Moisture Effects on the Mechanical Behavior of Fir Wood Flour/Glass Reinforced Epoxy Composite

Fir wood flour may be used as filler in glass reinforced composites due to the lower content of tannins in comparison with oak wood flour (Cerbu et al. 2010). This work focuses on the behavior of E-glass / fir wood flour / epoxy hybrid composites in mechanical tests (three-point bending tests, and Charpy impact tests) after immersion in water for 1177, 3048, and 6572 hours. Alternating layers were reinforced either with glass fabric or with fir wood flour. After 3048 hours of immersion, the flexural properties decreased: the modulus of elasticity (MOE) in bending and maximum flexural stress σ decreased by 13.16% and 37.54% respectively, with respect to the values recorded in the case of the dried specimens. The properties recovered a little after saturation because they increased after 6572 hours of immersion: MOE was greater (4.36%), while maximum flexural stress was greater (6.78%) with respect to the values corresponding to the specimens tested after 3048 hours of immersion. In the Charpy test, the impact strength K was measured. The damage (cracks developed at matrix-glass interface) caused by water absorption is discussed in order to explain the degradation of the mechanical properties. The adding of the wood flour led to the increasing of the modulus of rigidity EI in bending and it is proved by comparing with the results obtained in case of glass / epoxy composite without wood flour. Components for outdoor furniture (gardens) could be an application of the hybrid composite analyzed in this paper

Practical solution for improving the mechanical behaviour of the composite materials reinforced with flax woven fabric

This article focuses on finding a practical solution for improving the mechanical behaviour especially in bending in case of the composite materials reinforced with flax fabric. For this purpose, two kinds of composites having the same number of layers are mechanically tested: the flax/epoxy composite and the flax/glass/epoxy composite (hybrid composite). The mechanical tests used were tensile test and bending test (three-point method). Different results corresponding to the weft or warp directions were remarked in case of the hybrid composite: for example, the maximum values of the tensile strength and the flexural strength measured in the weft direction are 40.63% and 34.61% greater, respectively, than the values corresponding to the warp direction. This article reports the improvement of the mechanical properties by replacing the flax reinforcement with glass reinforcement in the two upper and lower layers of the flax composite materials: increasing with 35.19% in terms of Young’s modulus E recorded in the tensile test, with 79.86% of the maximum value of the tensile stress and with 91.08% of the maximum value of the flexural stress. Composite beam theory was considered and theoretical approaches were validated by the experimental results

Effect of the Looseness of the Beam End Connection Used for the Pallet Racking Storage Systems, on the Mechanical Behavior of the Bearing Beams

The worldwide use of pallet racking storage systems leads to the necessity for research regarding the effects of the clearance between the metallic tabs of the connector and upright slots (looseness effect) on the performance of load-bearing beams. Firstly, the looseness angle and the rotational stiffness were experimentally obtained for three types of beam-to-upright connections. A theoretical approach is used to investigate the magnitude of the looseness effects that occurred on the performances of the bearing beam of the pallet storage systems in terms of the bending moment developed at the midpoint of the beam and maximum deflection. Calculation corrections were evaluated for the connections involved in the experimental part, for the case which considers the looseness effects with respect to the case which does not consider the looseness effect. In order to evaluate the effects of the parameters of the connections on calculus corrections, the theoretical model was used for other types of beam-to-upright connections. It is shown that the maximum corrections are 2.99% and 5.16% for the bending moment developed at the midpoint of the beam and for the maximum deflection, respectively. It is proved that the connector type affects the size of the correction

A Method for Reducing of the Overall Torsion for Reinforced Concrete Multi-Storey Irregular Structures

The uneven distributions of mass and stiffness in the case of multi-storey concrete buildings lead to a torsion sensitivity of those civil structures under dynamical loadings like earthquakes or wind and gusts. In order to minimize the overall torsion, it is imperatively necessary to reduce the distance between the centre of mass (CM) and centre of stiffness (CS) in the design stage. In this context, the main purpose of this paper is to present a theoretical method of reducing torsion by minimizing the distance between CM and CS at the level of each floor of the structure. Principal stiffness axes are also changed in convenient directions so that the movement of the structure leads to a favourable plastic mechanism in the fundamental mode of vibration. To achieve the goal, the main objective is to change the dimensions and orientations of the pillars located on the perimeter of the structures. The described method was used to study: irregular shaped structures in plan; structures with stairs or with central concrete core; structures with elevation retractions. The overall torsion reducing was achieved with Matlab programs, and the verification of the results was carried out by using the software ETABS 2016