Dynamic mechanical-thermal, microstructural and mechanical analysis of ultra-light polymer-metal composites: influence of forming

A really particular and innovative metal-polymer sandwich material is Hybrix. Hybrix is a product developed and manufactured by Lamera AB, Gothenburg, Sweden. This innovative hybrid material is composed by two relatively thin metal layers if compared to the core thickness. The most used metals are aluminum and stainless steel and are separated by a core of nylon fibres oriented perpendicularly to the metal plates. The core is then completed by adhesive layers applied at the PA66-metal interface that once cured maintain the nylon fibres in position. This special material is very light and formable. Moreover Hybrix, depending on the specific metal which is used, can achieve a good corrosion resistance and it can be cut and punched easily. Hybrix architecture itself provides extremely good bending stiffness, damping properties, insulation capability, etc., which again, of course, change in magnitude depending in the metal alloy which is used, its thickness and core thickness. For these reasons nowadays it shows potential for all the applications which have the above mentioned characteristic as a requirement. Finally Hybrix can be processed with tools used in regular metal sheet industry and can be handled as solid metal sheets. In this master thesis project, pre-formed parts of Hybrix were studied and characterized. Previous work on Hybrix was focused on analyze its market potential and different adhesive to be used in the core. All the tests were carried out on flat unformed specimens. However, in order to have a complete description of this material also the effect of the forming process must be taken into account. Thus the main activities of the present master thesis are the following: Dynamic Mechanical-Thermal Analysis (DMTA) on unformed Hybrix samples of different thickness and on pre-strained Hybrix samples, pure epoxy adhesive samples analysis and finally moisture effects evaluation on Hybrix composite structure.

Analysis of retrieved shoulder prostheses

In the last years the number of shoulder arthroplasties has been increasing. Simultaneously the study of their shape, size and strength and the reasons that bring to a possible early explantation have not yet been examined in detail. The research carried out directly on explants is practically nonexistent, this means a poor understanding of the mechanisms leading the patient and so the surgeon, to their removal. The analysis of the mechanisms which are the cause of instability, dislocation, broken, fracture, etc, may lead to a change in the structure or design of the shoulder prostheses and lengthen the life of the implant in situ. The idea was to analyze 22 explants through three methods in order to find roughness, corrosion and surface wear. In the first method, the humeral heads and/or the glenospheres were examined with the interferometer, a machine that through electromagnetic waves gives information about the roughness of the surfaces under examination. The output of the device was a total profile containing both roughness and information on the waves (representing the spatial waves most characteristic on the surface). The most important value is called "roughness average" and brings the average value of the peaks found in the local defects of the surfaces. It was found that 42% of the prostheses had considerable peak values in the area where the damage was caused by the implant and not only by external events, such as possibly the surgeon's hand. One of the problems of interest in the use of metallic biomaterials is their resistance to corrosion. The clinical significance of the degradation of metal implants has been the purpose of the second method; the interaction between human body and metal components is critical to understand how and why they arrive to corrosion. The percentage of damage in the joints of the prosthetic components has been calculated via high resolution photos and the software ImageJ. The 40% and 50% of the area appeared to have scratches or multiple lines due to mechanical artifacts. The third method of analysis has been made through the use of electron microscopy to quantify the wear surface in polyethylene components. Different joint movements correspond to different mechanisms of damage, which were imprinted in the parts of polyethylene examined. The most affected area was located mainly in the side edges. The results could help the manufacturers to modify the design of the prostheses and thus reduce the number of explants. It could also help surgeons in choosing the model of the prosthesis to be implanted in the patient.