The in vivo location of edge-wear in hip arthroplasties

Aims Acetabular edge-loading was a cause of increased wear rates in metal-on-metal hip arthroplasties, ultimately contributing to their failure. Although such wear patterns have been regularly reported in retrieval analyses, this study aimed to determine their in vivo location and investigate their relationship with acetabular component positioning. Methods 3D CT imaging was combined with a recently validated method of mapping bearing surface wear in retrieved hip implants. The asymmetrical stabilizing fins of Birmingham hip replacements (BHRs) allowed the co-registration of their acetabular wear maps and their computational models, segmented from CT scans. The in vivo location of edge-wear was measured within a standardized coordinate system, defined using the anterior pelvic plane. Results Edge-wear was found predominantly along the superior acetabular edge in all cases, while its median location was 8° (interquartile range (IQR) -59° to 25°) within the anterosuperior quadrant. The deepest point of these scars had a median location of 16° (IQR -58° to 26°), which was statistically comparable to their centres (p = 0.496). Edge-wear was in closer proximity to the superior apex of the cups with greater angles of acetabular inclination, while a greater degree of anteversion influenced a more anteriorly centred scar. Conclusion The anterosuperior location of edge-wear was comparable to the degradation patterns observed in acetabular cartilage, supporting previous findings that hip joint forces are directed anteriorly during a greater portion of walking gait. The further application of this novel method could improve the current definition of optimal and safe acetabular component positioning. Cite this article: Bone Joint Res 2021;10(10):639–649.

Mapping of Wear Mechanism for Mechanical Alloyed Aluminum Carbon Nanotube Composites—An In Situ Analysis

This research work investigates the root causes of wear on the tribo surface of mechanically alloyed Aluminum/CNT composite through a simulated in situ analysis. The wear maps are developed using the second-order polynomial regression equation for the Aluminum/CNT composite to discriminate the wear mechanisms at different levels of their influencing factors and milling parameters. As a result, the predominant wear mechanism is identified as surface fatigue for Aluminum/CNT composite under high loading dry sliding condition. This study also reveals the modes for eliminating the severe wear at the tribo-surfaces. Aluminum/CNT1 wt% composite fabricated with the mechanical alloying parameters above 6 h of milling time and above 5 rps of milling speed eliminates the delamination under low level of tribological parameters, and it achieves the minimal wear-rate of 30.5 × 10−6 g/m and coefficient of friction (CoF) of 0.346.

Experimental Investigation and Simulation of Aircraft Tire Wear

ABSTRACT Not only in the automotive sector, but also in the field of aircraft tires, the topic of abrasion is of great importance. The aircraft tire manufacturers provide criteria for the permissible degree of wear. If these limits are exceeded, the tire must be replaced or retreaded. By this time, the tire should withstand as many takeoff and landing cycles as possible. Abrasion models should help to predict the wear behavior in preflight modeling. At the Institute of Dynamics and Vibration Research, quasi-steady abrasion tests are performed using tread block samples from an aircraft tire. For various pressures and sliding speeds, the abrasion is determined by recording the mass loss of the rubber sample. Based on these measurement data, a wear model is derived as a function of coefficient of friction, contact pressure, and sliding speed for different ambient temperatures. The well-known brush model forms the basis for the wear simulations. With parameters validated on the aircraft tire, such as contact length, stiffness, and friction coefficient, the resulting mechanical forces within the contact area are calculated. Finally, the classic brush model is extended by the abrasion calculation. The tire wear is determined during unsteady load and slip conditions by use of the quasi-steady wear maps derived from our experiments. Within a measurement campaign on the complete tire, the tread depth is measured after various driving maneuvers and is in good agreement with the simulation results.

Effect of Heat Treatment on Tribological Properties of Ni-B Coatings on Low Carbon Steel: Wear Maps and Wear Mechanisms

Among the alternatives for using low-carbon steel in parts with heavy wear, as gears and bearing surfaces, Ni-B electroless coatings deposited on these steels are considered due to their wear resistance. Wear maps, elaborated from friction or wear results found for different evaluated conditions, are a very useful tool for the selection of materials based on tribological properties. However, wear maps for electroless Ni-B coatings are very scarce. In this work, dry sliding wear tests with different loads and sliding velocities were performed on Ni-B electroless coatings applied on AISI/SAE 1018 steel, with and without heat treatment at 450 °C for 1 h, with the aim of determining the effect of the heat treatment on the friction coefficients and wear rates. Contour and profile maps, and finally friction and wear maps, were constructed for each of the coatings evaluated. The coating properties before and after the heat treatment were studied by means of scanning electron microscopy (SEM), atomic force microscopy (AFM), X-ray diffraction (XRD), scratch tests, nanoindentation, and differential scanning calorimetry (DSC). Sliding wear tracks were studied using SEM, energy-dispersive spectroscopy (EDS), and micro-Raman spectroscopy. Good agreement between experimental and predicted values was found in friction and wear maps. Wear mechanisms change from flattening in less severe conditions to abrasion in more severe conditions, besides spalling and adhesive wear in untreated coatings. Moreover, abrasive wear is lower in heat-treated coating than in untreated coating.