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To improve the stretch-bend forming precision of aluminum alloy profiles with complex open sections, the relationship stress–strain distribution and the spring-back radius variation were analyzed under different stretch-bend stages. Numerical simulation was performed on the auxiliary mold stretch-bend and spring-back process for the L-section aluminum alloy profile with variable curvature. The effects of cover plate pressure and baffle gap on residual stress, section deformation and spring-back value after forming were investigated. The results show that the stretch-bend warpage can be avoided by setting the cover plate on the straight section of the profile web plate. With the increase of the cover plate pressure, the section distortion of the vertical plate increases by 82%, and the maximum spring-back increases by 71%. A baffle plate was added to the outside of the vertical plate, and the baffle gap is proportional to the amount of section distortion and inversely proportional to the spring-back value. The critical cover force (1 kN) and the critical baffle gap (1 mm) obtained by numerical analysis are used in the stretch-bend forming experiment, and the maximum error between the two results is 2.39%. The numerical simulation has a certain reference value for the rational design of the auxiliary mold stretch-bend process parameters.

Section distortion is a common defect in plastic forming, however, excessive section distortion will affect the actual use of the workpiece. In this paper, the finite element software ABAQUS is used to simulate the multi-point flexible stretch-bending process. Processing parameters are important factors in the forming process of the profile, so this paper discusses the effects of three processing parameters, namely the effects of pre-stretching amount, pro-stretching amount and friction coefficient on section distortion under different bending radius, taking the complex cross-sectional T-profile as an example. And the validity of the simulation results is verified by comparing with the experimental results and the simulation results. At the same time, the upper limit value of section distortion is given according to the actual assembly and use of aluminium profile components of high-speed train head frame, and the minimum bending radius (i.e., processing limit) for which the section distortion does not exceed the given value under different process parameters is explored and used for practical production guidance. [ABSTRACT FROM AUTHOR]

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Abstract: A new formulation of the Generalized Beam Theory (GBT) that coherently accounts for shear deformation is presented in this paper. In particular, a modified formulation of the kinematics early proposed by Silvestre and Camotim for shear deformable GBT is devised. The new formulation, which preserves the general format of the original GBT for flexural modes, introduces the shear deformation along the wall thickness direction besides that along the wall midline, so guaranteeing a coherent matching between bending and shear strain components of the beam. According to the new kinematics, a reviewed form of the cross-section analysis procedure is devised, based on a unique modal decomposition for both flexural and shear modes. Much attention is posed on the mechanical interpretation of the deformation parameters in the modal space. It is shown that, in the modal space, it is possible to clearly distinguish bending deflections from deflections due to shearing strains, and to recover classical beam degrees of freedom and standard beam theories as special cases. The effectiveness of the proposed approach is illustrated on two typical benchmark problems. [Copyright &y& Elsevier]

Abstract: Histologic sections of arteries can be used to generate three-dimensional (3D) geometric models and identify structural constituents. However, geometric distortions are introduced by fixation, embedding and sectioning; distortions which can, for example, lead to errors in stresses predicted by finite element models. We developed a method to measure and correct for distortions caused by acrylic processing and applied it to intact, healthy porcine coronary arteries. Micro-computed tomography was used to image arteries in the fresh and embedded states. Tissue blocks were sectioned, stained and imaged using a light microscope. Each section contained four registration marks used to determine strains introduced by sectioning and staining. Using these three image sets, 3D geometric models were generated and distortions were measured. Fixation, processing, and embedding resulted in shrinkage of 6.4±2.3% axially and 35.4±5.0% in mean cross-sectional area (). Shrinkage in a cross section was well characterized by a uniform, equibiaxial strain. Sectioning and staining resulted in additional compressive strains in the sectioning direction of 0.067±0.011 and, in the direction perpendicular to sectioning, of 0.023±0.005 (). These strains are assumed uniform and form the basis for correcting section geometry. Reconstructions using corrections for sectioning and shrinkage-related distortions had errors of 1.6±0.5% () and 4.0±1.7% (), respectively. [Copyright &y& Elsevier]

Curvature spring-back and section distortion are the primary quality defects of bent sections. Experiments on LY12M hat-section profiles have been made using a rotary draw bending machine, with the aim of determining the influence of the number of rotary draw bending cycles on curvature spring-back and section distortion. In order to enhance the part quality and improve the production efficiency, the authors demonstrate the method of imposing a stretching force and a mold-repair angle, thus, reducing the number of rotary draw bending cycles. By means of experiment on a rotary draw bending machine with a stretching force, the best side pressure, stretching force and appropriate mold-repair angle are determined, which reduces the number of required rotary draw bending cycles to 2. Satisfactory parts have been made by this technique. [Copyright &y& Elsevier]

Lateral torsional buckling (LTB) and local section distortion of pultruded glass fiber reinforced polymer (GFRP) I-sections subject to flexure are investigated. LTB behavior will dominate longitudinally slender beams having low flange slenderness. However, as the flange becomes more slender and/or the beam shorter, the effects of local section distortion (LSD) become significant, reducing the LTB capacity of the member. Using the energy method, an analytical study was conducted and explicit equations for predicting the critical LTB buckling moments of GFRP I-sections accounting for the effects of LSD are proposed. The proposed LTB equation was validated using experimental results and finite element analysis. Excellent agreement was observed between the proposed LTB equation and experimental results for sections expected to be dominated by LTB behavior. Extending the study using the same approach, an equation predicting LTB capacity as it is affected by LSD was also validated using experimental results. It is found that the proposed LTB equation captures the capacity reduction due to LSD and therefore, provides more accurate predictions for sections expected to be dominated by LSD behavior; those having small slenderness ratios and large flange slenderness ratios. [ABSTRACT FROM AUTHOR]