Structural adhesive joints were subjected to high loading rates in mode I and their resulting fracture behaviour was studied in detail. Joints were formed between unidirectional carbon-fibre epoxy composites and between aluminium-alloy substrates bonded with a tough, hot-cured, single-part epoxy adhesive. In all the tests described in the present paper the joints failed by a crack propagating cohesively through the centre of the adhesive layer. Double cantilever beam (DCB) and tapered double cantilever beam (TDCB) tests were performed, from quasi-static loading rates up to 15 m/s, and a test rig was developed incorporating high-speed video acquisition for the high-speed tests. A detailed analysis strategy, and associated equations, were developed to account for (i) the types of different fracture behaviour regimes encountered, (ii) the dynamic effects in the test data, and (iii) the contribution of kinetic energy to the energy balance. Using the above analysis strategy and associated equations, increasing the test rate over six decades (from 10-5 to 10-1 m/s) was found to lead to a reduction in the value of the adhesive fracture energy, GIc, by about 40% of its quasi-static value, i.e. from 3500 to about 2200 J/m2. Further, at quasi-static loading rates, the measured adhesive fracture energies were independent of substrate material and test geometry (i.e. DCB or TDCB). However, at faster loading rates, the TDCB tests induced higher crack velocities for a given loading rate compared with the DCB test geometry, and neither the test rate nor the crack velocity were found to be the parameter controlling the variation in GIc with increased test rate. Thus, an isothermal-adiabatic model was developed and it was demonstrated that such a model could unify the DCB and TDCB test results. Indeed, when the GIc values, determined from the analysis strategy and associated equations proposed, were plotted as a function of 1Ntime, where the time, ti, was defined to be from the onset of loading the material to that required for the initiation of crack growth, the results collapsed onto a single master curve, in agreement with the isothermal-adiabatic model.
Summary Recently increased attention has been given to the utilization of agricultural waste products to produce food, feed, fertilizer and as a raw material in certain industries. Such utilization could not only help maximize available resources but at the same time minimize waste disposal problems. Nutritional and oil characteristics of different seeds were investigated. On a dry basis protein contents of 43, 34, 16.1 and 36.9% and oil contents of 19, 50.6, 35.9 and 25.7% were found in maple, pumpkin, citrus and apple seeds, respectively. Determined food energy values averaged 626 kcal/100 g (26.2 kJ/g). The seeds were found to have valuable amounts of essential minerals. The major fatty acid composition was 18 : 2 (linoleic) at concentrations of 39.1, 58.9, 31.9 and 45.6% and total saturated fatty acids of 16.8, 19.7, 42.8 and 12.4% and cis, cis ‐PUFA contents were 34.1, 46.8, 19.8 and 45.6%, respectively, for maple, pumpkin, citrus and apple; no measurable amounts of trans fatty acids were found.
Abstract Solid fat content of shortening and margarine was estimated by pulsed NMR. These values were compared with those of the melted fats using different cooling methods. Solid fat content of shortenings measured at 10 and 20 C followed the same trend as those measured on the melted fat tempered at 30 C. Solid fat content of margarines followed the same trend as those measured on the nontempered fats. Softening points of the products were similar to the dropping points of the fats, as were the temperatures of the DSC major melting peaks. Compression tests of cylindrical samples provided more information about textural characteristics of the products than one penetration tests.
Direct placement restorative materials must interface with tooth structures that are often compromised by caries or trauma. The material must seal the interface while providing sufficient strength and wear resistance to assure function of the tooth for, ideally, the lifetime of the patient. Needed are direct restorative materials that are less technique-sensitive than current resin-based composite systems while having improved properties. The ideal material could be successfully used in areas of the world with limited infrastructure. Advances in our understanding of the interface between the restoration adhesive system and the stages of carious dentin can be used to promote remineralization. Application of fracture mechanics to adhesion at the tooth-restoration interface can provide insights for improvement. Research in polymer systems suggests alternatives to current composite resin matrix systems to overcome technique sensitivity, while advances in nano- and mesoparticle reinforcement and alignment in composite systems can increase material strength, toughness, and wear resistance, foreshadowing dental application.
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