S. Tsantzalis

Viscoelastic properties of cartilage-subchondral bone complex in osteoarthritis.

Objective: This study examines viscoelastic properties of the ‘unaffected’ tibial condyle in unicompartmental osteoarthritic knees, in order to determine whether to preserve it or not in knee replacement operations. Design: The viscoelastic properties of longitudinal strips of cartilage and subchondral bone from osteoarthritic and healthy knees were studied. Methods: Nine medial compartment osteoarthritic and nine cadaveric knees, all age- and gender-matched, were studied. Samples from polyethylene and methacrylate cement were also obtained and all then tested in the DMA (Dynamic Mechanical Analysis) testing apparatus. The dynamic modulus of elasticity (Edyn) and the loss factor (tan δ) were measured. Results: The medial compartment in osteoarthritic knees had lost its viscoelastic properties, having a significantly higher Edyn compared to the lateral one, and lower values of loss factor. In healthy knees there was no significant difference (p = 0.18) in viscoelastic properties between both compartments and with the unaffected side of the osteoarthritic knee. Polyethylene and cement appear to have a high modulus of elasticity compared to both the healthy and the osteoarthritic knees. Conclusions: The ‘unaffected’ (lateral) tibial condyles in medial compartment osteoarthritic knees seem to preserve their viscoelastic properties; it is worth considering a hemiarthroplasty. The significant modulus of elasticity difference between the condyles-polyethylene-cement results in different deformation in the interface between them and induces micromotion and loosening.

Damage Detection during Fatigue Loading of CNF Doped CFRPs via Resistance Measurements and AE

Vapor growth carbon nanofibers (CNFs) were used as dopants for the epoxy resin (EP) matrix of unidirectional carbon fiber reinforced plastics (CFRPs). The doped laminates were compared to the reference one (with neat EP as matrix) with regard to their fracture toughness, and mechanical quasi-static and fatigue behaviour. Electrical resistance monitoring of the samples was used as a tool for sensing the damage propagation during the various loading configurations. Correlation between these results and acoustic emission (AE) data was also attempted.

Influence of Carbon Nanofibers and Piezoelectric Particles on the Thermomechanical Behaviour of Epoxy Mixtures

Vapor growth carbon nanofibers (CNFs), lead zirconate titanate piezoelectric (PZT) particles, as well as a combination of these two were added in an epoxy resin (EP), and their influence on the curing reaction was investigated. Moreover, the cured samples were characterised by dynamic scanning calorimetry and dynamic thermal mechanical analysis. The presence of the fillers had no significant effect of the curing reaction of the EP system and the glass transition temperature, Tg.

Improved Sensing Properties of Epoxy Resin Polymers and Carbon Fiber Reinforced Epoxy Resin Composites by the Introduction of Multi-Wall Carbon Nanotubes (MWCNT)

The proposed paper will present the manufacturing process of epoxy resin compounds with several multi-wall carbon nanotube (MWCNT) contents per weight and, carbon fibre reinforced polymers with the previous nano-doped epoxy matrix material. Enhanced mechanical properties of the doped specimens both epoxy and carbon reinforced against the neat epoxy testpieces e.g. tensile strength and modulus of elasticity was achieved and attributed to the high surface area and high aspect ratio of the nanotubes. Moreover the dynamic properties of the nano-doped epoxy polymers were investigated and the relation of glass transition temperature with increasing CNT content was found to be inverse. Another goal of the present work was to use the electrical/sensing properties of MWCNTs as a nano- sensor for the damage detection within the matrix material of the CFRPS. Therefore loading-unloading tensile tests were performed, along with on-line conductivity monitoring

Enhancement of the Mechanical Performance of Carbon Fiber Reinforced Epoxy Resin Composites by the Introduction of Carbon Nano-Fibers (CNF)

The proposed paper will present the manufacturing process of CFRP panels with doped epoxy matrix with CNF 1% vol. and their enhanced mechanical properties against the neat. Also a correlation between electrical conductivity and degradation of fatigue properties will be presented. Tensile tests were performed in order to investigate any improvements in the Youngs Modulus. The CNF panel even though had lower Vf, it exhibited greater modulus of elasticity. The next step involved fracture tests in Mode I and Mode II using DCB specimens. It is observed that the toughness increases remarkably after the addition of the CNFs in the matrix of the laminates (100% and 40% increase for Mode I and Mode II, respectively).

Toughening and healing of continuous fibre reinforced composites with bis-maleimide based pre-pregs

Unidirectional (UD) pre-pregs containing self-healing materials based on Diels–Alder reaction bis-maleimide (BMI) polymers were successfully incorporated on the mid-plane of UD carbon fibre reinforced polymers. The fracture toughness of these composites and the introduced healing capability were measured under mode I loading. The interlaminar fracture toughness was enhanced considerably, since the maximum load (P max) of the modified composite increased approximately 1.5 times and the mode I fracture energy (G IC) displayed a significant increase of almost 3.5 times when compared to the reference composites. Furthermore the modified composites displayed a healing efficiency (HE) value of about 30% for P max and 20% for G IC after the first healing, appearing to be an almost stable behaviour after the third healing cycle. The HE displayed a decrease of 20% and 15% for P max and G IC values, respectively, after the fifth healing cycle. During the tests, the monitored acoustic emission (AE) activity of the samples showed that there is no significant difference due to the presence of BMI polymer in terms of AE hits. Moreover, optical microscopy not only showed that the epoxy matrix at the interface is partly infiltrated by the BMI polymer, but it also revealed the presence of pulled out fibres at the fractured surface, indicating ductile behaviour.

Effect of CNT modified matrix of epoxy CFRPs on hydrothermal behaviour of material. Evaluation of water uptake using electrical resistance measurements

Abstract In the present work, reference and nano-modified unidirectional and quasi-isotropic, epoxy matrix, carbon fibre reinforced polymers, were exposed to distilled water at hydrothermal environment. Water uptake was investigated as a function of the CNT matrix wt-% content up to saturation level. In parallel the variation of glass transition temperature Tg was also monitored using DMA tests. The distilled water absorption process was modelled following the Fick’s law, and the experimental results found to be in very good agreement to the theoretical predictions up to saturation. During the tests, at defined time intervals, the variation of the electrical conductivity of the investigated materials was studied and a correlation between the water absorption and the variation of the electrical conductivity was established. Finally, all the reference materials and the ones concluded at the saturation stage were exposed to broadband dielectric measurements at frequency range of 0·1 Hz to 1 MHz.