C. Capela

Fracture assessment of PMMA/Si kitchen sinks made from acrylic casting dispersion

Abstract Acrylic casting dispersion is used to fabricate kitchen sinks made of PMMA/Si which stands for poly-methyl methacrylate mixed with a fine dispersion of silica. The composite is suited for sanitary wares that are subjected to severe temperatures, giving rise to high thermal stresses. This leads to failure by cracking in the region near the drain hole. Such conditions are investigated by determining the mechanical and fracture properties for two different chemical compositions of PMMA. They are referred to by trade marks from ICI as Asterite and Amatis. Data are obtained for temperatures from 0 to 95 °. Extensometry data are also obtained to the thermal stresses around the drain hole subjected to alternating flow of cold and hot water. Critical crack lengths are determined from the critical stress intensity factor and maximum local tensile stresses based on measured data. They are estimated to be 1.5 mm and 4.0 mm, respectively, for the Asterite and Amatis composites. These results confirm with practice where the cracking of the former was observed while the latter did not crack.

Fatigue life predictions in polymer particle composites

Abstract This paper presents a study on fatigue life predictions in three polymer particle composites with different volume fractions of filler and different particle sizes. Central hole notched specimens were analysed using a fracture mechanics approach. A solution for the stress intensity factor of corner cracks at a hole was obtained using the finite element method and considering quarter-circular and quarter-elliptical cracks of different sizes. The solution was compared with a literature solution and significant differences were found. Fatigue crack propagation tests were performed at room temperature and constant loading amplitude, for stress ratios R=0 and R=−0.75. Finally, fatigue lives, crack shape evolution and final crack length were predicted assuming an initial crack size and considering that the crack maintains a quarter-elliptical shape. The comparison with experimental fatigue lives indicated the presence of initial defects larger than the silica particles; however, these large sizes can be explained by the residual stresses measured near the hole.

Determination of Elastic Properties by Resonant Technique: A Sensitivity Analysis

The in-plane elastic properties of materials can be determined using an experimental-numerical procedure based on the resonant frequencies of thin beams and plates. The objective of this paper is to study the accuracy of the material constants obtained with this technique. The procedure is presented and the parameters affecting its accuracy are identified. Specimens of epoxy reinforced with carbon fibers and 6082-T6 aluminum alloy were produced and experimental work was developed to obtain resonant frequencies in free-free boundary conditions. A numerical procedure based on FEM was developed replicating the experimental procedure and was used for a sensitivity analysis on the numerical and physical parameters. A great sensitivity relative to geometry was found, which emphasizes the need for ideally shaped specimens and accurate measurements. The influence of elastic properties on resonant frequencies is comparatively lower and varies quite considerably with geometry. The accuracy of experimental frequencies and specific mass was found to have a great impact on material constants.

Effect of water and fiber length on the mechanical properties of polypropylene matrix composites

This paper presents the results of a current study on polypropylene matrix composites processed by injection, with two different glass fiber lengths and five different volume fractions. Physical and mechanical properties were obtained, namely flexural strength, stiffness modulus and fracture toughness. The mechanical properties of the composites increased significantly with the increase of the fibers volume fraction in agreement with the Counto model. The effect of water immersion time was also analysed. Immersion in water promotes a marked decrease in mechanical properties in the early seven-ten days, and afterwards tends to stabilize. Water causes a decrease of the relative strength which increases with fiber volume fraction and reaches about 29 % and 32 % for 20 % of 4.5 mm fiber length and for 25 % of 12 mm fiber length respectively, after 28 days immersion in water. Fracture toughness increases with fiber volume fraction and is always higher for 12 mm fiber length composites than for 4.5 mm fiber length composites.

Viscoelastic Properties Assessment of Syntactic Foams by Dynamic Mechanical Analysis

Low-density sheet moulding compounds incorporating hollow glass micro-spheres are being increasing used namely in automotive industry, boats and deep-water submarines and core materials. This paper presents the results obtained in a current study of the viscous properties on hybrid short fibre/hollow glass microspheres composites fabricated with epoxy binder. Dynamic mechanical analysis (DMA) was used to study the effect of the filler volume fraction and of the addition of glass fibre reinforcement on the dynamic stiffness modulus, damping coefficient and glass transition temperature in tensile mode. The specimens were cut from plates produced by resin transfer moulding in vacuum with microspheres weight contents up to 13%. Elastic modulus decreases significantly with the increasing of filler volume fraction. In contrary, it increases significantly with the glass fibre reinforcement content. Glass transition temperature apparently tends to decrease with microspheres and of glass fibre reinforcement’s content. Tmax temperatures tend to increase slightly with the addition of fibre reinforcements and the microsphere filler. Maximum damping coefficient is much lower for the foams when compared with net resin.

Mechanical Properties of Woven Mat Jute/Epoxy Composites

Natural fibers combine technological, economic and ecological aspects. However, a major restriction on their successful use in long term composite applications is their high moisture absorption and poor dimensional stability. This paper is aimed at establishing a link between the mats grammage and the mechanical properties of the epoxy/jute fibers laminates. Composites reinforced by coarse, medium and fine (C, M and F) mats were processed by vacuum bagging. Some batches were immersed in water up to 60 days in order to study the hydro-degradation. Mechanical tests were performed to obtain the bending strength and impact response. The mechanical response to bending and impact loadings was conditioned not only by the percentage of fiber, but also by the thickness of the specimens, which leads to composites F having lower strength than composites C despite having a higher percentage of fiber. Immersion in water causes a marked loss of mechanical properties in the first days of immersion, especially for thinner fiber grammage composites. A strong influence of the mats grammage on the impact response was observed. Increasing mats grammage promotes a strong increase in peak load, restored energy and impact energy for perforation and also a marked reduction of the deformation.

Impact response of nano reinforced mat glass/epoxy laminates

The present work intends to characterize the effect that nanoclay and carbon nanotubes matrix reinforcements have on low velocity impact response of epoxy/glass fiber composites. The composite matrix used was the epoxy resin Biresin® CR120 combined with the hardener CH120-3 and the fiberglass triaxial mats ETXT 450. The results of the present paper are discussed in terms of load-time, load-displacement, energy-time diagrams and damage. The incorporation of nanoparticles produces only small improvement of the impact response in terms of the peak load and specific recovery energy. Peak load decreases slightly with increasing percentage of nanoparticles reaching a maximum decrease of 6 % for 3 wt% of nanoclays. Specific recovery energy increases in comparison with control formulation, around 14–18 % for 0.5 wt% addition of nanotubes and 7–15 % for 1 wt% of nanoclays, respectively. Specific recovery energy tends to decrease for higher percentages of nanoparticles in consequence of its poor distribution. Damaged area apparent shows a small reduction with nanoparticle content.

Assessment of the mechanical properties of nanoclays enhanced low Tg epoxy resins

The mechanical properties of the nanocomposites are dependent, not only of the clays content but, also, of the resin type and manufacturing process. In this context, the present study intends to develop a systematic study involving a low glass transition temperature (Tg) and low permeability epoxy resin (SR 1500 and the hardener SD 2503) with a commercially Nanomer I30 E nanoclays. Two dispersion processes were compared (direct (DM) and indirect method (IDM)) in terms of mechanical properties, as well as the influence of nanoclay content and hydro aging effect. It was possible to observe that the composites obtained by the indirect method present lower mechanical properties than the neat resin because there is residual acetone. For DM composites the tensile strength, fracture toughness and the specific energy absorbed by impact decreases with the reinforcement content, caused by particle agglomerates. Elastic modulus, at 25 °C, increases significantly and Tg increases slightly with the addition of nanoclays. Hydro aging promotes a progressive decreasing of the tensile strength and fracture toughness, with the clay content, reaching about 15 % and 7 %, respectively, for 6 wt% of nanoclays. On the other hand, a small increasing on specific energy absorbed was observed.

Effect of the Foam Core Density on the Bending Response on Sandwich Composites

This paper presents the results of a current study of sandwich panels manufactured by using homogeneous and multilayer core foams with the purpose of improving specific flexural stiffness modulus. In the present study, the core foams were produced by using Verre ScotchitTM-K20 hollow microspheres manufactured by 3M and the selected binder resin was epoxy 520 with hardener 523. The skin was a 2 mm thick carbon/epoxy laminate. The ARAMIS technique was used as an alternative technique to obtain accurate displacement fields. It was concluded that the multilayered panels with different loads of microspheres, putting higher percentage of microsphere in the center and lower in the outer layers, have also higher resistance and stiffness than the panels with homogeneous microsphere percentage cores. It was observed that both properties have a tendency to increase when the displacement rate increases from 0.5 mm/min to 10 mm/min for all architectures. Experimental stiffness agrees well with analytical model predictions.

HIGH‐PRESSURE RANGE SHOCK WAVE DATA FOR SYNTACTIC FOAMS

Syntactic foams [SF] are a porous composite material resulting from the mixture of Hollow Glass Micro Spheres [HGMS] with a polymeric binder. Beyond a set of technological advantages over the polymer considered alone, SF present as an essential feature the possibility to control in wide limits the amount, the shape and the size of the pores and for that reason are being used for benchmarking in the area of shock wave [SW] behavior of porous materials. In this paper, SW loading experiments of SF samples were performed in order to assess the high‐pressure range Hugoniot equation of state as a function of the SF initial density. Hugoniot data were assessed coupling the SW velocity within the SF samples with the SW velocity in a reference material or with manganin gauge results. The results obtained present a significant variation with the initial specific mass and can be described with appreciable precision by the Thouvenin/Hofmann Plate Gap model, while the concordance between the experimental results and the Gruneisen model seems to be very dependent on the Gruneisen coefficient values.