Simplified model and analysis of a pair of coupled thermo-optical MEMS oscillators

Nonlinear Dynamics - Motivated by the dynamics of microscale oscillators with thermo-optical feedback, a simplified third-order model capturing the key features of these oscillators is developed,...     

Temperature and deformation measurements in transient metal cutting

Metal cutting is a thermomechanically coupled process in which plasticity induced heating and friction play a critical role. The objective of this work is to develop a methodology to understand and quantify this coupling. Temperatures of the workpiece and the chip during transient cutting processes are measured using a linear array of 16 InSb infrared detectors with 200 ns rise time and 27 μm spatial resolution. Three different materials, 1018 CR steel, Al6061-T6 and Ti-6Al-4V, are tested at a cutting speed of 4.3 m s⁻¹. A grid method is used to measure deformations during the above set of experiments. Measured values of temperature and deformation are compared to results of finite element simulations of the experiments.     

High Temperature Shear Strength of T650-35/HFPE-II-52 Polyimide Matrix Unidirectional Composite

The shear strength of a 4-ply unidirectional composite laminate consisting of carbon fibers (T650-35) and a polyimide matrix (HFPE-II-52) was measured over a temperature range of 25 to 315°C. The tests were performed using a Iosipescu test sample, modified to provide a more uniform shear stress distribution across the gauge section and loaded with an Arcan type test fixture. The test specimen design is based on the results of an extensive finite element study. Shear strength tests were performed on dry, 50% RH and 100% RH moisture saturated samples. Results of the experiment show that shear strength decreases from approximately 120 MPa at 25°C to 60 MPa at 315°C and that moisture saturated samples have a 5–10 MPa lower shear strength than dry samples.     

Memory of Chirality in Photochemistry

The helical-chiral character of the diradical intermediate 2 , which cyclizes quicker than it equilibrates, explains the memory effect of chirality that occurs during the enantioselective photocyclization of alanine derivative 1 to give the proline derivative 3 . Ts=H₃CC₆H₄SO₂.     

Effect of Hydration on Tensile Response of a Dual Cross-linked PVA Hydrogel

Experimental Mechanics - Little is known about the effect of water content on the mechanical properties of dual cross-linked hydrogels. To quantify the changes in the mechanical response and...     

Solution behaviour of a formate capped surfactant—the oxidation product of an alcohol ethoxylate

The solution behaviour has been investigated for an alcohol ethoxylate terminated with a formic acid ester. This compound has previously been reported to be an important degradation product in the auto-oxidation of alcohol ethoxylates. In this work we have investigated the solution behaviour of the formic acid ester surfactant C₁₂H₂₅(OCH₂CH₂)₄OCHO (C12E4---OCHO). The pure formate was found to be sparsely soluble in water with no clear point at 0.1%. The critical micelle concentration was found to be 129 μM at 35°C, compared to 50 μM for the parent surfactant C₁₂H₂₅(OCH₂CH₂)₅OH (C12E5). To mimic the behaviour of the oxidised surfactant, the formate was mixed in different ratios with C12E5 and the cloud point, surface tension and critical micelle concentration (cmc) of these mixtures were studied. The gradual increase of formate was found to shift the cloud point and isotropic regions to lower temperatures. The cmc of the mixture was found to be lower than for the pure surfactant. The favourable interaction was analysed according to the non-ideal model by Rubingh and the interaction parameter, β, was determined to be −4±0.53, which is unusually large for a mixture of two non-ionic surfactants. These results indicate that the reduction of cloud point observed during oxidation of non-ionic surfactants can in part be attributed to the formation of formate esters.