Charles Simoneau

Adaptive Composite Panel with Embedded SMA Actuators: Modeling and Validation

This article focuses on the development of a finite elements model of an adaptive composite panel with embedded shape memory alloy actuators. It is firstly shown that a combination of shell, beam and link elements could be employed to model the panel. A simplified version of the Likhachev model is then employed as the constitutive relation for the actuators. Several experimental tests were successfully carried out on a prototype to validate the model and to demonstrate the possibility of controlling the panel shape. Further works should consider improving the technique employed for reading the actuators’ temperature during experimental tests.

Femoral stem incorporating a diamond cubic lattice structure: Design, manufacture and testing

BACKGROUND The current total hip prostheses with dense femoral stems are considerably stiffer than the host bones, which leads to such long-term complications as aseptic loosening, and eventually, the need for a revision. Consequently, the lifetime of the implantation does not match the lifetime expectation of young patients. METHOD A femoral stem design featuring a porous structure is proposed to lower its stiffness and allow bone tissue ingrowth. The porous structure is based on a diamond cubic lattice in which the pore size and the strut thickness are selected to meet the biomechanical requirements of the strength and the bone ingrowth. A porous stem and its fully dense counterpart are produced by laser powder-bed fusion using Ti-6Al-4V alloy. To evaluate the stiffness reduction, static testing based on the ISO standard 7206-4 is performed. The experimental results recorded by digital image correlation are analyzed and compared to the numerical model. RESULTS & CONCLUSIONS The numerical and experimental force-displacement characteristics of the porous stem show a 31% lower stiffness as compared to that of its dense counterpart. Moreover, the correlation analysis of the total displacement and equivalent strain fields allows the preliminary validation of the numerical model of the porous stem. Finally, the analysis of the surface-to-volume and the strength-to-stiffness ratios of diamond lattice structures allow the assessment of their potential as biomimetic constructs for load-bearing orthopaedic implants.

Design, manufacturing, and testing of an adaptive composite panel with embedded shape memory alloy actuators

This article presents a novel design procedure leading to fabrication of a composite adaptive panel prototype with an embedded array of linear shape memory alloy actuators. This procedure allows determination of the panel’s radius of curvature as a function of the shape memory alloy actuators’ actuation temperature and panel configuration (number and orientation of plies, number and location of actuators, the materials’ properties, and the geometric arrangement). This design procedure integrates properties of the host structure (composite laminate) and of the actuators (shape memory alloy wires) in the framework of a unique design diagram. The performances of shape memory alloy actuators are obtained by experimental manipulations, whereas the rigidity of the host structure is calculated using the finite element numerical modeling approach. To validate the developed design procedure, a [90/90/90/wire/90] 425 × 425 × 5-mm adaptive panel prototype is fabricated using the vacuum-assisted resin transfer molding method. The results obtained from experimental tests are used to monitor the global performance of the adaptive panel and to validate the developed design procedure.

Development and in vitro validation of a simplified numerical model for the design of a biomimetic femoral stem

BACKGROUND Dense and stiff metallic femoral stems implanted into femurs for total hip arthroplasties produce a stress shielding effect since they modify the original load sharing path in the bony structure. Consequently, in the long term, the strain adaptive nature of bones leads to bone resorption, implant loosening, and the need for arthroplasty revision. The design of new cementless femoral stems integrating open porous structures can reduce the global stiffness of the stems, allowing them a better match with that of bones and provide their firm fixation via bone ingrowth, and, thus reduce the risk of implantation failure. METHODS This paper aims to develop and validate a simplified numerical model of stress shielding, which calculates the levels of bone resorption or formation by comparing strain distributions on the surface of the intact and the implanted femurs subjected to a simulated biological loading. Two femoral stems produced by laser powder-bed fusion using Ti-6Al-4V alloy are employed: the first is fully dense, while the second features a diamond cubic lattice structure in its core. The validation consists of a comparison of the numerically calculated force-displacement diagrams, and displacement and strain fields with their experimental equivalents obtained using the digital image correlation technique. RESULTS AND CONCLUSIONS The numerical models showed reasonable agreement between the force-displacement diagrams. Also, satisfactory results for the correlation analyses of the total displacement and equivalent strain fields were obtained. The stress shielding effect of the implant was assessed by comparing the equivalent strain fields of the implanted and intact femurs. The results obtained predicted less bone resorption in the femur implanted with the porous stem than with its dense counterpart.

Development of a Biomimetic Metallic Femoral Stem: Methodological Approach

In this communication, a new methodological approach is proposed to develop a biomimetic metallic femoral stem. The design of this stem starts with the definition of an outer skin by reproducing the shape and overall dimensions of a Stryker® femoral stem to be implanted in an artificial femur model from Sawbones®. In-house algorithms are then used to generate two types of porous structures inside the outer skin: either a stochastic cubic-based porous structure or an ordered diamond-type porous structure. Next, a model of the femur-stem assembly is developed using the finite element method. The fully dense Stryker stem replica and two porous stems are fabricated using selective laser melting technology. Then, comparative mechanical testing is carried out using the ISO 7206-4 (2010) guidelines. These tests are conducted on an intact artificial femur (reference case) and on the identical femurs, but now implanted with the fully dense and porous stems. Using digital image correlation tools, the results of four series of tests are compared to assess which implant design leads to the lowest stress shielding in the implanted femur. Finally, the experimentally measured strain fields are compared to the numerical predictions to validate the numerical models.