Search

Mechanical properties considerably reduce in wood-plastic composites (WPCs) due to the use of wood particles, so the structural applications of these composites are scarce. Thus, embedding continuous fibers is considered the most reliable method for increasing mechanical properties, although there are still challenges in employing this method on a large scale. In this study, an elaborated, special modular die with the capability of adjusting 14 rovings of continuous fibers was designed, manufactured, and implemented to simultaneously embed continuous glass fibers into the extruded WPC profile. More precisely, it was aimed to investigate the arrangement of fiber rovings into the desired positions in a WPC profile of 70 wt% wood content. Also, the effect of the glass bundle tex (at three level, 1200,2400 and 4800) and the fiber position (at four levels, 0, 2, 4, and 6 mm of relative movement of the guides) on the mechanical properties of WPCs was evaluated. According to the results, the flexural strength of reinforced specimens for 1200, 2400, and 4800 texes increased by 85.8, 107, and 159.7%, respectively, compared with the non-reinforced composite. Theoretical values were calculated and compared with experimental outcomes. Based on the results, The failure mode was non-catastrophic, which means the specimens were able to carry partial loading; a desirable characteristic for the structural applications.

In spite of product quality increase in the cold roll forming process by previous practical researches for defects prevention, there are some ill-considered defects such as over-bending, which diminished the product quality in the open section products of this process. This defect which happens by superfluous bending of sheet in the forming stand not only lead to defective products, but also trigger other defects such as edge wrinkling. Since in an elaborate process such as cold roll forming, forming parameters play an active role in defect prevention, the effect of some important parameters is investigated on the over-bending defect and product bending angle by doing 68 experimental tests and numerical simulations in the present study. The list of parameters which are investigated includes bend angle increment, flange width, strip thickness, radius of bend, strength of the materials, and inter-distance between successive stands. In addition, the reason behind the effect of each parameter on the accuracy of the bending angle is laid out. Results show that over-bending defect can be compensated or even eliminated by decreasing the bending angle in each stand, a technique called bending angle increment. Increasing the number of forming stands from two to five causes the over-bending to decrease from 6° to 0°. With bending angle increment being the most impactful factor, bending radius, flange width, and strip thickness have a decreasing impact on over-bending. This study also brings forward a reverse relationship between the strength of the material and the intensity of over-bending. The inter-distance between successive stands was found to have the least effect on over-bending. Results highlight the importance of pre-form rolls at the beginning of the roll forming line. Without the usage of pre-form rolls, the folding of strips on a 60° angle, cannot be done in one stand.

This research is focused on the modeling of the deformation behavior of thin austenitic stainless steel sheets to consider size effect in microscale. First, the material with two different thicknesses is heat treated to obtain different grain sizes, and then they are characterized by the uniaxial tensile tests. The experimental results show that flow stress decreases with the reduction of the sheet thickness and the increase of the grain size. The decline of the flow stress curve is associated with the decrease of the strength coefficient and increase of the hardening exponent as the plastic deformation is scaled down to the microscale. To better model the behavior of the material in the microscale, a new constitutive model is proposed based on the Swift equation to take into account the geometry and grain size effect. This model is also defined in the finite element model of the uniaxial tensile test. It is found that the flow stress curve predicted by the proposed constitutive model shifts down by the decrease of the number of grains across the thickness, which are consistent with the experimental results. In addition, the finite element model with the proposed constitutive model predicts accurately the deformation load in the uniaxial tensile tests. It can be concluded that the proposed constitutive model can provide a good description of the flow stress by considering the interactive effect of specimen and grain sizes and can be used in the modeling of material behavior in microforming processes.

Fracture is one of the limiting factors of sheet metal forming processes. For this reason, finite element simulations are widely used for providing suitable forming approaches. However, the success of these approaches depends on the correct modeling of fracture in the simulations. In this paper, the fracture behavior of the Aluminum 6061-T6 sheet in the U-bending process is investigated by applying the Gurson–Tvergaard–Needleman model. For this purpose, the Gurson–Tvergaard–Needleman model is defined in the ABAQUS software by means of a proper subroutine. The Gurson–Tvergaard–Needleman model is also modified to take into account the anisotropy effect on the yield surface and the damage evolution due to shear stresses. Then, the proposed models are calibrated using the inverse analysis method based on tension tests with different stress states. The deformation mechanics analysis reveals that considering the normalized Lode angle parameter in the damage function increases the accuracy of fracture prediction, especially in low-stress triaxiality. Comparing the predicted fracture displacements with the experimental value in the U-bending process shows that the modified Gurson–Tvergaard–Needleman model calibrated by the uniaxial tension and in-plane shear tension tests can predict the onset of fracture with acceptable accuracy in the bending process while the original Gurson–Tvergaard–Needleman should be calibrated by a test with stress state close to that in the bending area to have such a result.

A study on new materials usage to produce fiber metal laminates is presented in this work. Amorphous polyvinyl chloride thermoplastic and aluminum 3550 sheets are used to fabricate the fiber metal laminates. Different surface treatments were carried out on the aluminum sheets and the fiber metal laminates were produced using the film stacking procedure. Flexural strength and modulus of the products and also shear strength of bonding were measured using three-point bending test, and their failure mechanisms were evaluated using optical microscope images. Also, the effects of aluminum layer and aluminum/composite laminates bonding on the dynamic properties of the fiber metal laminates were studied using Dynamic Mechanical Thermal Analysis. It was concluded that mechanical roughening of the aluminum sheet has the maximum effect on the aluminum/matrix bonding strength such that simultaneous fracture of composite laminates and aluminum layer in the bending condition was observed in the produced fiber metal laminates without any delamination.