Krystyna Imielińska

Effect of Adhesive Compliance in the Assessment of Soft Adhesives with the Wedge Test

Wedge tests are usually analysed assuming that the free, unbonded members may be treated as encastré cantilever beams. However, if the adhesive layer is sufficiently flexible (e. g., due to low elastic modulus), then significant strain in the bonded region may occur and lead to modification of the behaviour outside this region. Using in conjunction a sensitive strain gauge method on asymmetric wedge tests and a mathematical analysis developed from the work of Winkler, we conclude that the standard, simple beam theory approach significantly overestimates crack length for a supple adhesive layer. The present contribution mainly considers strain effects in the intact, bonded zone, rather than fracture per se. However, it is concluded that, if in fracture tests, the incorrect values of crack length obtained from the encastré beam assumption are employed to calculate fracture energy using the simpler model, there will be some self-compensation and little error in estimates of the latter will result (at least in the cases presently studied).

Fracture in Composite/Aluminium Joints of Variable Adhesive Properties

A strain gauge technique recently developed with the wedge test, for estimating crack length and, thus, the fracture energy of structural adhesive bonding, has been employed on a system in which one adherend had two types of surface treatment. Simple polishing and polishing with subsequent sandblasting were the treatments used, with a distinct straight line, perpendicular to the sample edges, separating the two. Despite the clear-cut difference in surface treatment, smooth transitions in crack growth speed were noted. This can be explained by the existence of a curved crack front, encroaching gradually on one surface-treated zone, whilst remaining partially on the other. Crack length, a, vs. time, t, curves were exploited to obtain fracture energy vs. crack speed. The multi-valued nature of the relation can also be explained by a non-rectilinear fracture front. The method is proposed as a method for reproducible comparison of surface treatments.

Water sorption and blistering of GFRP laminates with varying structures

Abstract The microstructures, water absorption as well as blistering was studied for bi- and tri- axial glass fibre vinyl ester and polyester -matrix laminates coated with gel coat layer and uncoated. The effect of manufacturing technique on water sorption characteristics was considered. It was found that water sorption characteristics of GFRP depend on manufacturing methods. The least water intake was found for specimens having perfect microstructure due to manufacturing by infusion process. Water sorption saturation value was reached after ca. 50 days of accelerated test at 70°C and was found to correspond to 250 days conditioning at 20°C. Blistering evolution was illustrated and SEM images shown corresponding to degradation of the gel coat layer and the laminate during the exposure in water.

ON DEGRADATION OF GLASS/POLYESTER LAMINATE IMMERSED IN WATER

ON DEGRADATION OF GLASS/POLYESTER LAMINATE IMMERSED IN WATER Mechanical behaviour was compared for glass/polyester laminates manufactured in the boatbuilding plant using three methods: hand lay-up, vacuum bagging, infusion. Specimens were tested in dry condition and following accelerated water immersion test (70°C- corresponding to the exposure of 30 years at 19°C). In three point bending test 40-50% reduction in laminate strength was observed due to water immersion. The highest degradation was in samples manufactured using hand lay-up method, the differences in strength between both vacuum methods were insignificant. Interlaminar shear strength was reduced by 25% for infusion method which is recommended as the most efficient. Matrix plasticization and debondings as well as surface microcracks were responsible for reduction in strength for water conditioned specimens. However, no microstructural difference in type or intensity of internal damage was observed for the three sample types.

Impact Behaviour of Glass Fribre /Epoxy Composites with Nano-Enhanced Resin after Water Exposure

Abstract Impact behaviour of glass fibre /epoxy composites with nano- SiO2 modified resin was studied in terms of low velocity impact after water exposure. Nanocomposites with 1%, 2%, 3% 5% 7% nano-SiO2 (Nanopox- Evonic) were investigated. Peak impact load and impact damage area as a function of nanoparticle contents were compared for dry specimens and for samples exposed to water (0.7 %wt. 1.7% water absorbed) at 1J, 2J 3J impact energies. For unmodified composite peak force was higher than for 3% modified specimens and higher for dry specimens than those exposed to water. Impact damage areas were plotted as a function of water contents for modified and unmodified samples. Failure modes were illustrated using SEM micrographs. Numeropus matrix cracks were the dominating failure mode in dry speciemens both unmodified and the modified. Fibre fracture was observed at 3J impact energy in all dry unmodified samples, however water exposure prevented early fibre fracture in nanocomposites. The proposed energy absorption mechanism is nanoparticles debonding.

Effect of SiO2 Nanoparticles on the Mechanical and Low Velocity Impact Properties of Epoxy/Glass Composites

Flexural strength and low velocity impact properties were investigated in terms of possibile improvements due to epoxy matrix modification by SiO2 nanoparticles (1%, 2%, 3%, 5%, 7%wt.) in glass/epoxy laminates formed using hand lay-up method. The matrix resin was Hexion L285 (DGEBA) with Nanopox A410 - SiO2 (20 nm) nanoparticle suspension in the base epoxy resin (DGEBA) supplied by Evonic. Modification of epoxy matrix by variable concentrations of nanoSiO2 does not offer significant improvements in the flexural strength σg, Young’s modulus E and interlaminar shear strength for 1% 3% and 5% nanoSiO2 and for 7% a slight drop (up to ca. 15-20%) was found. Low energy (1J) impact resistance of nanocomposites represented by peak load in dynamic impact characteristics was not changed for nanocompoosites compared to the unmodified material. However at higher impact energy (3J) nanoparticles appear to slightly improve the impact energy absorption for 3% and 5%. The absence or minor improvements in the mechanical behaviour of nanocomposites is due to the failure mechanisms associated with hand layup fabrication technique: (i.e. rapid crack propagation across the extensive resin pockets and numerous pores and voids) which dominate the nanoparticle-dependent crack energy absorption mechanisms (microvoids formation and deformation).

Analysis and Comparison of Safety of Children and Adult Passenger in Car Based on Crash Tests Results

Most important features of the child seat were presented. There was made analysis of selected dynamic loads acting on mannequins heads during a collision. Comparison of loads acting on the kid in a child seat and the other passengers in a car is presented. In analysis of the results particular attention has been paid on the childrens secure in a car. The phenomena of collision childs occipital bone with seat backrest was described. There were presented results of dynamic test of chosen kind of materials, which were expected for having good energy absorbing characteristic. Selected courses of dynamic forces, values of peak forces and time of dynamic forces acting for tested materials were shown. The tests were made on dynamic droptower impact system Instron CEAST 9310.

Degradation of GFRP Marine Laminates with Nano Particle Modified Coatings

Abstract Water absorption and surface blistering behaviour was studied for polyester-matrix laminates with SiO2 nanoparticle reinforced gel coats. Accelerated water immersion tests at 37°C showed that addition of 10% nanoparticles increases blisters incubation time by ca. 50% compared to 5% and 0% nanoparticles composites.

DYNAMIC MECHANICAL BEHAVIOUR OF GFRP COMPOSITES WITH SiO2 NANO PARTICLES REINFORCED EPOXY MATRIX

ABSTRACT Dynamic mechanic (DMA) tests were performed to compare the mechanical behaviour of glass fibre reinforced epoxy laminate composites with SiO2 nanoparticle reinforced matrix. The selection of the most promising nanoparticle concentrations was considered in terms of elastic modulus and glass transition temperature. The reference specimens (0% nanoparticles) did not contain diluent accordingly the results do not allow the exact comparison with unreinforced composite, nevertheless the ranking of the nanocomposites was made. In terms of stiffness requirements 20% nanoparticles composites offer the best behaviour, 25% higher elastic modulus than 5% nanoparticles. For nano composites the glass transition temperature TG is the highest: 80°C, 77°C for 3%, 5% nanoparticles respectively and the lowest 75°C, 72°C , 71°C for 15%, 10% and 20% nanoparticles is respectively .

Degradation of Gel-Coat Layer in Glass/Polyester Laminate in Seawater Environment

Glass/polyester laminate coated with gelcoat layer of different thickness 0,5; 1,5; 3 mm was studied in terms of blistering behaviour and water sorption in hot water environment. Blistering was found to be accelerated for thin (0,5 mm) gel-coat layer compared to the thick (1,5; 3 mm), however no significant difference in blistering behaviour was observed between the laminates with gel-coat thickness 1,5 and 3 mm which may suggest that increasing the gel-coat thickness is effective only to a certain thickness limit. Microscopic studies demonstrated that blistering behaviour was related to the formation of subsurface cracks – longer and less densely distributed in thin gel-coat layers in contrast to numerous small cracks formed in the thick gel-coats.