Mechanical properties evaluation for engineering materials utilizing instrumented indentation: Finite element modelling approach

Instrumented indentation technique gives the possibility to determine the mechanical properties for small specimens and material in service. Several researchers have attempted to evaluate this approach experimentally and investigated the factors that affect it by using different indenter’s geometries for different engineering materials. In this work, the instrumented indentation technique was used to evaluate the mechanical properties experimentally and numerically using finite element simulation to understand the contact mechanics between the indenter surface and the substrate for two types of steel alloys namely ASTM516-G70 and AISI1010 steel. Two shapes of indenters, blunt (spherical) and sharp (Vickers) were used. The results were then compared with the experimental results extracted from the instrumented indentation test. The results have demonstrated a good agreement between the experimental and the finite element simulation results with error bound a ±5 % for young’s modulus and ±7.7 % for yield strength. Whereas excellent agreement is observed in the elastic region and the beginning of the plastic region for the true stress-strain curve. Finally, it is to be emphasized that the obtained results are more applicable for the tested materials and further research is recommended to accommodate other materials as well and to confirm the generality of this method.

Modified MCL Indentation Technique in Total Knee Arthroplasty With Severe Type II Valgus Deformity

Purpose A modified technique, medial indentation of the medial collateral ligament(MCL),was usedin total kneearthroplastywith severe type II valgus deformity. The study compared the clinical outcomes of the technique relative to conventional release group. Methods Consecutive patients with a Krackow type II valgus deformity of >20° who underwent a primary unilateral TKA between May 2008 and June 2017 were retrospectively studied. Modified MCL indentation technique was performed in 20 patients (group A), while the remaining 23 patients (group B) received routine release technique. Radiological parameters, such as the valgus angle (VA), and functional outcomes including the use of constraint implants, Knee Society Score(KSS), Knee Society function score(KSF), and height of the polyethylene insert, were compared between the two groups.Results 43 consecutive patients had a minimum 2-year follow-up. The preoperative VA was comparable between group A (23.5° ± 5.8°) and group B (21.3° ± 3.2°, P =0.134), so was the postoperative VA (1.1° ± 2.1° and 2.5° ± 3.0°, P =0.084 in groups A and B, respectively).The postoperative KSS and KSF showed marked improvement. While no statistically significant difference in preoperative or postoperative functional scores was found between two groups, group A had thinner PE insert (9.5 ± 1.1 mm vs. 12.9 ± 1.5 mm) and less use of constrained condylar inserts(15% vs. 69.6%). Conclusion Modified MCL indentation technique can achieve good outcomes in TKA with type II valgus deformity of >20°.