Faculty of Engineering and Built Environment
Permanent URI for this communityhttp://ir-dev.dut.ac.za/handle/10321/9
Browse
2 results
Search Results
Item Buckling and sensitivity analysis of nonlocal orthotropic nanoplates with uncertain material properties(Elsevier, 2014) Radebe, Isaac Sfiso; Adali, SarpAccurate estimates of the orthotropic properties of nano-materials are usually not available due to the difficulties in making measurements at nano-scale. However the values of the elastic constants may be known with some level uncertainty. In the present study an ellipsoidal convex model is employed to study the biaxial buckling of a rectangular orthotropic nanoplate with the material properties displaying uncertain-but-bounded variations around their nominal values. Such uncertainties are not uncommon in nano-sized structures and the convex analysis enables to determine the lowest buckling loads for a given level of material uncertainty. The nanoplate considered in the present study is modeled as a nonlocal plate to take the small-size effects into account with the small-scale parameter also taken to be uncertain. Method of Lagrange multipliers is applied to obtain the worst-case variations of the orthotropic constants with respect to the critical buckling load. The sensitivity of the buckling load to the uncertainties in the elastic constants is also investigated. Numerical results are given to study the effect of material uncer- tainty on the buckling load.Item Minimum weight design of beams against failure under uncertain loading by convex analysis(Springer, 2013-01-29) Radebe, Isaac Sfiso; Adali, SarpUnder operational conditions, some loads acting on a beam are known (deterministic loads), but there usually exist other loads the magnitude and distribution of which are unpredictable (uncertain loads). If the uncertainty in the loading is not taken into account in the design, the likelihood of failure increases. In the present study beams are designed for minimum weight subject to maximum stress and buckling load criteria and under deterministic and uncertain transverse loads. The uncertain load, which is subject to a constraint on its L 2 norm, is determined to maximize the normal stress using a convex analysis. The location of the maximum stress is determined under the combination of deterministic and worst-case uncertain loads. The minimum weight design is obtained by determining the minimum cross-sectional area subject to stress and buckling load constraints. Results are given for a number of problem parameters including the axial load, elastic foundation modulus and uncertainty levels.