Stress‐initiated void formation during cure of a three‐dimensionally constrained thermoset resin

During cure of epoxy resins, polymerization induces an increase in mechanical properties, which is accompanied by a volumetric shrinkage. When the resin is cured in a constrained mold to which it adheres, tensile stresses will hence develop, which may exceed the stremgth of the resin at a given curing stage. Voids will then form. The origin and governing parameters of void formation are studied using an epoxy resin cured in a three‐dimensionally constrained glass mold following isothermal cure cycles. Two types of voids are shown to appear during cure, one early in the process and a second around the gelation point. A viscoelastic analysis of the material stress state over the whole range of cure is performed. Both the viscoelastic modulus obtained from a time‐cure‐temperature superposition and the volumetric shrinkage, which was continuously measured by density change, are taken into account. A value for the critical internal stress at void initiation is thus proposed. This criterion can be used to provide guidelines for tailoring the material properties toward an increase of the critical stress for void initiation. Also, since during theprocessing of composite materials, cases may arise where the resin cures within the interstices left between consolidated fibres that do not move, this critical stress failure criterion can be of use in the eastablishment of a process window providing guidelines for the production of void free composites.     

Impact localisation with FBG for a self-healing carbon fibre composite structure

We demonstrated the localisation of impacts in orthotropic carbon fibre reinforced polymer (CFRP) composite materials to within a few centimetres, using a sparse array of fibre Bragg grating (FBG) sensors. This type of sensor is easily embedded in composites permitting the development of structures with integrated sensing capability. Impact location was determined by measuring the differences in time-of-flight of ultrasonic Lamb waves at three surface-mounted sensors. An algorithm was developed taking into account the angle dependence of the optical fibre sensor sensitivity and the variation of Lamb waves propagation velocity with direction and wave mode. The performance of FBG sensors for impact localisation was compared to that of standard piezoelectric transducers (PZTs), which are already widely used for that purpose. The FBG-based system showed promising potential for a non-intrusive impact detection system applied to self-healing composite structures.     

A Microscope-Based Particle Counting System for Determining Collected Aerosol Mass During the Calibration of a Cascade Impactor

It is shown that a simple optical particle-counting system can be efficiently and accurately used for determining the mass of collected particles during the calibration of a cascade impactor. For particles larger than 1 mu m in diameter, the limit of detection was enhanced by a factor 5 compared to the traditional spectrophotometer-based method.     

Performance of self-healing epoxy with microencapsulated healing agent and shape memory alloy wires

We report the first measurements of a self-healing polymer that combines a microencapsulated liquid healing agent and shape memory alloy (SMA) wires. When a propagating crack ruptures the embedded microcapsules, the liquid healing agent is automatically released into the crack where it contacts a solid catalyst embedded in the matrix. The SMA wires are then activated to close the crack during the healing period. We show that dramatically improved healing performance is obtained by the activation of embedded SMA wires. We conclude that improved healing is due to a reduction of crack volume as a result of pulling the crack faces closed, and more complete polymerization of the healing agent due to the heat produced by the activated SMA wires.     

The effect of processing conditions on the morphology, thermomechanical, dielectric, and piezoelectric properties of P(VDF-TrFE)/BaTiO3 composites

In this study (0–3) P(VDF-TrFE)/BaTiO₃ composites containing up to 60 vol% of ceramic phase were prepared by solvent casting or compression molding. Their thermomechanical, dielectric, and piezoelectric properties were investigated, and discussed in the light of the properties of the basic components, the processing route and the resulting morphology. The crystalline structure of the P(VDF-TrFE) matrix was found to be highly dependent on the processing route, while the structure of BaTiO₃ was not affected by any of the processing steps. The mechanical properties of the solvent cast materials showed a maximum at 30 vol% BaTiO₃, while they increased monotonically with BaTiO₃ content for compression molded materials. This difference was attributed to a higher amount of porosity and inhomogeneities in the solvent cast composites. Permittivity as high as 120 and piezoelectric coefficient d ₃₃ up to 32 pC/N were obtained for compression molded composites, and the observed decrease in d ₃₃ with aging time was attributed to the effect of mechanical stress release in the polymer matrix.     

Effects of nonstructural carbohydrate concentration in alfalfa on fermentation and microbial protein synthesis in continuous culture

Insufficient readily fermentable energy combined with extensive degradation of proteins in alfalfa (Medicago sativa L.) may result in poor forage N utilization by ruminants. Using the inherent genetic variability and differences between harvests, our objective was to compare the effect of contrasting concentrations of nonstructural carbohydrates (NSC) in alfalfa on rumen fermentation and microbial protein synthesis. Individual genotypes of the alfalfa cultivar AC Caribou grown near Québec City, Québec, Canada, were harvested at the vegetative and early flowering stages, dried at 55°C, ground, and analyzed for soluble carbohydrates (fructose + sucrose + glucose + pinitol) and starch. Approximately 20 genotypes having, respectively, the highest and lowest NSC concentrations were pooled to constitute 2 contrasted 1-kg forage samples. Samples of high- (17.9% DM) and low- (7.4% DM) NSC alfalfa were respectively allocated to separate dual-flow fermenters in a completely randomized design with 3 replications. Rumen inoculum was obtained from 4 ruminally fistulated cows in early lactation that were fed a TMR with a 50:50 forage to concentrate ratio. A 10-d incubation period was used, with the first 6 d serving as an adaptation period followed by 4 d of sampling with solid and liquid dilution rates in the fermenters set at approximately 2.0 and 4.3%/h, respectively. High versus low NSC concentration in alfalfa significantly enhanced the apparent digestibility of OM (59.1% for high-NSC alfalfa vs. 54.4% for low-NSC alfalfa) and DM (60.0 vs. 54.3%) and the true digestibility of DM (74.1 vs. 64.7%). Increasing NSC concentration in alfalfa (high vs. low) significantly decreased ruminal pH (6.85 vs. 7.08) and NH₃-N concentration (26.0 vs. 33.6 mg/dL) and increased total VFA concentration (94.9 vs. 83.0 mM). Molar proportions of acetate, isobutyrate, and isovalerate significantly decreased, whereas molar proportions of propionate and butyrate significantly increased with high-NSC alfalfa, resulting in a more glucogenic fermentation. More importantly, microbial N flow (263 vs. 230 mg/d) and bacterial N efficiency (41.1 vs. 29.6% of available N), measured using ¹⁵N as a microbial marker, both significantly increased with the high-NSC alfalfa. These results indicate that increasing the concentration of NSC in alfalfa promotes a glucogenic fermentation and enhances microbial N synthesis in the rumen.     

Evaluating the market transformation impacts of a DSM program in the Province of Quebec

In 2006, Hydro-Québec introduced a large DSM program on the market to promote the adoption of compact fluorescent lamps in Québec households. After 3 years of program implementation, there was significant indication on the part of market actors that the promotional campaign component was quite effective in transforming the Québec market. Hydro-Québec therefore decided to modify its approach to program evaluation to include the quantification of market effects. Econoler led a team including American partners, Opinion Dynamics Inc. and Megdal & Associates to conduct an evaluation of program impacts on market transformation. An evaluation strategy was designed where different research tools would be integrated to determine market evolution over the two previous years. Each research method was used to determine an estimate of program impacts, then triangulated with other approaches to determine the most appropriate impact evaluation method regarding the Hydro-Québec program. Research efforts included a non-participant survey, interviews at manufacturer headquarters across Canada, interviews with banner distributor representatives across Canada, the collection of sales and market share data from manufacturers and retailers as well as secondary research to identify other players that could influence the market. The evaluation revealed that savings of 168 GWh could be attributed to direct and indirect impacts of the program for the 2006–2007 period.     

UV intensity,temperature and dark-curing effects in cationic photo-polymerization of a cycloaliphatic epoxy resin

A difunctional cycloaliphatic epoxy monomer was cationically photo-polymerized in the presence of a diaryliodonium salt photoinitiator and an isopropyl thioxanthone photosensitizer at different temperatures and UV intensities. The photo-polymerization kinetics and structure formation were analysed using photo-DSC, IR spectroscopy and photo-rheology. An autocatalytic relation was used to model the conversion state with Arrhenius and power-law relationships for temperature and light intensity dependence. Conversion was found to depend on sample thickness, following the Beer–Lambert law. Photo-rheology measurements showed that the system vitrified before gelation at ambient temperature, and after gelation at high temperature under intense UV illumination. Time temperature transformation and time intensity transformation diagrams were built. Moreover, isothermal dark-curing enabled significant conversion increases up to the occurrence of vitrification, while thermal post-curing above T_g led to conversion as high as 71%. Thermo-mechanical measurements enabled to quantify T_g and the effects of the increase in conversion provided by thermal post-curing.     

Microstructured Fibers for the Production of Food

Food engineering faces the difficult challenge of combining taste, i.e., tailoring texture and rheology of food matrices with the balanced intake of healthy nutrients. In materials science, fiber suspensions and composites have been developed as a versatile and successful approach to tailor rheology while imparting materials with added functionalities. Structures based on such types of physical (micro)fibers are however rare in food production mainly due to a lack of food‐grade materials and processes allowing for the fabrication of fibers with controlled sizes and microstructures. Here, the controlled fabrication of multi‐material microstructured edible fibers is demonstrated using a food compatible process based on preform‐to‐fiber thermal drawing. It is shown that different material systems based on gelatin or casein, with plasticizers such as glycerol, can be thermally drawn into fibers with various geometries and cross‐sectional structures. It is demonstrated that fibers can exhibit tailored mechanical properties post‐drawing, and can encapsulate nutrients to control their release. The versatility of fiber materials is also exploited to demonstrate the fabrication of food‐grade fabrics and scaffolds for food growth. The end results establish a new field in food production that relies on fiber‐based simple and eco‐friendly processes to realize enjoyable yet healthy and nutritious products.     

Going into the wild in child–robot interaction studies: issues in social robotic development

As robots move into more human centric environments we require methods to develop robots that can naturally interact with humans. Doing so requires testing in the real-world and addressing multidisciplinary challenges. Our research is focused on child–robot interaction which includes very young children, for example toddlers, and children diagnosed with autism. More traditional forms of human–robot communication, such as speech or gesture recognition, may not be appropriate with these users, where as touch may help to provide a more natural and appropriate means of communication for such instances. In this paper, we present our findings on these topics obtained from a project involving a spherical robot that acquires information regarding natural touch from analysing sensory patterns over-time to characterize the information. More specifically, from this project we have derived important factors for future consideration, we describe our iterative experimental methodology of testing in and out of the ‘wild’ (lab based and real world), and outline discoveries that were made by doing so.