaged by loading up to 50% of their maximum axial load-carrying capacity test specimens were retrofitted with two different carbon textiles. In addition to the textile type, TRM strip width, strip spacing, and the use of anchors were determined as experimental variables. Maximum bearing capacity, displacement at bearing capacity, initial stiffness, displacement ductility ratio, and energy consumption capacity were calculated using the axial load-displacement graphs obtained from the experimental study. Depending on the obtained results, the effects of experimental variables on the behavior of damaged reinforced concrete columns were interpreted and compared. It has been determined that the retrofitting method presents very successful results. It has been observed that the fan-type anchor, which is rarely used in literature studies, significantly increases the maximum bearing capacity and energy consumption capacity values of test specimens. Finally, the experimental results were compared with those obtained from the numerical models created by the ABAQUS finite element software.

Experimental and numerical study on self-compacting alkali-activated slag concrete-filled steel tubes

This study presents a comprehensive experimental and numerical investigation of axially loaded self-compacting alkali-activated slag concrete-filled steel tubular (ACFST) stub columns. Integrating alkali-activated slag concrete (AASC) with concrete-filled steel tubes (CFST) can yield a novel construction composite material that offers advantageous outcomes for both AASC and steel tube. AASC, an environmentally friendly alternative to traditional concrete, offers improved sustainability, while CFST can provide enhanced structural capabilities. To investigate the performance of ACFST columns, nine different AASC mixtures were designed, each varying in binder content, water-to-binder ratio, Na2O %, and activation modulus. In this study, eighteen ACFST specimens were tested under axial compression, evenly divided into nine circular and nine square CFST sections. A numerical model is developed to evaluate the stress-strain behaviour of confined AASC filled in circular and square steel tubes. The proposed numerical model is first applied to analyse ACFST specimens tested in this study and then used to analyse ACFST specimens tested by another researcher to verify its accuracy. The results, including ultimate load capacity, axial load-displacement graphs, and failure modes obtained from the proposed numerical model, have shown strong agreement with the test results. This suggests that the proposed model can be effectively utilized to predict the axial compressive behaviour of both circular and square ACFST columns.

CHARACTERIZING SPINAL LOAD-DISPLACEMENT BEHAVIOUR USING REPRESENTATIVE COMPONENTS

AbstractObjectivesSpinal stiffness and flexibility terms are typically evaluated from linear regression of experimental data and are then assembled into 36-element matrices. Summarising in vitro test results in this manner is quick, computationally cheap and has the distinct advantage of outputting simple characteristic values which make it easy to compare results. However, this method disregards many important experimental features such as stiffening effects, neutral and elastic zones magnitudes, extent of asymmetry and energy dissipation (hysteresis). Alternatives to the linear least squares method include polynomials, separation of the load-displacement behaviour into the neutral and elastic zones using various deterministic methods and variations on the double sigmoid and Boltzmann curve fits. While all these methods have their advantages, none provide a comprehensive and complete characterisation of the load-displacement behaviour of spine specimens. In 1991, Panjabi demonstrated that the flexion-extension and mediolateral bending behaviour of functional spinal units could be approximated using the viscoelastic model consisting of a nonlinear spring in series with a linear Kelvin element. Nowadays viscoelastic models are mainly used to describe creep and stress relaxation, rather than for cyclic loading. The aim of this study was to conclusively prove the viscoelastic nature of spinal behaviour subject to cyclic loading. Being able to describe the behaviour of spine specimens using springs and dampers would yield characterising coefficients with recognisable physical meaning, thus providing an advantage over existing techniques.MethodsSix porcine isolated spinal disc specimens (ISDs) were tested under position and load control. Visual inspection of the load-displacement graphs from which the principal terms of the stiffness and flexibility matrices are derived suggest that the load-displacement behaviour could be idealised by a nonlinear spring system with damping. It was hypothesised that the contributions arising from non-linear spring-like behaviour and damping could be separated for each of the principal load-displacement graphs.ResultsThe principal elements from position and load control tests were plotted with load on the vertical axis and displacement on the horizontal axis, and a polynomial representing spring force was fitted to the data. This polynomial was subtracted from the experimental data. The remainder - representing damping force - was plotted against displacement and velocity and compared to idealised plots for different types of damping behaviour. Applying this reasoning to the six principal load-displacement plots obtained from stiffness and flexibility tests revealed that four of six exhibit behaviour which is a combination of a nonlinear hardening spring and viscous damper. However, for flexion-extension and mediolateral bending, the damping behaviour is more akin to coulomb damping with viscous influences, characterised by a steep central linear region and near horizontal regions at the extremes. These trends were common amongst all six specimens within the study sample size.ConclusionsThe unique approach described here has allowed the characterisation of the load-displacement behaviour of ISDs in terms of characteristic mass-spring-damper systems. This is an important development which allows experimental findings to be framed in terms of mechanical contributions to a given load-displacement behaviour.Declaration of Interest(b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project.

Study of mixed-mode fracture in functionally graded material using an adaptive phase-field fracture model

This work systematically investigates the mixed-mode fracture propagation in functionally graded materials. The crack trajectory and load–displacement responses were effectively simulated using the mixed-mode phase field approach in combination with an adaptive mesh refinement technique. The mesh refinement is carried out using quadtree decompositions, and the elements with hanging nodes are handled as n−sided polygons. The adaptive implementation is validated by solving benchmark problems from the literature. The adaptive technique demonstrates greater computational efficiency by significantly reducing the number of elements without compromising the accuracy of the solution. This study provides insight into how fracture propagation behavior is influenced by gradient profile, material gradation, crack location, energy release rate, and displacement configuration in uni-directional and bi-directional functionally graded material. Remarkably, it is found that the peak load on the load–displacement graph changes noticeably, and the fracture path remains constant despite variations in the critical energy release rate. Notably, the results show that materials with lower fracture toughness have an early failure when studying a center fractured plate. This thorough examination deepens our understanding of the propagation of mixed-mode cracks and provides insight into improving the analysis and design methodologies for functionally graded materials.

A Study on the Attachment Effect of CFRP Plates to Internal Reinforcements of Curtain Wall Frames Using GFRP

This study is for the development of internal reinforcing materials using fiber-reinforced plastics that can be used for curtain wall frames. The main material of the reinforcement is light and inexpensive GFRP. However, GFRP has characteristics of low elastic modulus and brittle fracture. Therefore, CFRP is attached to supplement the disadvantages. In this study, a flexural experiment was performed to confirm the performance improvement effect of GFRP reinforced with CFRP. The results of the flexural experiment showed that the total flexural stiffness increased by about two times when the carbon fiber reinforced plastic plate was attached compared to the specimen made of a single material of glass fiber reinforced plastic. Also, the pattern of the load-displacement graph was found to reflect the characteristics of the ductile material. However, it was observed that adhesion failure first occurred on the attachment surface before the member yielded. Therefore, it was determined that it was necessary to increase the adhesive strength or set the minimum length in order to prevent poor adhesion when manufacturing actual stiffeners. Therefore, in this study, additional specimens were prepared using the specimen length, adhesive strength, and adhesive rate as variables, and then the experiment was conducted. As a result of the experiment, the maximum load decreased in the long specimen, but the overall stiffness was similar, and adhesive failure did not appear conspicuously before the member was destroyed. In the case of adhesive strength, the case using epoxy was more stable than the specimen using resin, and the maximum load and stiffness were slightly higher when the adhesive width of carbon fiber reinforced plastic was the whole.

BIOMECHANICAL STUDY COMPARING THE DOUBLE-LASSO LOOP TECHNIQUE TO INTERFERENCE SCREW FIXATION FOR BICEPS TENODESIS IN AN OVINE MODEL

This study aims to compare the biomechanical properties of the “Double Lasso-Loop” suture anchor (DLSA) technique with the commonly performed interference screw (IS) technique in an ex vivo ovine model.Fourteen fresh sheep shoulder specimens were used in this study. Dissection was performed leaving only the biceps muscle attached to the humerus and proximal radius before sharply incised to simulate long head of biceps tendon (LHBT) tear. Repair of the LHBT tear was performed on all specimens using either DSLA or IS technique. Cyclical loading of 500 cycles followed by load to failure was performed on all specimens. Tendon displacement due to the cyclical loading at every 100 cycles as well as the maximum load at failure were recorded and analysed. Stiffness was also calculated from the load displacement graph during load to failure testing.No statistically significant difference in tendon displacement was observed from 200 to 500 cycles. Statistically significant higher stiffness was observed in IS when compared with DSLA (P = .005). Similarly, IS demonstrated significantly higher ultimate failure load as compared with DSLA (P = .001). Modes of failure observed for DSLA was mostly due to suture failure (7/8) and anchor pull-out (1/8) while IS resulted in mostly LHBT (4/6) or biceps (2/6) tears. DSLA failure load were compared with previous studies and similar results were noted.After cyclical loading, tendon displacement in DLSA technique was not significantly different from IS technique. Despite the higher failure loads associated with IS techniques in the present study, absolute peak load characteristics of DLSA were similar to previous studies. Hence, DLSA technique can be considered as a suitable alternative to IS fixation for biceps tenodesis.

Progressive failure analysis of U-notched thin composite plates repaired with a double-sided composite patch

In this study, carbon fiber-reinforced U-notched composite plates were repaired with composite patches made of the same material using adhesive bonding and their mechanical performance was investigated experimentally and numerically. Repairs were made by applying a double-sided composite patch to the notched thin composite plates. The repaired composite plates were tested under tensile load. The effect of the variation in notch width and depth on the repaired plate failure load and type was investigated. At the end of the experiments, load–displacement graphs of each specimen were obtained. The effect of variation in notch depth and width in the repaired specimens was not as dominant as in the non-repaired specimens. While the variation in notch dimensions changed the failure load between 34% and 37% in the non-repaired specimens, this rate was between 18% and 21% in the repaired specimens. In the numerical analysis, progressive failure analysis was performed using the Hashin Failure Criteria. Subroutine codes were written in the program Ansys, which uses the finite element method for numerical analysis. In the results, numerical and experimental load–displacement graphs and failure types of the specimens are presented comparatively. The convergence rate of the experimental and numerical data was between 92% and 99.8%.

Comparison of strengthening methods to improve punching behavior of two-way RC flat slabs

Within the scope of this study, three different strengthening methods have been proposed to increase the punching strength of reinforced concrete (RC) flat slabs. These methods are a shear stud, fiber-reinforced polymer (FRP), and textile-reinforced mortar (TRM). Ten large-scale RC flat slabs were produced to investigate the effectiveness of strengthening methods. One of these was chosen as a reference, one strengthened with shear stud, four strengthened with FRP and the rest with TRM. Reinforcement type (shear stud, FRP, and TRM), strip direction (straight and diagonal), and anchor usage were determined as experimental variables. The ultimate load capacity, initial stiffness, and energy dissipation capacity values were calculated and compared using the load-displacement graphs obtained as a result of the tests of specimens. According to the experimental results obtained, TRM, FRP, and shear stud methods increased the ultimate load capacity by an average of 58%, 52%, and 20%, respectively. These increased values for energy dissipation capacity are 118%, 63%, and 47%, respectively. In the numerical part of the study, the experimental study was simulated with the ABAQUS/Explicit FEM program, and the obtained results were compared with the experimental results. Moreover, the stresses and damage distributions in the specimens were evaluated. As a result of the study, it was seen that the method applied using textile reinforced strips gave the most successful results among three different strengthening techniques applied to improve the behavior of RC slabs under the effect of punching loading.

Fracture toughness of conventional, milled and 3D printed denture bases

ObjectivesThe aim of this study was to determine and compare fracture toughness (KIC) and work of fracture (WOF) of a conventional (C) denture base, using the notchless triangular prism (NTP) specimen KIC test, with CAD/CAM (milled, M) and 3D-printed (P) materials at 7 d and 90 d. MethodsLucitone 199 (C), Lucitone 199 CAD (M) and Lucitone Digital Print (P) (Dentsply, USA) were used to fabricate NTP specimens. Samples were stored in 37 °C water for 7 d (20/group) and 90 d (20/group) and conditioned in 23 °C water for 1 h prior to testing. For testing, samples were secured in custom-made jigs and loaded in tension until crack arrest/failure. The maximum-recorded load was used to calculate KIC. The results were analyzed by two-way ANOVA, Scheffé multiple mean comparisons (α = 0.05), independent t-tests and Weibull. WOF (in KJ/m2) was calculated by dividing the area under the load-displacement graphs by twice the corresponding crack-arrested cross sectional area of the fractured surfaces. ResultsThe results have shown that: 1) the tested materials had significantly different KIC (P > C > M; p < 0.005) and WOF at both 7d and 90d; 2) ageing in 37 ºC water for 90 d resulted in a significant decrease of KIC in the C and M groups (p < 0.001) and of WOF in all groups. SignificanceThe tested P denture base exhibited significantly higher KIC and WOF, suggesting that it could be more resistant to crack propagation than the C and M materials tested. Water storage for 90 d significantly decreased KIC of C and M materials and WOF of all.

Numerical modelling of mode-I cracking in asphalt concrete

This paper presents a numerical model to simulate mode-I fracture in asphalt concrete. The phase field method is used to simulate diffuse damage in asphalt concrete. In addition to the displacement degrees of freedom, a scalar damage degree of freedom is added at each node of a finite element. Evolution of the damage variable is governed by a crack potential which regularizes a sharp crack over a finite volume. The phase field method does not suffer from mesh dependency problem like the continuum damage models and therefore preferred for damage analysis. A single edge notch beam is analysed to show the performance of the model. The damage pattern as well as load versus crack mouth opening displacement graph is compared with the experimental data. The numerical results show good agreement with the experimental observations.

A proposed strut efficiency factor for strut-and-tie design of steel fibre-reinforced concrete

Strut-and-tie model (STM) is a lower-bound plastic theory to achieve force equilibrium. It uses a simplified truss analogy method to define the load transfer mechanism in the disturbed region (D-region) in concrete structures. STM was mostly applied in the design of conventional reinforced concrete (RC), and there were few discussions on the use of STM for newer concrete technology, e.g., steel fibre-reinforced concrete (SFRC). SFRC presents opportunities in reducing web reinforcements in serviceability checks and in improving the ductility of D-regions. In this paper, a strut efficiency factor for STM is proposed for the design of SFRC by collecting a database of SFRC deep beams. It was discovered that the strut efficiency factor best fits with a function of the product of the fibre factor and concrete cylinder compressive strength. Baseline deep beam numerical models were developed and calibrated with the experimental load-displacement graphs collected through literature. A parametric study with variables such as concrete cylinder compressive strengths, fibre volumes and strut angles were investigated. The proposed strut efficiency factor was found to have a peak capacity lower than the ultimate load capacity computed in the calibrated numerical models, which justified the safe use of STM as a lower-bound plastic method in SFRC.

Non-linear analysis of one-way concrete slabs with carbon-fibre-reinforced polymer strips

Finite-element (FE) models of one-way spanning reinforced concrete slabs strengthened with carbon-fibre-reinforced polymer (CFRP) strips were constructed and analysed. The slabs, which had different-sized openings at different locations, were tested by the authors in a previous study. During the FE analysis, the effective failure modes were taken into account and the behaviour of the concrete–CFRP strip interface was modelled using a non-linear cohesive zone material model. The results of the FE analysis and experimental data were compared in terms of the ultimate load capacities of the slabs, load–displacement graphs, stress distributions and failure modes. The modelled results were found to be consistent with the experimental findings. The yield and ultimate shear force capacities, the yield and ultimate displacements and the yield stiffness of the slabs were calculated with average errors of 11.4%, 6.3%, 27.1%, 13.8% and 24.2%, respectively. After verification of the FE model, analyses of four additional slabs, not previously experimentally tested, were performed. An equation between the ultimate load capacity of a slab and opening size was developed based on the modelling results.

Effect of patch dimension and fiber orientation on non-linear buckling of hybrid composites

AbstractIn this study, first circular hole layered hybrid composite plates were repaired by wet patch method, and then buckling behavior was investigated experimentally and numerically. In the experimental study, composite plates were produced by vacuum infusion method using hybrid fabrics made of carbon and aramid. Circular holes were drilled in the produced plates and then these holes were repaired with the same material. In the wet patch repair method, wet hybrid fabrics impregnated with epoxy resin were placed around the hole and then this area was subjected to pressure and temperature by vacuum infusion method. In experimental tests, pressure force was applied to the fixed sides and force-displacement graphs were obtained. In a numerical study, non-linear buckling analysis was performed by creating numerical models of plates and patches using the finite element method. As a result, experimental and numerical load-displacement graphs were obtained in accordance with pre- and post-buckling. Thanks to the repair in accordance with practical applications, no interface debonding damage occurred in ideal samples. Increasing the patch length from 30 mm to 40 mm increased the maximum damage load by 6 %, while increasing the patch length to 50 mm increased damage load by 12 %. Increasing the patch thickness from 0.65 mm to 1.1 mm increased the load by 67 %, while increasing it to 2.16 mm increased the load to 247 %. Fiber orientation was found to be a more influencing factor in critical buckling and damage load than the ply sequence.

Effect of artificial surface shapes and their malpositioning on the mechanics of the replaced ankle joint for possible better prosthesis designs

BackgroundThe clinical outcomes of total ankle replacement are limited by prosthesis component malpositioning during surgery. The goal of this study is to assess the mechanical impact of this malpositioning in a validated computer model. MethodsIn a previously developed multi-body dynamic model of the human ankle complex three different artificial implants were designed, each one presenting a different approximation of the natural articular surfaces of the corresponding specimen. The most common implant translational and rotational malpositionings were defined and mimicked. Dynamic simulations of joint motion were run for the various surfaces and malpositionings. The same input loading conditions derived from a previous in-vitro experiment on the corresponding natural specimen were applied. FindingsFrom load-displacement graphs it was observed that all three artificial surfaces reproduced well physiological motion between the calcaneus and the tibia/fibula, with a maximum difference of 2°. It was found that antero-posterior translation of either the tibial or the talar component and inclination of the tibial component in the sagittal plane led to considerable increases in the range of motion. Antero-posterior and dorsiflexion of the tibial component resulted in an increased internal-external rotation by up to 3.5° and 4.0°, respectively. The corresponding increase of inversion-eversion was 5.0° and 6.5°. InterpretationThis study showed that relatively small surgical errors have great consequences in replaced joint mechanics. The present model can be used in future studies to analyse the effect of malpositioning with any specific current total ankle prosthesis.