Carbon fibre reinforced polymer (CFRP) composites have found a wide range of applications in the aerospace, marine, sports and automotive industries owing to their lightweight and acceptable mechanical properties compared to the commonly used metallic materials. The currently dominating method of machining CFRP is by mechanical means that has found many problems including extensive tool wear, fibre pull-out and delamination. Lasers as non-contact tools have been widely applied for cutting and drilling materials. However, machining of CFRP composites using lasers can be challenging due to inhomogeneity in the material properties and structures, which can lead to thermal damage such as charring, heat affected zones (HAZs), resin recession and delamination. In previous studies, Nd:YAG, diode pumped solid state (DPSS), CO2 (continuous wave), disk and fibre lasers were used in machining CFRP composites and the control of damage such as the size of heat affected zones (HAZ) and achieving comparable material removal rate with the mechanical processes remain a challenge. Most reported work showed a typical heat affected zone of 0.2-1.2 mm. The availability of short pulsed transversely excited atmospheric (TEA) CO2 lasers and ultra-short laser pulse sources such as picosecond lasers make it possible to improve the laser machining quality of CFRP materials. In this research, the machining of CFRP composites using a microsecond pulsed TEA CO2 laser, a state of the art high power picosecond laser and a 1 kW single mode fibre laser system was investigated. The yielded heat affected zone was less than < 25 µm for the TEA CO2 and the picosecond laser machining, although the material removal rate was low. Additionally, it has been shown that the pulsed fibre laser improved the machining quality compared to that with the continuous mode. A potential application of the fibre laser for composite repair and remanufacturing was investigated. The interactions between picosecond laser beam and CFRP composite were studied in more detail including understanding the self-limiting effect in single and multiple parallel tracks drilling/machining through both experimental and theoretical studies. Furthermore, a sequential laser and mechanical drilling of CFRP was investigated to improve the machining rate. The work performed in this PhD was driven by aerospace industry needs, with the collaboration of Rolls-Royce plc and BAE Systems as industrial partners.

in english Introduction: Composite restorations in the oral cavity are exposed to an aggressive environment and mechanical challenge that gradually impairs their physical and mechanical properties. This may result in an enhanced wear rate, loss of esthetic properties and an increased risk of a restoration fracture or its marginal failure with a negative impact on the restoration's durability. Worn or failed restorations are usually completely replaced, which increases the irreversible loss of dental hard tissues. Repair of composite restorations by their partial replacement is therefore a minimally invasive, preventive and less time-consuming alternative to their complete replacement and increases their longevity. In the oral cavity, the adhesive bond between the existing composite restoration and the repair composite resin is exposed to various chemical substances and mechanical stress, e.g. surfactants in toothpastes, which can initiate its degradation. By decreasing the surface tension, the penetration of water into the adhesive joint can be enhanced, accelerating the hydrolysis of the adhesive and reducing the composite repair strength. The major and not yet fully resolved issue of composite repairs is how to achieve a strong and durable bond between the existing and repair composite materials....

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Indiana University-Purdue University Indianapolis (IUPUI) / Repair is an alternative treatment option in many cases to replacement of resin matrix composite restoration. However, aged resin matrix composites have a limited number of carbon-carbon double bonds to adhere to a new layer of rein. Therefore, surface treatments of the aged resin matrix composite surface prior to repairing could improve the repair bond strength. The objectives of this study were to: 1) To evaluate various surface treatments on shear bond strength of repair between aged and new microhybrid resin matrix composite, and 2) To assess the influence of applying a silane coupling agent after surface treatments. Eighty disk-shaped resin matrix composite specimens were fabricated and thermocycled 5000 times prior to surface treatment. Specimens were randomly assigned to one of the three surface treatments (n = 20): 1) Airborne abrasion with 50 μm aluminum oxide, 2) Tribochemical silica coating (CoJet), or 3) Er,Cr:YSGG laser and control group (n = 20). Specimens were cleaned with 35-percent phosphoric acid, rinsed, and dried. Each group was assigned into two subgroups (n =10): a) no silanization, and b) with silanization. Adhesive agent was applied and new resin matrix composite was bonded to each conditioned surface. Bond strength was evaluated by shear test. Data were analyzed with a two-way ANOVA model. The interaction between conditioning and silanization was significant(p = 0.0163), indicating that comparisons of silanization must be evaluated for each conditioning method, and that comparisons of conditioning methods must be evaluated separately with and without silanization. Airborne particle abrasion showed significantly higher repair bond strength than Er,Cr:YSGG laser without silanization (p < 0.0001) and with silanization(p = 0.0002), and higher repair bond strength than the control without silanization (p < 0.00001) and with silanization (p < 0.00001). Airborne particle abrasion did not have significantly different in repair bond strength than Tribosilica coating without silanization (p = 0.70) or with silanization (p = 0.33). Tribosilica coating had significantly higher repair bond strength than Er,CR:YSGG laser without silanization (p < 0.0001) and with silanization (p < 0.0001), and significantly higher repair bond strength than control without silanization (p < 0.0001), but not with silanization (p =0.16). Er,CR:YSGG laser and control did not have significantly different repair bond strength without silanization (p = 1.00) or with silanization (p = 0.11). There was no effect of silanization on repair bond strength overall (p = 0.34) for any of the surface conditioning methods (p = 0.76 for airborne particle abrasion; p = 0.39 for tribosilica coating; p = 1.00 for Er,Cr:YSGG laser, or p = 0.39 for control). Airborne particle abrasion with 50-μm aluminum oxide particle and tribochemical silica coating followed by the application of bonding agent provided the highest shear bond strength values, suggesting that they might be adequate methods to improve the quality of the repairs of resin-matrix composites.