A generally laminated composite beam with a solid rectangular cross-section of doubly symmetrical cross sections, as shown in Figure 1, is considered to be studied. In the analytical models, the flexural-torsional coupling effects are ignored and pure torsional vibrations are taken. Also, analytical models are developed by classical lamination theory and shear deformation theory to study the torsional vibrations of the beams. Mindlin eight-node isoparametric layered shell elements (SHELL 99) are employed in the modeling for describing the torsional vibrations of these beams.
1. Impact Behavior
The torsional frequency for clamped-simply supported condition comes to be lower than clamped-clamped condition, then simply supported-simply supported comes to be lower than clamped-simply supported, and finally clamped-free condition comes to be lower than other supports. The influence of boundary conditions on torsional natural frequencies is investigated for the 1st torsional frequency as shown in Figure 6. The analysis can be applied to the laminated beam previously mentioned with the same dimensions and geometry. They are deduced by FEM ANSYS for the first six torsional frequencies.
The Influence of Ply Stacking Sequence on Mechanical Properties of Carbon/Epoxy Composite Laminates
A modal analysis will be carried out using ANSYS 10.0 finite element software to study the frequencies of free torsional vibrations of the mentioned composite laminated beam. In the present study, the torsional vibration behaviors of symmetrical laminated composite beams are studied. Yõldõrõm and Kõral studied the out-of-plane free vibration problem of symmetric cross-ply laminated beams using the transfer matrix method. With these requirements, this work considers the free torsional vibrations for laminated composite beams of doubly symmetrical cross sections. Finding free torsional vibrations characteristics of laminated composite beams is one of the bases for designing and modeling of industrial products. The bending mismatch coefficient between two adjacent laminates, different fibre orientations, and stacking sequences between the layers causes delamination; the delamination area increases as the mismatch coefficient increases .
1. Flexural Properties
- At 5, 10, and 15 J impact energy, the laminates exhibited a rebound effect after the impactor contact force reached the peak force zone.
- Hybrid fibre-reinforced composites comprise at least one pair of two different fibres combined in a solitary polymer matrix, resulting in improved properties compared to a normal polymer composite.
- The leaf produces a lot of cellulose fibre, with cellulose making up the majority (70–82%) and lignin (5–12%) and ash making up the remainder (1.1%) .
- Consequently, a laminate with varied ply orientations limits energy transfer over its thickness and fails when subjected to higher loads .
- This possibility makes once more these materials very attractive since it makes possible to obtain the desired torsional natural frequencies without increasing mass or changing geometry.
- When the impact energy is delivered at a low level, the computations demonstrate that quasi-isotropic laminates absorb less energy than the cross- and angle-ply laminates.
- Consequently, the effects of the glass/natural fibre-reinforcement stacking sequence were also examined in various hybrid formulations with GFRP 30,31,32.
The commercial finite element program ANSYS 10.0 is used to perform a dynamic modelling to the laminated beams by performing an eigenvalue analysis. Evangelos and Sapountzakis studied the Torsional vibrations of composite bars by (BEM) boundary element method which is developed for the nonuniform torsional vibration problem of doubly symmetric composite bars of arbitrary constant cross-section. Kameswara and Mirza studied the problem of free torsional vibration and buckling of doubly symmetric thin-walled beams of open section, subjected to an axial compressive static load and resting on continuous elastic foundation. Studied the torsional vibration of open and variable cross section bars by derive analytical method is to form the dynamic stiffness matrix of the bar, including the effect of warping. Exact torsional vibration frequencies were presented by for the case of circular cross-section shafts subjected to classical boundary conditions avoiding in this way warping effects. Several researchers have dealt with torsional vibration of beams.
Table 1. Material elastic properties
- Further research is required to study the compression and shear properties, which can play a vital role in further analysing the internal and interface failure of the laminates.
- The difference between them was that the PPPP-untreated laminate was penetrated at 12.5 J, whereas the PPPP-treated laminate was penetrated at 17.5 J.
- The laminates were manufactured using a vacuum infusion approach with various stacking sequences and ply orientations classified as symmetric quasi-isotropic, angle-ply symmetric, and cross-ply symmetric.
- On the other hand, LM2 exhibited high interlayer delamination between 0°/90° stacking configuration, as revealed in Figure 6.
- Through visual inspection, delamination was observed to occur at the interfaces of different stacking sequences and ply orientations.
- This observation was in agreement with previous studies on the response to the impact of sisal/epoxy composites .
- The practical significance of this study is to provide structural engineers with a better understanding of how the ply stacking pattern of the laminates can be tailored to strengthen structural reinforcement.
This behaviour could result from a random distribution of carbon fibres across the plies since the lamina geometry above and below the midplane are identical 35,36. Average flexural and tensile properties of the CFRP with different stacking sequences. However, one notable observation in this case (Figure 3a) is that the laminate spontaneous catastrophic failure occurred immediately after the maximum load was attained due to fibre breakage. Subsequently, the laminates experience a sudden drop in load due to failure within the internal plies, followed by continuous stress fluctuations at an increasing deformation rate. Five specimens per laminate with dimensions of 75 mm ×10 mm×3.5 (±0.1) mm, as shown in Figure 2c, were also tested on a Zwick Roell HIT25P pendulum impact tester with a working capacity of 7.50 J following the ASTM D6110 recommendation.
Figure 14.
The CPPC laminate at ±45°2,0°/90°2s ply orientations demonstrated the maximum absorbed energy when it was subjected to the highest impact energy in which almost the entire impact energy was absorbed. Although they could sustain a higher impact, all laminates absorbed less impact energy than the laminates at 0°/90°8 ply orientation, particularly the pure PALF laminate. The energy profiling diagram of the hybrid laminates at a ply orientation of ±45°8 is illustrated in Figure 15b. Figure 15a shows the energy profiling diagram of the hybrid laminates at a ply orientation of 0°/90°8. Figure 6, Figure 7 and Figure 8 illustrate the impact behaviour of the hybrid laminates at a ply orientation of ±45°8. In order to comprehensively understand the behaviour of the composites after impact, the interplay between ply orientation and stacking sequences is required.
Ply orientation is important in designing composite laminates to withstand high-impact loads. The laminates with an exterior carbon layer can withstand high impact energy levels up to 27.5 J. The laminates were manufactured using a vacuum infusion approach with various stacking sequences and ply orientations classified as symmetric quasi-isotropic, angle-ply symmetric, and cross-ply symmetric. The finite element software package ANSYS is an efficient vibration prediction tool, because of its ability to model the laminated composite beam and reveal fundamental modal frequencies and modal shapes. This study is the first attempt to deal with the torsional natural frequencies of laminated composite beam with different lamination.
Table 5.
Contact force–displacement of the hybrid laminates at ply orientations of 0°/90°2, ±45°2s. The laminates with ply orientations of ±45°n, 0°/90°ns exhibited force–displacement curves that revealed mixed tendencies. However, this phenomenon exhibited by the PPPP-untreated and PPPP-treated laminates, which oriented at 0°, 90°8, produced higher tensile strength compared to laminates with ±45°8 ply orientation .
During this stage, indentations and damages were observed in the impact queenwin casino review area of the top exterior carbon layer. The fracture of the laminate was initiated from the top exterior carbon layer, as shown by the contact force reaching the peak value. In comparison to Figure 5, the PPPP-untreated and PPPP-treated were stiffer at ±45°8 ply orientation compared to 0°, 90°8. The CPPC laminate exhibited a similar rebound curve trend up to the maximum contact force. The stiffness values of the PPPP-untreated and PPPP-treated samples were significantly different, at which PPPP-treated were able to almost withstand 20% more impact content force.