Composite Materals

Birdstrike on aircraft is a major threat to human life and there is a need to develop structures which have high resistance towards birdstrike. This paper describes the numerical simulation of bird strike on the Aluminium Silicon Carbide (Al-SiC) metal matrix composite wing leading edge using LS-Dyna software. The metal matrix composite chosen has the composition of Aluminium 85% and Silicon Carbide 15%. At this composition the impact force of the material is high which means the material is more resistant to impacts which is suitable for the wing leading edge as it is subjected to events like birdstrike. For this simulation we have chosen the wing structure of Boeing 737 aircraft. The wing leading-edge section was designed using CATIA V5 with skin thickness of 2mm. Also, the ribs and the spar were designed for better results. A hemisphere cylindrical bird model is used for bird strike and is designed in LS Pre-Post V4.7.7 with length 196mm and diameter 98mm. The wing leading edge model was imported to the LS Pre-Post and was aligned properly for birdstrike analysis. The analysis of the birdstrike is carried out using the Lagrangian method. The required keyword input data such as Boundary Definition, Control, Contact Definition, Material properties for the bird and the wing leading edge section and Velocity for the bird are defined as per the requirements of the analysis. The simulation was run at different velocities ranging from 50-150m/s. The results were obtained graphically as Pressure vs. Time, Effective Stress vs. Time, Effective Plastic Strain vs. Time, Rigid Body Displacement vs. Time, Internal Energy vs. Time and Kinetic Energy vs. Time graphs. Using these graphs, the graphs for the Effective Stress vs. Effective Plastic Strain & Rigid Body Displacement vs. Velocity were plotted. In this analysis, it was observed that the Effective Stress of the wing leading edge with Al-SiC material has been increased by approximately 100 MPa with respect to the traditional Al 7075 T6 material. Also, the pressure distribution over the wing leading edge surface is smoother during impact for wing section with Al-SiC material. The energy absorption of the wing section has been increased. The overall strength of the wing leading edge section with Al-SiC as the material has been increased when compared to the wing leading edge section with Al 7075 T6 material.

Sandwich structures with face sheets made of carbon fiber reinforced plastics (CFRP) demonstrate a high potential to reduce both production costs and the weight of primary aircraft structures. This potential has however yet not been realized mainly due to the complex structural and material behavior of sandwich structures under different kinds of loading and adverse effects like moisture take up of honeycomb core material [1]. Using closed cell hard foams such as PMI foam, better known as Rohacell®, the issue of moisture take-up has been solved. One more critical issue however is the often criticized lack of damage tolerance of sandwich structures [2].
Impact damage resistance is part of the larger topic of damage tolerance. It can be treated separately as impacts may cause a damage that is used a starting point for a damage tolerance analysis while not vice versa. In consequence the resulting damage size of a predefined impact scenario is of great importance.

The paper presents tribological behaviour of hybrid aluminium composite A356/10SiC/3Gr in dry-sliding conditions. Hybrid
composites were made with a modified compocasting procedure and tribological tests were conducted on a tribometer with a
block-on-disc contact geometry. An analysis of the effects of three sliding speeds ((0.25, 0.5 and 1) m/s) and two normal loads (10 N and 20 N) on the wear volume and wear rate was conducted for different sliding distances. The total sliding distance was
300 m. SEM and an EDS analysis of the wear surfaces of the tested material were also performed. The analysis of the wear
surfaces shows an intensive adhesive wear of hybrid composites. Also, the appearance of mechanically mixed layers (MMLs) was confirmed, i.e., an increase in the concentration of iron in the hybrid composite material.

In present study, the tribological behavior of hybrid
composites with A356 aluminum alloy matrix reinforced with 10 wt% of SiC and 3 wt% of graphite was investigated using the Taguchi method. The composites were produced by the
compocasting procedure. The tribological properties were studied using block-on-disk tribometer under unlubricated sliding conditions at different normal loads (40N, 80N and
120N), sliding speeds (0.25 m/s, 0.5 m/s and 1 m/s) and sliding distances (150 m, 300 m and 1200 m). Analysis of the wear rate results was performed using the ANOVA technique. The
highest influence on wear rate was obtained for sliding distance (39.44%). The influence of normal load and sliding speed was 27.96% and 14.12%, respectively. The lowest level of wear rate corresponded to the contact conditions with normal load of 40N, sliding speed of 1.0 m/s and sliding distance of 1200 m.

Sandwich structures with  face sheets made of carbon fibre reinforced plastics  (CFRP) have a high potential in  reducing production costs and  weight of primary  aircraft structures. Their  advantage is based on their superior bending stiffness compared to solid laminates. This allows a less complex and highly integrated structural design which typically reduces the number of parts and joints significantly. The highlighted potential has however yet not been realized within primary aircraft structures mainly due to the complex structural behaviour. Another adverse effect often mentioned is moisture take up of the core material. Using closed cell hard foams such as PMI foam, better known as Rohacell®, for the core, the problem of moisture take-up has been solved. Damage tolerance however has been one of  the most critical  issues regarding the  use of sandwich structures [1]  [2]. Extensive research has been conducted on CFRP foam core sandwich structures with mostly PVC foam for application in marine vessels, which provides a large benefit for today’s level of understanding. Past and current research  concentrates on describing material behaviour with damage, damage growth under cyclic loading  and consequently  maximum  damage  sizes [3]-[5]. Less attention  has however  been given to damage initiation by localized impact events. Low Velocity impact may lead to face sheet
and/or core damages [6]-[8].

The rheological properties of fresh plaster mortars, with varied contents of porous fillers and polymer admixtures, have been studied. The quantities of fine limestone and expanded perlite, and dosages of methyl hydroxy ethyl cellulose and ethylene vinyl acetate were varied in the experiment. Effective viscosity (at a shear rate from 0.045 to 5.705 s−1) and the thixotropy of the mixes were determined with rotational viscometer for 18 compositions (according to the design of the experiment). Each of the 18 viscosity curves were described with the Ostwald–de-Waele equation. The Experimental–Statistical models describing the dependencies of the parameters of the rheological model and of mix thixotropy on the composition factors were built on the obtained data. ES-models have allowed the individual and synergetic effects of mix components on the rheological characteristics to be evaluated. The expanded perlite powder can increase the viscosity by two times, probably due to its pozzolani...