We evaluated amorphous silicon thin-film transistors (TFTs) fabricated on polyimide foil under uniaxial compressive or tensile strain. The strain was induced by bending or stretching. The on- current and hence the electron linear mobility µ depend on strain as µ = µ0(1 + 26E), where tensile strain has a positive sign and the strain is parallel to the TFT source-drain current path. Upon the application of compressive or tensile strain the mobility changes "instantly" and under compression then remains constant for up to 40 h. In tension, the TFTs fail mechanically at a strain of about +0.003 but recover if the strain is released "immediately.

This paper presents the results of an experimental study of surface topology evolution that leads to crack nucleation and propagation in silicon MEMS structures. Following an initial description of the unactuated surface topology and nanoscale microstructure of polysilicon, the micromechanisms of crack nucleation and propagation are elucidated via in situ atomic force microscopy examination of cyclically actuated comb-drive structures fabricated from polysilicon. It is found that the surface of the polycrystalline silicon MEMS undergoes topological changes that lead to elongation of surface features at the highest tensile point on the surface. A smoothing trend is also observed after a critical stress level is reached.

We evaluated a-Si:H TFTs fabricated on polyimide foil under uniaxial compressive or tensile strain. The strain was induced by bending or stretching. All experiments confirmed that the on-current and hence the electron linear mobility depend on strain å as μ = μ0 (1 + 26·ε), where tensile strain has a positive sign. Upon the application of stress the mobility changes instantly and then remains unchanged in measurements up to 40 hours. In the majority of the TFTs the off-current and leakage current do not change. In tension, the TFTs fail mechanically at a strain of ∼ 3x10-2 but recover if the strain is released ‘immediately’.

The implications of the results of recent experimental and numerical investigations of the propagation of single and multiple configurations of semi-elliptical cracks are assessed for the prediction of fatigue life in structures and components in service. Simplified methodologies for the assessment of the effects of crack closure and stress state on the propagation characteristics of semi-elliptical cracks are proposed, and numerical techniques for the analysis of coplanar and non-coplanar configurations of semi-elliptical cracks are also presented. These include the results of finite element and simplified fracture mechanics analyses in which crack growth was computed on a step-by-step basis from the Paris equation.

A probabilistic multiparameter approach is presented in this paper for the prediction of the combined effects of multiple variables on wear rates in the material of agricultural sprayer nozzles. The methodology developed is based on the principles of stochastic processes in mathematical statistics, which essentially involve the statistical formulation of the mathematical models of wear rates as functions of the multiple random variables that may affect agricultural sprayer nozzle wear rates, and the determination of the constants of the probabilistic model using multivariate regression analysis. A general empirical approach is proposed for the estimation of nozzle wear rate. The predictive capacity of the empirical approach is then verified by comparing the relevant theoretical model predictions with experimental data. When this exercise was carried out, excellent correlations were obtained between theoretical model predictions and experimental data. An important feature of the model is that assessments can be made for the relative contribution of the effect of each random variable on the total wear rate at any point in time. The importance of the new multiparameter models and the interdisciplinary collaboration of experts in the fields of structural materials, mechanics, and probabilistic methods in order to control and minimize wear rates in the design of nozzles for food production and agricultural engineering applications are also discussed.