An analytical, finite element and experimental study of single-lap joints bonded with epoxy adhesive

Analytical and finite element studies on behavior of FRP strengthened RC beams under torsion

BACKGROUND CONTEXTOblique lumbar interbody fusion (OLIF) can provide an ideal minimally invasive solution for achieving spinal fusion in an older, more frail population where decreased bone quality can be a limiting factor. Stabilization can be achieved with bilateral pedicle screws (BPS), which require additional incisions and longer operative time. Alternatively, a novel self-anchoring stand-alone lateral plate system (SSA) can be used, where no additional incisions are required. Based on the relevant literature, BPS constructs provide greater primary biomechanical stability compared to lateral plate constructs, including SSA. This difference is further increased by osteoporosis. Screw augmentation in spinal fusion surgeries is commonly used; however, in the case of OLIF, it is a fairly new concept, lacking a consensus-based guideline. PURPOSEThis comparative finite element (FE) study aimed to investigate the effect of PMMA screw augmentation on the primary stability of a stand-alone implant construct versus posterior stabilization in OLIF with osteoporotic bone quality. STUDY DESIGNThe biomechanical effect of screw augmentation was studied inside an in-silico environment using computer-aided FE analysis. METHODSA previously validated and published L2-L4 FE model with normal and osteoporotic bone material properties was used. Geometries based on the OLIF implants (BPS, SSA) were created and placed inside the L3-L4 motion segment with increasing volumes (1–6 cm3) of PMMA augmentation. A follower load of 400 N and 10 Nm bending moment (in the three anatomical planes) were applied to the surgical FE models with different bone material properties. The operated L3-L4 segmental range of motion (ROM), the inserted cage's maximal caudal displacements, and L4 cranial bony endplate principal stress values were measured. RESULTSThe nonaugmented values for the BPS construct were generally lower compared to SSA, and the difference was increased by osteoporosis. In osteoporotic bone, PMMA augmentation gradually decreased the investigated parameters and the difference between the two constructs as well. Between 3 cm3 and 4 cm3 of injected PMMA volume per screw, the difference between augmented SSA and standard BPS became comparable. CONCLUSIONSBased on this study, augmentation can enhance the primary stability of the constructs and decrease the difference between them. Considering leakage as a possible complication, between 3 cm3 and 4 cm3 of injected PMMA per screw can be an adequate amount for SSA augmentation. However, further in silico, and possibly in vitro and clinical testing is required to thoroughly understand the investigated biomechanical aspects. CLINICAL SIGNIFICANCEThis study sheds light on the possible biomechanical advantage offered by augmented OLIF implants and provides a theoretical augmentation amount for the SSA construct. Based on the findings, the concept of an SSA device with PMMA augmentation capability is desirable.

Buckling of fixed-ended lean duplex stainless steel hollow columns of square, L-, T-, and +-shaped sections under pure axial compression—a finite element study

Elliptical hollow section steel cantilever beams under extremely low cycle fatigue flexural load – A finite element study

A finite element and fatigue threshold study of shelling in heavy haul rails

BackgroundFinite element modeling of human bone provides a powerful tool to evaluate a wide variety of outcomes in a highly repeatable and parametric manner. These models are most often derived from computed tomography data, with mechanical properties related to bone mineral density (BMD) from the x-ray energy attenuation provided from this data. To increase accuracy, many researchers report the use of quantitative computed tomography (QCT), in which a calibration phantom is used during image acquisition to improve the estimation of BMD. Since model accuracy is dependent on the methods used in the calculation of BMD and density-mechanical property relationships, it is important to use relationships developed for the same anatomical location and using the same scanner settings, as these may impact model accuracy. The purpose of this literature review is to report the relationships used in the conversion of QCT equivalent density measures to ash, apparent, and/or tissue densities in recent finite element (FE) studies used in common density-modulus relationships. For studies reporting experimental validation, the validation metrics and results are presented.ResultsOf the studies reviewed, 29% reported the use of a dipotassium phosphate (K2HPO4) phantom, 47% a hydroxyapatite (HA) phantom, 13% did not report phantom type, 7% reported use of both K2HPO4 and HA phantoms, and 4% alternate phantom types. Scanner type and/or settings were omitted or partially reported in 31% of studies. The majority of studies used densitometric and/or density-modulus relationships derived from different anatomical locations scanned in different scanners with different scanner settings. The methods used to derive various densitometric relationships are reported and recommendations are provided toward the standardization of reporting metrics.ConclusionsThis review assessed the current state of QCT-based FE modeling with use of clinical scanners. It was found that previously developed densitometric relationships vary by anatomical location, scanner type and settings. Reporting of all parameters used when referring to previously developed relationships, or in the development of new relationships, may increase the accuracy and repeatability of future FE models.

The novel form of composite walling system consists of two skins of profiled steel sheeting with an in-fill of concrete. The behaviour of such walling under in-plane shear is important in order to utilise this system as shear elements in a steel framed building. Steel sheet-concrete interface governs composite action, overall behaviour and failure modes of such walls. This paper describes the finite element (FE) modelling of the shear behaviour of walls with particular emphasis on the simulation of steel-concrete interface. The modelling of complex non-linear steel-concrete interaction in composite walls is conducted by using different FE models. Four FE models are developed and characterized by their approaches to simulate steel-concrete interface behaviour allowing either full or partial composite action. Non-linear interface or joint elements are introduced between steel and concrete to simulate partial composite action that allows steel-concrete in-plane slip or out of plane separation. The properties of such interface/joint elements are optimised through extensive parametric FE analysis using experimental results to achieve reliable and accurate simulation of actual steel-concrete interaction in a wall. The performance of developed FE models is validated through small-scale model tests. FE models are found to simulate strength, stiffness and strain characteristics reasonably well. The performance of a model with joint elements connecting steel and concrete layers is found better than full composite (without interface or joint elements) and other models with interface elements. The proposed FE model can be used to simulate the shear behaviour of composite walls in practical situation.

Flip-chip electronic package undergoes thermal loading during its curing process and operational life. Due to the thermal expansion coefficient (CTE) mismatch of various components, the flip-chip assembly experiences various types of thermally induced stresses and strains. Experimental measurement of these stresses and strains is extremely tedious and rigorous due to the physical limitations in the dimensions of the flip-chip assembly. While experiments provide accurate assessment of stresses and strains at certain locations, a parallel finite element (FE) analysis and analytical study can complementarily determine the displacement, strain and stress fields over the entire region of the flip-chip assembly. Such combination of experimental, finite element and analytical studies are ideal to yield a successful stress analysis of the flip-chip assembly under the various loading conditions. In this study, a two-dimensional finite element model of the flip-chip consisting of the silicon chip, underfill, solder ball, copper pad, solder mask and substrate has been developed. Various stress components under thermal loading condition ranging from −40°C to 150°C have been determined using both the finite element and analytical methods. Stresses such as (σ11, σ12, ε12 etc. are extracted and analyzed for the individual components as well as the entire assembly, and the weakest positions of the flip-chip have been discovered. Detailed description of FE modeling is presented and the different failure modes of chip assembly are discussed.

After several iterations four rectangular, under-reinforced concrete beams modeled in this study. The specimens were divided into two series of control and strengthened beams, according to the specimen's characteristics. ANSYS finite element program was chosen to perform the analysis. For defining concrete materials, concrete nonlinear material from ANSYS material library was chosen and filled by entering the elastic modulus, compressive strength and Poision's ratio. The steel for the finite element models was grade 60 steel with 200 GPa elastic modulus and assumed to be an elastic-perfectly plastic material. FRP compositesare materials that consist of two constituents; one constituent is the reinforcement, which is embedded in the second constituent, a continuous polymer called the matrix. Therefore the FRP composites are especially orthotropic material.

This paper presents the finite elements of beam-column joints subjected to cyclic loads. This study aims to numerically obtain the beam-column joints' capacity without shear reinforcement in the joints. The variable used in the specimen is the beam's longitudinal reinforcement ratio. While the analytical study was carried out using ATENA 2D software, a computer program based on the non-linear finite element method. In this analytical study, the beam-column joints are loaded cyclically to obtain the envelope curve of the hysterical response. The results of this numerical analysis are then compared with the test results. The comparison results show that the model used in ATENA 2D can approach the test results well. In addition, the crack pattern obtained from the analysis shows a pattern close to the test results.

Investigation of built-up box columns composed of four cold-formed steel channels

Coupled boundary element/finite element analysis in geomechanics including body forces

The proximal humerus is the most common site of occurrence of primary bone tumors in the upper limb. Endoprosthetic replacement is deemed as the preferred reconstructive option following primary resection of bone tumors. However, it has been also associated with complications such as stress shielding and aseptic loosening compromising prosthetic survival. Our objective was to conduct a finite element (FE) study to investigate the effect of varying endoprosthesis length on bone stresses as well as to quantify the extent of stress shielding across the bone length (BL) in a humerus-prosthesis assembly for proximal humeral replacement after tumor excision thereby allowing us to identify the optimal implant length with best biomechanical performance. FE models of the intact humerus and humerus-prosthesis assemblies were established where they were loaded at the elbow joint under torsion with the glenohumeral joint fixed to represent twisting. After dividing the bone into individual slices consisting of 5% BL, the maximum cortical and cancellous principal, von Mises and shear bone stresses were calculated. To measure the level of stress shielding, the percentage stress change from the intact state was evaluated across each slice. Similar stress patterns were observed between the intact state and shorter endoprosthesis compared to the longer endoprostheses. Our findings illustrated the possibility of stress shielding occurring under torsional forces with its effect increasing with implant lengthening. To conclude, we believe that using a shorter prosthesis may substantially diminish the risk of potential implant failure due to stress shielding.

PurposeDorsal screw-rod instrumentations are used for a variety of spinal disorders. Cross-links (CL) can be added to such constructs, however, no clear recommendations exist. This study aims to provide an overview of the available evidence on the effectiveness of CL, potentially allowing to formulate recommendations on their use.MethodsA systematic literature review was performed on PubMed and 37 original articles were included and grouped into mechanical, biomechanical, finite element and clinical studies. The change in range of motion (ROM) was analyzed in mechanical and biomechanical studies, ROM, stiffness and stress distribution were evaluated in finite element studies and clinical outcome parameters were analyzed in clinical studies.ResultsA relative consistent reduction in ROM in axial rotation with CL-augmentation was reported, while minor and less consistent effects were observed in flexion–extension and lateral bending. The use of CLs was clinical beneficial in C1/2 fusion, while the limited clinical studies on other anatomic regions show no significant benefit for CL-augmentation.ConclusionWhile CL provides some additional axial rotation stability in most situations, lateral bending and flexion–extension are less affected. Based on clinical data, CL-augmentation can only be recommended for C1/2 instrumentations, while for other cases, further clinical studies are needed to allow for evidence-based recommendations.

Finite element (FE) study. Pedicle subtraction osteotomy (PSO) is a surgical method to correct sagittal plane deformities. In this study, we aimed to investigate the biomechanical effects of lumbar disc degeneration on the instrumentation following PSO and assess the effects of using interbody spacers adjacent to the PSO level in a long instrumented spinal construct. A spinopelvic model (T10-pelvis) with PSO at the L3 level was used to generate 3 different simplified grades of degenerated lumbar discs (mild (Pfirrmann grade III), moderate (Pfirrmann grade IV), and severe (Pfirrmann grade V)). Instrumentation included eighteen pedicle screws and bilateral primary rods. To investigate the effect of interbody spacers, the model with normal disc height was modified to accommodate 2 interbody spacers adjacent to the PSO level through a lateral approach. For the models, the rods' stress distribution, PSO site force values, and the spine range of motion (ROM) were recorded. The mildly, moderately, and severely degenerated models indicated approximately 10%, 26%, and 40% decrease in flexion/extension motion, respectively. Supplementing the instrumented spinopelvic PSO model using interbody spacers reduced the ROM by 22%, 21%, 4%, and 11% in flexion, extension, lateral bending, and axial rotation, respectively. The FE results illustrated lower von Mises stress on the rods and higher forces at the PSO site at higher degeneration grades and while using the interbody spacers. Larger and less degenerated discs adjacent to the PSO site may warrant consideration for interbody cage instrumentation to decrease the risk of rod fracture and PSO site non-union.