وحید زال

In this study, the phenomenon of ductile fracture in single-stage roll forming processes was investigated. In this regard, the fracture behavior of the 6061-T6 aluminum alloy was examined using the Modified Mohr-Coulomb fracture criterion. Subsequently, the calibration of the fracture criterion was carried out using a combined experimental-simulation approach. The roll forming process was modeled using finite element analysis, and the fracture criterion was implemented within the appropriate subroutine of the finite element simulation. According to the results, the Modified Mohr-Coulomb criterion with a 4.47% error capability could predict the onset of fracture in the single-stage roll forming process. Considering the sensitivity of the damage distribution accuracy to the stress state during the process, the effects of process parameters including thickness, bending angle, and corner radius on the triaxial stress parameter were investigated. The results indicate that these parameters do not have a significant impact on the triaxial stress parameter, and its average value remains within the range of 0.057 throughout all cases. Therefore, the fracture prediction results obtained with this criterion can be extended to other roll forming scenarios. Based on this, the influence of process parameters on damage and fracture during the roll forming process was examined. According to the results, an increase in sheet thickness and bending angle leads to an increase in damage, while an increase in the corner radius results in a reduction in damage area and a delayed occurrence of fracture during the process

In this article, the effect of filling foam on the energy absorption capability of hybrid tubes with different thicknesses of the composite layer has been investigated experimentally. For this purpose, 10 aluminum/woven glass fiber/polyester resin hybrid tubes with 5 different thicknesses of the composite layer between 0 and 1.75 mm were produced by manual tape winding on an aluminum tube with an outer diameter of 42 mm and a thickness of 1 mm, then, 5 of these tubes were filled with polyurethane foam with free density of 40 kg/m3. Afterwards, the hybrid tubes were subjected to the quasi-static axial compression test using a universal pressure testing machine with a constant displacement rate of 10 mm/min until their complete crushing, and the specific energy absorption, crushing force efficiency, and crushing mode shapes were extracted for each tube. The results show that in the low thicknesses of the composite layers, filling the tubes with polyurethane foam effectively improves the specific energy absorption and the crushing force efficiency. However, the role of the foam becomes less effective and even negative in the high thicknesses of the composite layers.

Fish cell cellular metastructures have received wide interest from researchers due to their zero Poisson ratio behaviour. However, their production, which is mainly based on additive manufacturing processes, is one of their limitations. Therefore, in this research, a new method based on the conventional manufacturing processes including laser cutting and metal forming was presented for the production of metallic cylindrical metastructures. Two samples were manufactured using this method and their quality was verified using mechanical and non-destructive tests. The samples’ mechanical and buckling behaviour under uniaxial compression were simulated using ABAQUS FEM package and experimentally validated. This was followed by the effects of the metastructures’ geometrical parameters including the cylinder diameter, height and thickness on their linear buckling being investigated numerically, and the results compared with the outcome of classic theories for conventional cylinder buckling. The results showed that these metastructures can be produced successfully with the conventional manufacturing processes, and t the buckling behaviour of these metastructures does not follow the classical buckling theories of cylinders; their buckling behaviour shows much lower sensitivity to the thickness and radius changes in comparison with conventional cylinders.

Roll forming of amorphous PVC based composite laminates were studied in this paper for the first time. For this, [0/90]6 and [45/-45]6 lay-ups of this composite laminates with dimensions of 80×12 cm were fabricated using film stacking and hot pressing processes. The suitable forming temperatures of the composites were determined and then, the laminates were roll formed at 170ᵒC with a single stand and also multi stand roll forming process into channel sections. Geometrical defects including warping, flange waviness and spring back of the roll formed profiles were evaluated. Finally it was concluded that [0/90]6 lay-up results in very lower defects in comparison with [45/-45]6 lay-up, and also the final stand of roll forming process has dominant role on the defects of multi stand roll forming.

Due to the polar functional groups of PVC thermoplastic and its good adhesiveness to the metals, production and roll forming of PVC/ aluminuim/ glass fiber FMLs were investigated in this research. At the first, flexural strength and bonding quality between PVC matrix and aluminuim layer in the FMLs were studied by doing three point bending tests according to ASTM D790 standard. In the following, FMLs with dimension of 12×80 cm and two layups including [0/90, 0/90, Al]s and [45/-45, 45/-45, Al]s were produced using film stacking and hot pressing procedure. The FMLs were rollformed into 30, 45 and 60º channel section profiles at 160ᵒC using a single stand rollforming process and geometrical decects including profile bowing, edge wrinkling, spring back and also aluminuim/composite layers delamination of the resulted profiles were evaluated. The FMLs also were roll formed into 86º channel section profiles using a multi stand roll forming process and the effects of multi stand roll forming on the defects stacking were evaluated. Finally, it was concluded that more than 45º bend angle increase in a rollforming stand results in composite/ aluminum delamination. Also, placement of the reinforcing fibers in the longitudinal direction of the profiles reduces the profile bowing and edge wrinkling defects significantly.

In this paper, the effect of processing temperature on the elastic and viscoelastic properties including storage modulus, loss modulus and damping value of PVC/plain weave fiberglass composites laminates was investigated. For this, composite samples with [0/90]10 lay ups were produced in three different temperatures including 160 ᵒC, 200 ᵒC and 230 ᵒC using film stacking procedure. Firstly, the flexural strength and modulus of the samples were measured using three points bending test according to ASTM D790-07 standard. Then, viscoelastic properties of the samples were measured in the temperature range of 25 ᵒC up to 220 ᵒC using Dynamic Mechanical Thermal Analysis (DMTA) and the effect of temperature on the viscoelastic properties was studied. Also, the effect of fiber/ matrix impregnation quality on the thermal and dynamic properties of the samples was evaluated using optical microscope images. It was concluded that the temperature of 230 ᵒC is proper to achieve high quality impregnation, according to both DMTA and three points bending test. Also, it was seen that increase of processing temperature up to 230 ᵒC increases the storage modulus; however, processing temperature doesn’t affect the glass transition temperature of the samples.

In this research, the machinability of iron-recycled grey cast iron powder metallurgy parts is investigated. For this purpose, grey cast iron swarfs were transformed to powders by target jet milling method and were then used to prepare powder metallurgy parts in combination with commercial iron powder. Green compacts were prepared with the variables of cast iron powder percentage and compaction pressure. Design of experiments was conducted by response surface method for sintered parts with the variables of cast iron powder percentage, compaction pressure, sintering temperature and sintering time each in five levels. Regression analysis and analysis of variance were used to investigate the effect of input parameters, develop the mathematical models and evaluate the validity of the models. In the green section, machinability was qualitatively investigated in drilling. For sintered parts, machinability was evaluated by measuring the thrust and torque forces and the obtained surface finish in drilling. The obtained results certificated the accuracy of the extracted regression equations for predicting the machining properties of the parts. Also, the results demonstrated that the addition of jet milled grey cast iron improves the machinability of iron-based powder metallurgy parts.

In this research، grey cast iron scraps were recycled into powders and were then used in combination with iron powder for producing iron based powder metallurgy parts. Design of experiments was conducted by response surface method for both the green and sintered parts. For the green properties، the parameters cast iron powder percentage and compaction pressure، and for the sintered parts، the mentioned parameters in addition to sintering temperature and sintering time were selected each in five levels as the input process parameters. Transverse rupture strength and elastic modulus were measured as the responses. Regression analysis and analysis of variance were used to investigate the effect of input parameters، develop the mathematical models and evaluate the validity of the models. Scanning electron microscopy and optical microscopy micrographs were provided to better understanding. The obtained results، in addition to determine the effects of the input parameters، demonstrated the adequate mechanical properties of the produced parts in industrial scales and the validity of the proposed models. Also، the proposed method demonstrated its good capability for estimation of elastic modulus of powder metallurgy parts.