Ojačanje spojeva između LVL elemenata polimerima ojačanim staklenim vlaknima i analiza metodom konačnih elemenata

The goal of this study was to investigate the effect of glass fiber reinforced polymer (GFRP) on joints made of laminated veneer lumber (LVL), through experimental data and evaluation by ANSYS finite element (FE) software. In order to fabricate LVL, veneer from poplar (Populus deltoides Bartr. ex Marsh) with 2.5 mm thickness and PVA adhesive were used. T-shape joints out of LVL were made and two wooden dowels were incorporated as well. Then GFRP was applied to reinforce the joints. GFRP in three grammages (100, 200 and 300 g/ m2) was adhered to joints with epoxy resin. Joints reinforcement was performed by a two-layer reinforcing agent. For comparing the effectiveness, half of the specimens were reinforced on sides and the other half on edges. Specimens were tested in static bending. The results have shown that GFRP had a significant effect on the strength of joints. Reinforced joints on both sides were stronger than those reinforced on edge. Joints reinforced with 300 g/m2 GFRP were improved by 35 % and 43 %, respectively, compared to 100 and 200 g/m2 grammage. Failure modes of specimens are dependent on GFRP grammage. The results of FE have shown that the highest concentration of stress and elastic strain was generated in the tension and compression zones of joints.Cilj rada bio je na temelju eksperimentalnih podataka i analize konačnih elemenata (FE) te uz pomoć softvera ANSYS istražiti utjecaj polimera ojačanog staklenim vlaknima (GFRP) na spojeve od lamelirane drvne građe (LVL). Za izradu LVL-a upotrijebljen je furnir drva topole (Populus deltoides Bartr. ex Marsh) debljine 2,5 mm i PVA ljepilo. Izrađeni su T-spojevi od LVL-a i ugrađena su dva drvena moždanika. Zatim je za ojačanje spojeva primijenjen GFRP u tri gramature (100, 200 i 300 g/m2) tako da je epoksidnom smolom zalijepljen na spojeve. Ojačanje spojeva izvedeno je dvoslojnim armaturnim sredstvom. Radi usporedbe učinkovitosti, polovica uzoraka ojačana je sa strane, a druga polovica na rubovima. Uzorci su ispitani na statičko savijanje. Rezultati su pokazali da GFRP ima značajan utjecaj na čvrstoću spojeva. Spojevi ojačani s obje strane bili su jači od onih ojačanih na rubu. Spojevi ojačani GFRP-om od 300 g/m2 poboljšani su za 35 % odnosno za 43 % u usporedbi s GFRP-om gramature100 i 200 g/m2. Načini loma uzoraka ovisili su o gramaturi GFRP-a. Rezultati analize konačnih elemenata pokazali su da se najveća koncentracija naprezanja i elastične deformacije pojavljuje u vlačnoj i tlačnoj zoni spojeva

Mechanical characterization of integral aluminum-FRP-structures produced by high pressure die-casting

Due to the growing demand for light-weight solutions in a wide range of industrial sectors, the selection and combination of different materials is becoming more and more important. As a result, there is an increasing need for suitable joining technologies. In a new joining process, flexible glass fiber textiles are integrated into aluminum by high pressure die casting in the first production step. These structures are used for the electrochemical insulation between aluminum and carbon fiber textiles, which are connected in the subsequent production step by textile technology. The finished compound is formed in a final resin impregnation process. Challenges faced by Fraunhofer IFAM lie in the positioning, pre-tensioning, and infiltration of the glass fiber textiles in the high pressure die-casting process. The advantage of this joining technology, in addition to the electrochemical insulation between aluminum and carbon fibers, is in a slim and light-weight connection. Therefore, no thickening of the individual joining partners is necessary, and the force flow lines are not deflected. Within mechanical investigations of those hybrid structures it was determined, that the infiltration content of aluminum has only a small influence on the achievable tensile strength. Rather, casting parameters such as the holding pressure have an influence. The subsequent resin infusion process enables an additional infiltration by the resin system of fiber bundles that have been only slightly infiltrated with aluminum. As a result, additional adhesion can be achieved and the infiltration gaps can be closed. Furthermore, an influence on the achievable tensile strength was observed regarding the use of the fiber material. Further increases in tensile strengths were also observed by adapting the textile parameters (e.g. reduction of the fiber undulations). A variety of failure behaviors could be observed in dependence on textile and process parameters. Tensile strength of the hybrid structures was compared to reference samples made of glass fiber reinforced epoxy resin, to determine the loss of strength caused by the joining technology. Further investigations were carried out, including a fracture surface analysis using a scanning electron microscope. Thus it was possible to determine mechanisms of adhesion between encapsulated glass fibers and the surrounding aluminum matrix