Volume and Distribution of Periprosthetic Bone Cysts in the Distal Tibia and Talus before Early Revision of Total Ankle Arthroplasty

Periprosthetic osteolysis is a common complication following total ankle arthroplasty (TAA). However, understanding of osteolysis volume and distribution is still evolving, undermining efforts to reduce the incidence of osteolysis via bone remodeling. We obtained data on the characteristics of osteolysis developing within the distal tibia and talus after TAA. Three-dimensional computed tomography (3D-CT) reconstructions of 12 patients who underwent HINTEGRA TAA were performed. We identified 27 volumes of interest (VOIs) in the tibia and talus and used statistical methods to identify the characteristics of osteolysis in the VOIs. The osteolysis volume was significantly larger in the talus than in the tibia (162.1 ± 13.6 and 54.9 ± 6.1 mm3, respectively, p = 0.00). The extent of osteolysis within the peri-prosthetic region was greater than within other regions (p < 0.05). Particularly, in the talus, the region around the talar pegs exhibited 24.2 ± 4.5% more osteolysis than any other talar region (p = 0.00). Our results may suggest that extensive osteolysis within the peri-prosthetic region reflects changes in stress flow and distribution, which vary according to the design and placement of the fixation components. This is the first study to report 3D osteolysis patterns after TAA. Careful planning of TAA design improvements may reduce the incidence of osteolysis. Our results will facilitate the further development of TAA systems.

Numerical Modeling of Independent versus Dependent Tensile -Frictional Strength Behavior of Synthetic Rocks with Non-continuous joints

The failure mechanisms of non-continuous jointed rocks under compression loading is of great importance for the rock mechanics community; it plays an important role in understanding the fracturing pattern, the type of the fractures, and the strength of the rock mass under investigation. In this paper, the relationship between the tensile and frictional strength of jointed rock samples is investigated by numerical modeling. Previously tested samples were used to simulate the behavior of artificial jointed rock numerically under axial loading by using two strength criteria; the first assumes that tensile failure reduces shear strength parameters to their residual values (dependent behavior, Model 1) and the second assumes that tensile failure will not cause the shear strength parameters to be reduced to their residual values (independent behavior, Model 2). The numerical model, in this paper uses, Mohr-Coulomb shear strength criterion with parameters of cohesion, friction, and tensile strength cut-off as tested in the laboratory. These artificial rock samples contains open-joints with the same inclination but with different bridge’s inclinations of 45°, 60°, and 75°. These samples were tested in the laboratory under incremental uniaxial loading until failure while monitoring displacement and rupturing development. As the stress concentration increased, curvilinear yielding (wing crack) started near or at the joint tips and propagated and stopped or coalesced to form a continuous rupture surface. The numerical model showed that tensile stress concentration caused wing crack initiation due to stress flow around the pre-existing non-persistent open joints. The yielding behavior of the numerical simulations - under the two tensile strength failure criteria - and the laboratory tests shows good agreement for the three samples. However, when the shear strength and tensile strength parameters are independent, the results showed strong and significant agreement between the laboratory tests and the numerical models in terms of the yielding path, width of failure zone, and the uniaxial strength. In this all compressive load environment, stress flow caused tensile stress concentration near the joint tip and according to the results of this paper the tensile yielding should not force the shear strength parameters to go to their residual values.

Numerical investigation of friction crush welding aluminium and copper sheet metals with flanged edges

Aluminum alloys are the most attractive solutions for many industries including aerospace, marine, and other transportation sectors where lightweight construction is required. Friction Crush Welding (FCW) is a new material joining process that simultaneously creates a mechanical lock and a metallurgical seal at the interface between similar and dissimilar materials. In this research work presents the development of numerical modelling to predict the temperature distribution and mechanical performance of aluminum and copper similar joints in the FCW of sheet metal section. An explicit nonlinear transient finite element thermomechanical model is develop using ABAQUS based on the coupled Euler-Lagrange method to simulate FCW of AW5754 and Cu-DHP alloys. The Johnson-Cook materials law is adopted in the FEM. Numerical investigations of the FCW process was performed to reduce experimental testing times, which can be long and expensive. Temperature distribution and von misses stress flow patterns are observed at the top surface of the weld. Numerical simulation data correlate with experimental data in the literature.

Proposition and analysis of strut and tie models for short corbels from techniques of topology optimization

Reinforced concrete short corbels are components characterized to represent typical conditions of geometrical and static discontinuity. In general, the classical bending theory is not valid for their design. With the strut and tie method, a model of a self-balanced truss, a strategy of representation of the principal stress flow appears as a representation of the trajectories of the main stresses in these components. Within the context of obtaining the strut and tie models, topology optimization is an indicated technique for an automated process. Combined with a numerical analysis based on finite elements, the SIMP (Solid Isotropic Material with Penalization) method formulation, which is defined with the criterion of minimum strain energy restricted by the volumetric fraction, is used for the development of the models with the ABAQUS® v. 6.14.1 software. Therefore, with the material distribution posterior to the optimization and the validation based on normative codes, it is demonstrated that the tool is effective in the development of strut and tie models.

Helmet chinstrap protective role in maxillofacial blast injury

BACKGROUND: The protective role of helmet accessories in moderating stress load generated by explosion shock waves of explosive devices is usually neglected. OBJECTIVE: In the presented study, the protective role of the helmet chinstrap against the impulse and overpressure experienced by the maxillofacial region were examined. METHODS: The explosion shock wave and skull interaction were investigated under three different configurations: (1) unprotected skull, (2) skull with helmet (3) skull with helmet and chinstrap. For this purpose, a 3D finite element model (FEM) was constructed to mimic the investigated biomechanics module. Three working conditions were set according to different explosive charges and distances to represent different load conditions. Case 1: 500 mg explosive trinitrotoluene (TNT), 3 cm, case 2: 1000 mg TNT, 3 cm, and case 3: 1000 mg TNT and 6 cm distance to the studied object. The explosion effect was discussed by examining the shock wave stress flow pattern. Three points were selected on the skull and the stress curve of each point position were illustrated for each case study. RESULTS: The results showed that the helmet chinstrap can reduce the explosive injuries and plays a protective role in the maxillofacial region, especially for the mandible.