FEM SIMULATION OF DEEP DRAWING PROCESS OF ALUMINIUM ALLOYS

This paper presents results of research with FEM simulation of sheet metal forming process. The two types of aluminium alloys from 5XXX and 6XXX series, which are used in automotive industry, were compared. The computer simulation and numerical analysis of deep drawing cup test were used to predict the ability of the forming of these alloys. The plasti-city model Hill'90 was used for stamping simulations. The results of nu-merical simulation were validated by real experiment using sheet metal testing machine Erichsen 145-60. Both results were compared with regard to prediction accuracy in changes of thickness and ear profile

Manufacture of Bead-Stiffened Panels Using the Single Point Incremental Sheet Forming Technique

This paper presents the results of experimental research on the fabrication of thin-walled panels with longitudinal stiffening ribs by the single point incremental sheet forming technique. The bead-stiffened panels were made of Alclad 2024-T3 aluminium alloy sheets commonly used in aircraft structures. The influence of forming parameters and tool strategy on surface quality and the possibility of obtaining stiffening ribs with the required profile and depth was tested through experimental research. Two tool path strategies, spiral with continuous sinking and multi-step z-level contouring, were considered. The results of the experiments were used to verify the finite element-based numerical simulations of the incremental forming process. It was found that the main parameter which influences the formability of test sheets is the tool path strategy; the tool path strategy with multi-step z-level contouring allowed the rib to be formed to a depth of 3.53 mm without risk of cracking. However a greater depth of rib equal of 5.56 mm was achieved with the continuous tool path. The tool path strategy was also the main parameter influencing the surface finish of the drawpiece during the single point incremental forming process

Experimental and Numerical Investigations of Thin-Walled Stringer-Stiffened Panels Welded with RFSSW Technology under Uniaxial Compression

Many aircraft structures are thin walled and stringer-stiffened, and therefore, prone to a loss of stability. This paper deals with accurate and validated stability analysis of the model of aircraft skin under compressive loading. Both experimental and numerical analyzes are conducted. Two different methods of joining panel elements are considered. In the first case, the panel is fabricated using rivets. In the second variant, the refill friction stir spot welding technique is used. Both types of panels are loaded in axial compression in a uniaxial tensile testing machine. The geometrically and physically nonlinear finite element analyzes of the panels were carried out in ABAQUS/Standard. The Digital Image Correlation measurement system ARAMIS has been utilized to monitor the buckling behavior and failure mode in the skin-stringer interface of the stiffened panels. The results of experiments and the digital image correlation system are presented and compared to the numerical simulations

Application of X-ray Diffraction for Residual Stress Analysis in Truncated Cones Made by Incremental Forming

The final accuracy of the parts formed using single point incremental forming greatly depends on the mechanical properties of the material to be formed and the residual stress formation. In this paper, an X-ray diffraction technique was used to study the distribution of the residual stress along the generating line of the conical drawpiece. A DC04 steel sheet with a thickness of 0.8 mm was used as a test material. The basic mechanical properties of the DC04 sheet metal were determined in the uniaxial tensile test according to the EN ISO 6892–1:2016. It was found that the maximum amount of the residual stress existed in a point located in the midway between a base and a truncation of the drawpiece. In the outer surface of the drawpiece, the orange peel defect associated with a rough surface appearance after SPIF a drawpiece, was observed. In contrast, the inner surface of component was characterized by linear grooves associated with the interaction of tool tip with the sheet surface. This defect is mainly influenced by vertical step size

Fatigue Life Assessment of Refill Friction Stir Spot Welded Alclad 7075-T6 Aluminium Alloy Joints

Refill Friction Stir Spot Welding (RFSSW) shows great potential to be a replacement for single-lap joining techniques such as riveting or resistance spot welding used in the aircraft industry. In this paper, the fatigue behaviour of RFSSW single-lap joints is analysed experimentally in lap-shear specimens of Alclad 7075-T6 aluminium alloy with different thicknesses, i.e., 0.8 mm and 1.6 mm. The joints were tested under low-cycle and high-cycle fatigue tests. Detailed observations of the fatigue fracture characteristics were conducted using a scanning electron microscope (SEM) with energy dispersive X-ray spectroscopy (EDS). The locations of fatigue failure across the weld, fatigue crack initiation, and propagation behaviour are discussed on the basis of the SEM analysis. The possibility of predicting the propagation of fatigue cracks in RFSSW joints is verified based on Paris’s law. Two fatigue failure modes are observed at different load levels, including shear fracture mode transverse crack growth at high stress-loading conditions and at low load levels, and destruction of the lower sheet due to stretching as a result of low stress-loading conditions. The analysis of SEM micrographs revealed that the presence of aluminium oxides aggravates the inhomogeneity of the material in the weld nugget around its periphery and is a source of crack nucleation. The results of the fatigue crack growth rate predicted by Paris’s law were in good agreement with the experimental results

Concentration and fluxes of dissolved organic carbon (DOC) in three Norway spruce stands along a climatic gradient in Sweden

Leaching of dissolved organic carbon (DOC) from the forest floor and transport in soil solution into the mineral soil are important for carbon cycling in boreal forest ecosystems. We examined DOC concentrations in bulk deposition, throughfall and in soil solutions collected under the O and B horizons in three Norway spruce stands along a climatic gradient in Sweden. Mean annual temperature for the three sites was 5.5, 3.4 and 1.2 C. At each site we also examined the effect of soil moisture on DOC dynamics along a moisture gradient (dry, mesic and moist plots). To obtain information about the fate of DOC leached from the O horizon into the mineral soil, 14C measurements were made on bulk organic matter and DOC. The concentration and fluxes of DOC in O horizon leachates were highest at the southern site and lowest at the northern. Average DOC concentrations at the southern, central and northern sites were 49, 39 and 30 mg l1, respectively. We suggest that DOC leaching rates from O horizons were related to the net primary production of the ecosystem. Soil temperature probably governed the within-year variation in DOC concentration in O horizon leachates, but the peak in DOC was delayed relative to that of temperature, probably due to sorption processes. Neither soil moisture regime (dry, mesic or moist plots) nor seasonal variation in soil moisture seemed to be of any significance for the concentration of DOC leached from the O horizon. The 14C measurements showed that DOC in soil solution collected below the B horizon was derived mainly from the B horizon itself, rather than from the O horizon, indicating a substantial exchange (sorption–desorption reactions) between incoming DOC and soil organic carbon in the mineral soil