Van Ngan Lê

Effects of Large Deflection on Mode II Fracture Test of Composite Materials

Large deflection response and its effect on measuring the Mode II fracture toughness of composites have been studied for the End-Loaded-Split (ELS) test. The response is analyzed by nonlinear beam theory and the correction to toughness calculation based on linear beam theory is obtained for any crack length. The effect of large deflection on accuracy of load measurement is also studied. In addition, the ELS test is used to measure the Mode II toughness of carbon fiber/polyetheretherketone (PEEK) composite. It is found that the data reduction procedure based on linear beam theory needs to be corrected if the fracture occurs at large deflections. Special care should also be taken towards a valid load measurement when using the ELS test in the large deflection range.

Safety factor of welded-plate beams based on finite element linear buckling analysis

Beams made of welded plates are very common thanks to the optimum combination of weight and strength of structure. One of the most important design criteria of these beams is their safety against lateral buckling and local buckling. Linear buckling analysis by Finite Element Method (FEM) quickly gives the load multiplier factor to produce elastic buckling. This factor could be considered as the safety factor against buckling if membrane compression stresses in the most critical zone remain well below yield stress up to the buckling load. Otherwise, this interpretation could become unsafe because the combined membrane plus bending stresses in critical zones, which are neglected in linear elastic analysis, could exceed the yield stress. A correction procedure must then be used and may be summarized into the following steps: (1) Carry out a linear static FEM analysis followed by a linear buckling analysis for calculating the lowest load multiplier factor « f » to produce elastic buckling of the E structure; (2) Identify the most critical zone of the buckling mode 1 and its width “b” ; (3) Check the results of static analysis and identify the value « σmeqvL » which stands for « membrane equivalent stress linearized over the buckled width »; (4) Calculate the so called « elastic buckling stress » by ScrE = fE*σmeqvL ; (5) If ScrE is low enough, accept Scr = ScrE as the critical stress or else correct the critical stress Scr by a correction procedure to be defined by considering plastic deformation due to bending across the thickness in critical zones prior to buckling; (6) Calculate the safety factor against buckling by standard formula f = Scr/σmeqvL. In a similar philosophy of Johnson’s empirical formulas for short columns, the summarized procedure is successfully applied in this paper to numerical examples of thin and moderately thick welded-plate beams for correcting the load multiplier factor given by FEM. Numerical example results show that the proposed correction procedure, or a similar one, is a must-do step after obtaining results of linear buckling analysis by FEM, because the multiplier factor given by FEM could be unsafe or even dangerous for some weldedplate beam designs.

EFFECTIVE LEARNING OF BUCKLING OF COLUMNS IN ENGINEERING PROGRAMS

The objective of this study was to use mentalmaps to analyze the design of higher education students ontheir understanding of technology. The courses wereworked: Computer Science, Technology Systems for InternetTechnology in Computer Networks and Technology Analysisand Systems Development, in particular, was working thirdyearstudents of the Course of Computer Science andstudents of the early years of technological courses. Just asscience, technology is evolving more and more, bothevolving categories irreversible, we must haveunderstandably o of its strengths and weaknesses in society,so we have to think and understand the movement CTS.Index Terms ⎯ mental maps, uniformity and education.

Waving behaviour of fatigue stress fluctuation in shrink-fit assemblies using 3D finite elements

High bearing load roller shafts are made of high performance steels as they are subjected to severe fatigue conditions, which combine a shrink-fit load and a rotating bending. Alternating stress intensity for fatigue analysis under said conditions, using elastic and maximum shear stress theories, shows a waving behaviour within a short distance near the contact edge. This discovery is observed by using structured 3D finite element models with surface-to-surface contact and element sizes varying from a coarse size far from the contact edge down to the order of sliding displacement near the contact edge. These FE models provide proof that stresses near the contact edge increase indefinitely when element size reduces. It is also found that the maximum alternating stress intensity at the depth of one ten-thousandth of the shaft diameter, using the friction coefficient of 0.01 in FE models, gives a good comparison with empirical fatigue data of classic shrink-fit assemblies for a wide range of geometry and loading.