Ply Configuration Research Articles

Eliminating cracks in Ti–47Al–2Cr–2Nb/Ti–6Al–4V micro-laminated composites fabricated by dual-material laser powder bed fusion

The low ductility of titanium aluminide at room temperature has been one of the factors that severely limit its applications. In this study, Ti–6Al–4V (Ti64) alloys were combined with Ti–47Al–2Cr–2Nb (TiAl) alloys to make micro-laminated composites with optimal ply configurations to eliminate crack formation in TiAl and improve the ductility. A dual-material laser powder bed fusion (LPBF) system was used to fabricate the TiAl/Ti64 micro-laminate samples. The presence of cracks, elemental composition and mechanical properties were experimentally characterised and analysed to understand the effect of ply configuration and the mechanism of eliminating cracks. It was found that smaller TiAl ply thickness and lower TiAl volume fraction result in fewer cracks formed in the micro-laminates. Elemental composition analysis reveals that the Al content in the first two powder layers (i.e., 200 μm thick in total) of a TiAl ply is reduced to 10%–35% due to the partial mixture of the TiAl ply and the proceeding Ti64 ply in the LPBF. The reduced Al content leads to combined α-Ti, β-Ti and α2-Ti3Al phases instead of γ-TiAl phases, thus eliminating the formation of cracks within the first 200 μm thick region of the TiAl ply. This study demonstrates that crack-free and dense TiAl/Ti6 micro-laminated composites can be produced with the TiAl ply thickness reduced to 200 μm and the TiAl volume fraction reduced to 25% (Ti64 ply thickness 400 μm). Ductility of the crack-free micro-laminates at room temperature is comparable to or even exceeds the properties of TiAl/Ti64-type laminates made by other manufacturing processes, which may imply good machinability. Note that further research is required to investigate the properties and applications of the micro-laminates at elevated temperatures.

In search of the quasi-isotropic laminate with optimal delamination resistance under off-axis loads

Delamination is one of the most feared failure modes in laminated composites and yet there is a lack of well established procedures to find the ply configuration with the highest delamination resistance for a given geometry of the component and a set of elastic and strength constraints. This paper presents a methodology for determining the quasi-isotropic ply sequence more resistant to delamination under off-axis uniaxial tension. Delamination is considered to be triggered by interlaminar stresses at free-edges or by matrix cracks. Two different ply thicknesses (standard and thin) and two sets of ply orientations (multiples of π/4 or π/8) are considered. The results show that the use of thin plies enlarges the design domain by up to 70% and generates a practically isotropic safe space. The methodology presented is also suitable for optimizing the delamination resistance of other load cases with stress singularities.

A new technique to measure shear fracture toughness of adhesives using tensile load

The end notched flexure (ENF) test is the most common method for measuring the mode II fracture energy of adhesives which provides reliable results but has some inherent problems. The shear fracture energy calculated using ENF for brittle adhesives is often based on a single data point (corresponding to the fracture load) obtained from the test where the crack grows catastrophically and the results are significantly sensitive to pre-crack tip conditions. The aim of the current study is to introduce a new pure mode II fracture test suitable for measuring the shear fracture energy of adhesives. A new technique for measuring the mode II critical strain energy release rate (SERR) of brittle adhesives is proposed based on the central cut ply (CCP) configuration. Fracture tests were carried out on adhesively bonded steel CCP specimens. It is shown that the crack growth in CCP joints is more stable, and the failure develops in multiple steps that generates more experimental data point during the crack propagation. The mode II fracture energy of a brittle epoxy-based adhesive is extracted using CCP method and is compared with the shear fracture energy obtained from the ENF tests. The effect of adhesive thickness on the obtained fracture energies is also analyzed. The CCP technique can be used to find both the crack initiation and crack propagation toughness values whereas the ENF method only provides the crack initiation fracture energy.

Nonlinear buckling analysis of a sandwich composite semi-ellipsoidal shell under hydrostatic pressure: A numerical and experimental investigation

In this study, nonlinear buckling response of composite sandwich semi-ellipsoidal shell subjected to uniform hydrostatic external pressure is investigated numerically and experimentally. The face sheet of the sandwich shell is made up of laminated composite layers and the honeycomb core is considered as reinforced with and without strips. The various honeycomb core configurations with strip reinforcements are employed in the sandwich semi-ellipsoidal shell. The numerical buckling analysis of the sandwich shell is performed using the commercially available software ANSYS®. The geometric nonlinearity and material nonlinearity of the shell structures are included through the arc length method while solving the nonlinear differential equations and identifying the critical pressure of the structure. The efficacy of the numerical modeling and analysis are verified by comparing the critical pressure obtained through the experimental investigations performed on a composite semi-ellipsoidal sandwich shell and results available in the literature. The various parametric investigations are performed on the composite sandwich shell to study the effect of honeycomb configurations, ply orientation of face sheets, aspect ratio and slenderness of the structure, geometric imperfections on the critical pressure. It was seen that the semi-ellipsoidal sandwich shell having double strip reinforcement core yields higher critical pressure among the various configurations of honeycomb cores. However, the semi-ellipsoidal sandwich shell with the single strip reinforcement in between the core having [0°]6s face sheet composite ply configuration yields higher stiffness to weight ratio which leads to the highest critical pressure among the various configurations of sandwich shell.

Numerical and Experimental Investigations on Nonlinear Buckling Response of a Laminated Composite Shell

In this study, a laminated composite shell with uniformly applied hydrostatic pressure on its external surface is investigated numerically and experimentally. A numerical buckling analysis is carried out on a laminated composite shell with various nonlinearities including geometrical nonlinearity, material nonlinearity and geometric imperfection to obtain the critical buckling pressure using the commercially available software ANSYSⓇ. The eigen mode shape imperfection in the geometry is considered for the nonlinear buckling analysis of composite shell. The force-induced inward dimple (FID) and eigen affine imperfections are also considered for the numerical analysis. The nonlinear governing differential equations of the buckling performance of the shell are solved using the arc-length method coupled with nonlinear finite element analysis. The developed nonlinear finite element modeling of the composite shell is validated by comparing the critical buckling pressures available in the literature obtained for the composite cylinder and prolate and oblate composite domes. Further, the effectiveness of the developed numerical modeling and analysis is demonstrated by performing an experimental investigation on a prototype shell made up of GFRP composites and subjected to external hydrostatic pressure. Various parametric studies are also performed to study the effect of aspect ratio of the shell and ply configuration of the composite shell. It was shown that the buckling pressure of the composite shell is decreased if the FIDs are located at the apex of the shell and eigen affine imperfection amplitude of the shell is increased. However, a substantial effect in the critical pressure of the composite shell could not be observed, if the position of FIDs is located towards the bottom of the shell. It is also found that the composite shell with all 90° ply orientation having aspect ratio of 0.5 yields higher critical buckling pressure.

Prediction of influences of size and locations of delamination on dynamic characteristics of laminated composite plate using particle swarm optimization and artificial neural network

AbstractIn laminated composite structures, delamination is one of the most common defects. The delamination affects the vibration characteristics of laminates, and thus these indicators can be used to detect the potentially catastrophic failures and measures the health characteristics of laminates. In this study, particle swarm optimization (PSO) and artificial neural network (ANN) are used to optimize and predict the influences of location and size of delamination on the dynamic behavior of composite plates. The classical laminated plate theory adopted principle equation based on the dynamic characteristics of composite laminate has expressed through the finite element method. The delamination behavior of laminate composite plate is modeled by considering delamination at several interfaces with variable sizes and locations. PSO methodology is recommended to optimize the decrease in natural frequency due to the delamination with varying weight fractions under completely clamped edge boundary conditions. Further, an ANN algorithm is proposed for predicting the dynamic responses of the composite plate by considering unknown ranges of parameters such as weight fraction, ply configuration, and different delamination locations.

Prediction of influences of MWCNT fillers on the vibration characteristics of laminated hybrid honeycomb core sandwich GFRP composite plate

In this paper, the prediction of influences of multi-wall carbon nanotubes (MWCNT) fillers on the vibration characteristics of laminated hybrid honeycomb core sandwich GFRP composite plate has been performed based on the higher-order shear deformation theory using finite element formulations. The parametric study on the dynamic behavior of honeycomb sandwich composite plates hybrid with MWCNT with the influence of the weight percentage of CNTs for core material and upper and bottom skins with CCCC boundary conditions, different ply configuration was performed. The numerical study clearly shows that the bending frequency increase with an increase in the weight percentage of MWCNTs. It can be observed that the influence of MWCNT in the core is least contributing to increasing the stiffness with the influence of MWCNT in the skins on the bending characteristics. Finally, the ANN technique is used to predict effectively the dynamic characteristics of honeycomb sandwich composite plates hybrid with MWCNT with the influence of intermittent the weight percentage of CNTs for core material and upper and bottom skins which reduces the computational effort.

Influence of ply configuration and adhesive type on cross-laminated timber in flexure at elevated temperatures

This paper describes experiments on cross-laminated timber (CLT) beams exposed to uniform non-charring temperatures under sustained loading. Two different ply configurations and two different adhesive types were examined under sustained loads of both 30 and 50% of the ultimate ambient temperature flexural capacity. It was found that the adhesive type has a significant influence on the magnitude of the deterioration in structural stiffness during heating. From image correlation analysis this influence was attributed to increased shear strains along the adhesive lines between timber plies for specimens bonded with a polyurethane (PU) adhesive, when compared to those that used a melamine urea formaldehyde (MF) adhesive. It was also found that considerable deflections that were measured during heating were irrecoverable during cooling of the CLT, suggesting that these deformations were driven by creep of the timber – and possibly also the adhesives.

Abrasive Wear Performance of Jute–Glass–Carbon-Reinforced Composites: Effect of Stacking Sequence and Fibers Relative Amounts

ABSTRACT In the present study, water absorption and its subsequent effect on abrasive wear performance of jute–glass–carbon-reinforced composites have been investigated. Nine laminates were fabricated in inter–ply configuration with hand lay–up technique. To evaluate water absorption effect, the prepared composite specimens were immersed in distilled water for 60 days. The effects of the reinforcement hybridization, fibers relative amounts, and stacking sequence on abrasive wear performance for aged and un-aged specimens were investigated using a pin-on-disk wear tester at different normal loads and sliding times. Results indicated that hybridizing glass-reinforced composite with jute and/or carbon fabrics improves the wear resistance of the resulting composite. Stacking sequence has a slight effect on wear resistance whilst fibers relative amounts have a visible effect. Water uptake induces a noticeable decrease in the wear resistance of the studied composites. With increasing the applied normal load and the sliding time, the wear resistance of the composites decreases. SEM observations for worn surfaces display fiber-matrix debonding, multiple cracks, fiber fracture, fiber pull out, debris formation and wear scars.

Analytical Analysis of Distribution of Bending Stresses in Layers of Plywood with Numerical Verification

The study presents methods for accurate estimation of bending stresses in the 3-point flexural bending test of plywood, i.e. a wood-based laminate with an alternate crosswise ply configuration. The characteristic bending strength (MOR) and mean modulus of elasticity (MOE) of standard beech plywood was determined using European Standard bending tests EN 310. Correlations were determined between empirically determined bending moduli of the plywood and material moduli of the veneer layer. Calculations were conducted based on the classical plate theory for thin panels comprising the theory of elasticity including the Kirchhoff-Love hypothesis. Rigidity of individual layer was established theoretically in the axial configuration of transformed rigidity matrix values. Numerical laminate models were developed and simulation tests were conducted. Results of experimental and analytical studies were verified using the Finite Element Method (FEM). Analyses were performed in two plywood cross-band arrangement variants. An analysis of the distribution of stresses in individual layers of plywood used an analytical and numerical method assuming the plywood specimen to be a rhombic-anisotropic material. It was found that the bending load capacity of plywood depends on the configuration of individual layers (veneers). Values of stresses originating from bending do not only depend on the distance of the considered plywood layer from the middle layer but also on stiffness in the direction of operating stresses. Bending strength varies in individual directions of the plywood panel. Therefore, the distribution of stresses in individual layers differs from that resulting from the stress distribution for homogeneous isotropic materials. Results are presented in the form of tables, bitmaps, graphs and photographs. The tests were conducted based on the BFU-BU-18 standard beech plywood thickness of 18 mm.

Investigation of Flexural Properties of Glass-Kevlar Hybrid Composite

Composite materials are attracting huge attention due to their superior properties and being inert to most atmospheric effects. They have high strength to weight ratio and can be moulded into the required shape that can be used for various applications as replacement for metals. This paper consists of study of flexural behaviour of hybrid composite reinforced with woven glass fiber and Kevlar fiber in ply configuration. The three point bending test according to ASTM 790 was performed experimentally on this composite laminate. The fiber volume fraction to matrix volume fraction was taken 40%-60%. The volume fraction of the individual fibers in the composite was varied to determine the effects on the flexural strength of the composite laminate. The laminates prepared were having dimension 80mm X 13mm X 3mm. After testing the H4 configuration had the highest flexural strength of 217.91 MPa also the H2 configuration had maximum flexural modulus. The result of the study can be used for the development of actual composites and simulation purpose.

Investigation of Flexural Properties of Glass-Kevlar Hybrid Composite

Composite materials are attracting huge attention due to their superior properties and being inert to most atmospheric effects. They have high strength to weight ratio and can be moulded into the required shape that can be used for various applications as replacement for metals. This paper consists of study of flexural behaviour of hybrid composite reinforced with woven glass fiber and Kevlar fiber in ply configuration. The three point bending test according to ASTM 790 was performed experimentally on this composite laminate. The fiber volume fraction to matrix volume fraction was taken 40%-60%. The volume fraction of the individual fibers in the composite was varied to determine the effects on the flexural strength of the composite laminate. The laminates prepared were having dimension 80mm X 13mm X 3mm. After testing the H4 configuration had the highest flexural strength of 217.91 MPa also the H2 configuration had maximum flexural modulus. The result of the study can be used for the development of actual composites and simulation purpose.

Dynamics of a generally layered composite beam with single delamination based on the shear deformation theory

AbstractThe free vibration analysis of generally laminated composite beam (LCB) with a delamination is presented using the finite element method (FEM). The effect of material couplings (bending-tension, bending-twist, and tension-twist couplings) with the effects of shear deformation, rotary inertia, and Poisson’s effect are taken into account. To verify the validity and the accuracy of this study, the numerical solutions are presented and compared with the results from available references and very good agreement observed. Furthermore, the effects of some parameters such as slenderness ratio, the rotary inertia, the shear deformation, material anisotropy, ply configuration, and delamination parameters on the natural frequency of the delaminated beam are examined.

Damage resistance of aluminum core honeycomb sandwich panels with carbon/epoxy face sheets

The damage resistance of composite sandwich structures with eight and 16 ply quasi-isotropic, carbon/epoxy face sheets and aluminum honeycomb core is evaluated. The external damage is induced quasi-statically, using spherical steel indentors under displacement control, to be in the vicinity of the barely visible threshold. In addition to the face sheet thickness, other parameters that are varied include the core thickness, core density, face sheet layup, and indentor diameter. The effect of these parameters on the extent of damage is evaluated using the damage metrics of dent depth, dent diameter, and planar area of delamination. When dent depth or dent diameter is considered as the damage metric, specimens containing a higher density core are always found to be the most damage resistant. When planar area of delamination is considered as the damage metric, the eight ply configuration comprised of a lower density core and face sheets containing only small ply angle changes are found to be the most damage resistant. However, this configuration is found to be the least damage resistant when this damage metric is applied to the 16 ply specimens. Rather, the best delamination resistance is provided by a 16 ply configuration with a high density core and face sheets that have ±45° ply groups at the beginning and ending of their stacking sequence.

Design of Artificial Hip Joint by Carbon/PEEK Composites

The purpose of this study is to determine the correct estimation of the various designs for artificial hip joint of the Carbon/PEEK composites. Validity of the study has been tested with the alternative materials for the metal-based materials for artificial hip joint. Moreover, this work evaluated the FEA according to the fiber ply orientation and the condition of load. The stem shape of two kinds was designed through the normal shape of the femur. Three load cases of 1kN, 2.5kN and 5kN were used for each of FEA model. In the case of general shape, the results by ply configuration showed that the stress of ply configuration I was lower compared to ply configuration II and III. On the other hand, in the case of curved shape, ply configuration II were lower compared to ply configuration I and III. The result was checked that the stress of curved shape was higher than that of the general shape in the load of 2.5kN. It could be confirmed then that a similar phenomenon would occur in the condition of 5kN load. However, in the case of ply configuration II, the stress of the curved shape was lower than the stress of the general shape.

Forced Vibration of Delaminated Timoshenko Beams under the Action of Moving Oscillatory Mass

This paper presents the dynamic response of a delaminated composite beam under the action of a moving oscillating mass. In this analysis the Poisson's effect is considered for the first time. Moreover, the effects of rotary inertia and shear deformation are incorporated. In our modeling linear springs are used between delaminated surfaces to simulate the dynamic interaction between sub-beams. To solve the governing differential equations of motion using modal expansion series, eigen-solution technique is used to obtain the natural frequencies and their corresponding mode shapes necessary for forced vibration analysis. The obtained results for the free and forced vibrations of beams are verified against reported similar results in the literatures. Moreover, the maximum dynamic response of such beam is compared with an intact beam. The effects of different parameters such as the velocity of oscillating mass, different ply configuration and the delamination length, its depth and spanwise location on the dynamic response of the beam are studied. In addition, the effects of delamination parameters on the oscillator critical speed are investigated. Furthermore, different conditions under which the detachment of moving oscillator from the beam will initiate are investigated.

Forced Vibration of Delaminated Timoshenko Beams under the Action of Moving Oscillatory Mass

This paper presents the dynamic response of a delaminated composite beam under the action of a moving oscillating mass. In this analysis the Poisson's effect is considered for the first time. Moreover, the effects of rotary inertia and shear deformation are incorporated. In our modeling linear springs are used between delaminated surfaces to simulate the dynamic interaction between sub-beams. To solve the governing differential equations of motion using modal expansion series, eigen-solution technique is used to obtain the natural frequencies and their corresponding mode shapes necessary for forced vibration analysis. The obtained results for the free and forced vibrations of beams are verified against reported similar results in the literatures. Moreover, the maximum dynamic response of such beam is compared with an intact beam. The effects of different parameters such as the velocity of oscillating mass, different ply configuration and the delamination length, its depth and spanwise location on the dynamic response of the beam are studied. In addition, the effects of delamination parameters on the oscillator critical speed are investigated. Furthermore, different conditions under which the detachment of moving oscillator from the beam will initiate are investigated.

An analytical approach for the free vibration analysis of generally laminated composite beams with shear effect and rotary inertia

In this paper, the free vibration analysis of generally laminated composite beam (LCB) based on Timoshenko beam theory are presented using the method of Lagrange multipliers where in the free vibration problem is posed as a constrained variational problem. The effect of material couplings (bending–tension, bending–twist, and tension–twist couplings) with the effects of shear deformation, rotary inertia and Poisson's effect are taken into account. Analytical expression for the natural frequencies and mode shapes are presented. The calculated natural frequencies are verified against some available results in the literature and very good agreement is observed. Furthermore, the effects of some parameters such as slenderness ratio, the rotary inertia, the shear deformation, material anisotropy, ply configuration and boundary conditions on the natural frequency and mode shape are examined.

Analytical solution for the dynamic analysis of a delaminated composite beam traversed by a moving constant force

A closed form solution is presented in this paper to study the dynamics of a composite beam with a single delamination under the action of a moving constant force. The delaminated beam is divided into four interconnected beams using the delamination limits as their boundaries. Governing motion equations are derived in which the differential stretching and the bending-extension coupling are considered. The method of modal analysis is adopted to derive analytically the dynamic response of each beam. The obtained results for the free vibrations of delaminated beam are verified against reported similar results in the literature. Moreover, the maximum dynamic response of such a beam is compared with a healthy beam. The effects of different parameters such as the force velocity, different ply configuration and the size, depth and spanwise location of the single delamination on the dynamic response of the beam are studied. It is noticed that the presence of delamination has significant influence on the dynamic response of the beam.

Semi-analytical solution for the free vibration analysis of generally laminated composite Timoshenko beams with single delamination

A rather new semi-analytical method towards investigating the free vibration analysis of generally laminated composite beam (LCB) with a delamination is presented. For the first time the combined effects of material couplings (bending–tension, bending–twist, and tension–twist couplings) with the effects of shear deformation, rotary inertia and Poisson’s effect are taken into account. The semi-analytical solution for the natural frequencies and mode shapes are presented by incorporating the constraint conditions using the method of Lagrange multipliers. To verify the validity and the accuracy of the obtained results, they were compared with the results from other available references. Very good agreements were observed. Furthermore, the effects of some parameters such as slenderness ratio, the rotary inertia, the shear deformation, material anisotropy, ply configuration, and delamination parameters on the dynamic response of the delaminated beam are examined.