Types Of Laminates Research Articles

Application of Haar wavelet discretization method for free vibration analysis of inversely coupled composite laminated shells

In this paper, the free vibration behavior of inversely coupled composite laminated shells (ICCLSs) are studied using Haar wavelet discretization method (HWDM) for the first time. Two doubly-curved shells are inversely coupled on both end of cylindrical shell, in which the doubly-curved shell contains the elliptical, parabolic and hyperbolic shells. The individual shells are coupled by the continuous condition. The boundary condition is modeled by using the artificial spring technique. Based on the first order shear deformation theory (FSDT), the displacement field of coupled shell are established. All displacement functions containing the boundary and continuous conditions are expanded by Haar wavelet series in the meridional direction, and by trigonometric series in the circumferential direction. The boundary and continuous condition functions are contained to satisfy the constants expressed by Haar wavelet series integral form in the function of main system. The convergence and accuracy of current method for the proposed structure are verified by comparison with the finite element method (FEM). The results show that this method is very reasonable for analyzing the free vibration of ICCLSs. Then, the effects of geometric dimensions, fiber orientation angle and lamination type on the natural frequency of ICCLSs are investigated. In end, the new results on natural frequencies and mode shapes of ICCLS are presented, and they will be benchmark data for further research.

An experimental and numerical investigation on low velocity impact response of GLAREs

Glass fiber aluminum laminates (GLAREs) are a type of fiber metal laminates (FMLs) that are widely used in the aviation industry. The present article aimed to carry out the numerical and experimental study of the damage mechanism initiation and development in the FMLs subject to low velocity impact. In the experimental part, the drop weight impact test was conducted at four energy levels of 8, 11.5, 15, and 18.5 J on the GLARE laminates. The first crack in the aluminum layer was observed at 18.5 J in the lower aluminum layer. In the numerical simulation, the user-material subroutine VUMAT, including the three-dimensional Hashin damage initiation criterion and the modified progressive damage evolution model, was coded and implemented in the ABAQUS/Explicit finite element package to predict damage initiation and development. The numerical simulations were validated by the experimental results in terms of force–time, force–displacement, and absorbed energy-time curves. The optical microscopy (OM) and scanning electron microscopy (SEM) images of the specimen cross-section were produced to detect the FML damage pattern. The numericalsimulation andexperimentalresults showed to be in good agreement.

A multi‐scale approach to laminated microbial deposits in non‐marine carbonate environments through examples of the Cenozoic, north‐east Iberian Peninsula, Spain

AbstractThis contribution focusses on stromatolites and oncolites as tools to seek diverse environmental and climate information at different temporal scales. The scales are: (a) Low frequency, dealing with macroscopic and megascopic scales, and (b) high frequency, involving calendar and solar frequency bands. Two depositional environments are used for this purpose: (a) Fluvial and fluvial–lacustrine, which can develop under high to moderate gradients, and in low‐gradient conditions, and (b) lacustrine, subject to low‐gradient, hydrologically closed lake conditions. Several current and ancient examples in the Iberian Peninsula allow high‐frequency and low‐frequency analyses. Within the wedge‐shaped depositional units that fill the high‐ to moderate‐gradient, stepped fluvial systems, stromatolites form half domes and lenticular bodies, commonly at the wedge front. Oncolites are uncommon. These stromatolites developed in moderate to fast‐flowing water in stepped cascades and rapids. Their geometry and extent reflect the topography of the bedrock and later ongoing growth. In low‐gradient fluvial and fluvial‐(open) lacustrine systems the depositional units are tabular, low‐angle wedge‐shaped and lenticular and have great spatial facies variability. The dominant oncoid and coated‐stem limestones form gently lenticular stacked bodies, developed in wide, low to high‐sinuosity channels within wide tufaceous palustrine areas and small lakes. In the Ebro Basin saline carbonate lacustrine systems, stromatolites form thin planar to domed and stratiform bodies and are associated with muddy‐grainy laminated carbonates and very rare oncolites, together forming ramp‐shaped units that represent the inner fringes of high lake‐level deposits. This geometry reflects low‐gradient lake surface and shallow water conditions. Textural and structural features allow different ranks of laminae and types of lamination to be distinguished. Texture, together with the δ13C and δ18O values of consecutive laminae, are useful in distinguishing environmental and climate changes operating over different time spans. Periodicity analysis of lamination can help to discern any temporal significance in the lamination.

The effect of long‐time moisture exposure and low temperatures on mechanical behavior of open‐hole Cfrp laminate

AbstractCarbon fiber composite laminates (CFRP) used in aerospace are operating under various environmental conditions. Parts are often exposed to moisture which slowly diffuses into the laminate and forms internal stresses. During the flight, the aircraft is also exposed to low or elevated temperatures. The result is negative impact on composite performance due to formation of hygrothermal stresses. Understanding this phenomenon helps with prediction of the damage development which is vital for increasing the components service life. The open‐hole CFRP laminates were conditioned in humid air at 70°C/85% RH for 33,800 h and the effect of low temperatures on quasi‐cyclic tension properties and fracture behavior was investigated. The mechanical tests on two types of CFRP laminate with different number and orientation of plies were performed under − 55°C. The material behavior during the testing was monitored by acoustic emission technique. The light optical microscopy and scanning electron microscopy were used for the identification of failure mechanisms. The study showed that the hygrothermal effect has significant impact on materials toughness reduction. The damage mechanisms and characteristic morphologic features are changing due to the matrix degradation and weakened fiber/matrix interface.

Experimental investigation on mechanical and vibration characteristics of Flax/CNSL composite laminates

Natural fiber reinforced composite materials are most increasingly used as sustainable structures in engineering industries due to their vast availability and eco-friendly nature. In this regard, an emphasis is given in the present work to the use of natural fiber in structural composite material in place of synthetic fibers for structural applications. In the present study, the mechanical properties and free vibration characteristics of a pure green composite laminate were experimentally evaluated. For complete understanding of the behaviour of green composite material, a second laminate is prepared using synthetic resin. Two types of composite laminates were fabricated by hand layup method. In the pure green laminate, natural flax fiber is embedded in cashew nut shell liquid (CNSL) resin and for the second laminate epoxy resin is used as matrix. The flax fiber is preferred due to its high mechanical strength among all the natural fibers. Alkaline treatment is done for the natural flax fiber before fabrication to remove impurities and also improve the surface adhesion. Both the laminates were tested for mechanical properties and free vibration characteristics according to ASTM standards. The experimentally evaluated tensile, flexural properties and modal frequency values of two types of laminates are reported and discussed.

In-Plane Shear-Axial Strain Coupling Formulation for Shear-Deformable Composite Thin-Walled Beams

This paper presents an improved description of the in-plane strain coupling in Librescu-type shear-deformable composite thin-walled beams (CTWB). Based on existing descriptions for Euler-type CTWB, an analogous formulation for shear-deformable CTWB is here developed by building, via the Mindlin–Reissner theory and an orthotropic constitutive law of the shell wall, an alternate equation for the in-plane shear force which effectively couples the axial and shear in-plane strains. It is observed that this strain coupling formulation includes some of the transversal (out-of-plane) shear strain terms, thus also functioning as a path for transferring transversal shear energy to the in-plane strain field and therefore improving shear-deformability. The performance of the new CTWB model is compared against that of previously available CWTB (i.e. Euler-type with strain coupling and Timoshenko-type without strain coupling) for several aspect ratios, fibre-orientations and laminate types. Error measures are calculated by comparing several relevant stiffness coefficients and displacement shapes to reference results provided by corresponding 3D shell-based ANSYS finite-element models. Results indicate that for cases involving significant shear energy (i.e. short aspect ratios) and/or in-plane shear-axial strain coupling (i.e. off-axis or asymmetric/unbalanced laminates), the new CTWB model proposed in this work can attain an accuracy level comparable to that associated to more sophisticated models, two to three orders of magnitude larger, at a fraction of the computational cost.

Effect of mechanical anchorage on the bond performance of double overlapped CFRP-to-steel joints

Mechanical anchorage devices have the potential to efficiently improve the bond behavior of Carbon Fiber-Reinforced Polymers (CFRP) Externally Bonded (EB) onto steel with an adhesive. Existing relevant studies, however, have been very limited. Against this background, experimental and numerical studies on the double overlapped CFRP-to-steel bonded joints with an end mechanical anchorage were carried out in the present study. Two types of CFRP laminates (i.e., SIKA CFRP and the other type made in Harbin Institute of Technology – HIT) were used in the bond tests, with or without end mechanical anchorage devices. The test results showed that the end mechanical anchorage had marginal effect on the bond-slip relationship between EB CFRP and steel as well as debonding load, but could increase the ultimate load. It was also found that CFRP laminate from HIT had a better bond performance than that from SIKA, in terms of both debonding load and ultimate load. Using ABAQUS, Finite Element (FE) model was established on such bonded joints and the accuracy was verified with test results. The verified FE model was adopted in a parametric study to further clarify the effect of key parameters on the bond behavior of such bonded joints.

Simulations and Tests of Composite Marine Structures Under Low-Velocity Impact

Abstract Due to their excellent performance, composite materials are increasingly used in the marine field. It is of great importance to study the low-velocity impact performance of composite laminates to ensure the operational safety of composite ship structures. Herein, low-velocity drop-weight impact tests were carried out on 12 types of GRP laminates with different layup forms. The impact-induced mechanical response characteristics of the GRP laminates were obtained. Based on the damage model and stiffness degradation criterion of the composite laminates, a low-velocity impact simulation model was proposed by writing a VUMAT subroutine and using the 3D Hashin failure criterion and the cohesive zone model. The fibre failure, matrix failure and interlaminar failure of the composite structures could be determined by this model. The predicted mechanical behaviours of the composite laminates with different layup forms were verified through comparisons with the impact test results, which revealed that the simulation model can well characterise the low-velocity impact process of the composite laminates. According to the damage morphologies of the impact and back sides, the influence of the different layup forms on the low-velocity impact damage of the GRP laminates was summarised. The layup form had great effects on the damage of the composite laminates. Especially, the outer 2‒3 layers play a major role in the damage of the impact and the back side. For the same impact energy, the damage areas are larger for the back side than for the impact side, and there is a corresponding layup form to minimise the damage area. Through analyses of the time response relationships of impact force, impactor displacement, rebound velocity and absorbed energy, a better layup form of GRP laminates was obtained. Among the 12 plates, the maximum impact force, absorbed energy and damage area of the plate P4 are the smallest, and it has better impact resistance than the others, and can be more in line with the requirements of composite ships. It is beneficial to study the low-velocity impact performance of composite ship structures.

Tensile behaviour of titanium-based carbon-fibre/epoxy laminate

Titanium-based carbon-fibre/epoxy laminates (TI-CF FMLs) are a type of fibre metal laminates (FMLs) formed by stacking thin layers of titanium alloy and carbon-fibre/epoxy laminates to combine the advantages of both constituent materials. Applications in various advanced fields, like aerospace, automotive, infrastructure and marine engineering industries, require such lightweight material with high strength/stiffness and with the capability of absorbing sufficient energy subject to tension. In this study, the tensile behaviour of TI-CF FMLs was investigated under quasi-static loading. A comprehensive experimental study was conducted on twelve different configurations of FMLs as well as their constituent materials (i.e., Ti-6Al-4V, AA 2024-T3, and carbon-fibre/epoxy laminates). The stress–strain curves of the TI-CF FMLs were obtained and characterised into three stages. For comparison, the specific tensile properties of the materials were analysed. Moreover, the specific energy absorption reflecting the energy absorption capacity of the materials was also evaluated. The effects of the types and volume fractions of metal, and the orientations of fibre on the specific tensile performance of TI-CF FMLs were investigated through a parametric study, bringing more insights into the design of TI-CF FMLs under tension. Based on the obtained results, TI-CF FMLs with higher fraction of 0° fibres and with metals featuring better specific strength/stiffness seemed to have enhanced specific tensile performance and improved specific energy absorption before failure.

Estimating self-healing capability of carbon fiber/epoxy composites using ultrasonic guided wave

In this work, two types of self-healing composite laminates with embedded 6 and 12 wt% microcapsules respectively, were prepared. The guided waves were activated and captured using piezoelectric transducer in a pitch-catch approach. Mode I interlaminar fracture tests were conducted using double cantilever beam specimens, and the effects of concentration of microcapsules on the interlaminar properties of specimens were investigated. The interlaminar fracture surfaces of self-healing specimens were observed to support the analysis of mechanical tests and guided wave detecting results. The results show that the self-healing efficiency of specimens with high-concentration microcapsules is less than that of specimens with low-concentration microcapsules. Meanwhile, low-concentration microcapsules reduce the interlaminar properties of specimens. Two guided-wave parameters, namely signals peak value and waveform similarity, were set and correlated with the self-healing capability of specimens. When the specimens were damaged, the peak value of response signals decreases, and the waveform difference between the response signal and reference signal becomes larger. When the specimens were healed, the peak value of response signals rises, and the waveform difference between them becomes smaller.

A Finite Element Simulation of Nano Effects on Stress Distribution in a Below Knee Prosthetic

In the authors’ previous work, various mechanical properties such as modulus of elasticity, strength, creep, impact and fatigue behaviours for different laminates composites with and without different Nano-material additions and reinforcements with different types of fibres were tested experimentally. The four best lamination types and suitable Nano-material percentages were used in this work to develop a numerical investigation of a below knee prosthesis, facilitating the investigation of the effect of different Nano-material types and weight fractions on the stress and deformation in below-knee socket prosthetic structures manufactured from composite laminated materials with various reinforcement fibres. Numerical analysis using the finite element method was adopted to estimate the Von Mises stresses and deformation behaviours for the below-knee prosthetic structures, with the mechanical properties of the relevant composite materials taken from previous published work. The comparison of different Nano-material types and weight fractions suggested that the best Nano-material was SiO2 at a weight fraction of about 2% for the sample 2Perlon+2Kevlar+1Perlon+2Carbon+1Perlon+2Kevlar+2Perlon, where the stress for the socket was reduced by about 40%, with a reduction in the deformation of about 38%.

Lower Triassic (Induan) stromatolites and oolites of the Bernburg Formation revisited – microfacies and palaeoenvironment of lacustrine carbonates in Central Germany

We propose a new facies classification scheme of the cyclic lacustrine carbonates of the Bernburg Formation (Lower Triassic, Induan), with a major focus on the microbial biota and grains. Our data are based on a detailed bed-by-bed outcrop study in Central Germany, within a robust (litho)stratigraphic framework. We concentrate on two intervals of the Bernburg Formation: one around the Calvorde/Bernburg Formation boundary (including the HRZ – „Hauptrogensteinzone“), and a second around the ninth cycle near the upper formation boundary. The textural and mineralogical composition of the two endmember components: skeletal stromatolites and oolites, and the macro-, meso-, and microstructural characteristics (supplemented by μ-XRF-data) allow to classify the carbonates into five lithofacies types. They are interpreted with respect to the development of an ideal lacustrine depositional cycle, embedded between a lake level rise and a lake level fall. The microfacies attributes of the microbialites include various lamination types, shrubs, spherulites, and laminated/clotted/fenestral microfabrics. All sedimentologic (macro-, meso, and microscale) and geochemical data of this study indicate nearshore deposition of the carbonates at marginal shoals in a major endorheic lake (playa lake) with high alkalinity and salinity, and strongly fluctuating lake levels, under arid climates. The lacustrine carbonates are associated with maximum lake expansions, and are laterally interfingering with fan deltas, as indicated by abundant clastic grains in the intercalations of the skeletal stromatolites. The Bernburg Formation microbial buildups reflect changes in lake-level, hydrodynamics and grain supply, and therefore offer insights for the paleoenvironmental interpretation of lacustrine microbialites elsewhere.

Carbon/Epoxy Composites Fabricated by Vacuum Consolidation of the Interleaved Layup of Prepregs and Dry Fibers

The out-of-autoclave (OOA) or vacuum bag only (VBO) process uses partially impregnated prepregs for composite laminates, where gases and volatiles are removed by vacuum through the dry region of the prepregs during the consolidation. In this study, the fully impregnated carbon fiber prepregs and dry carbon fiber were laid up in an interleaved manner to form a hybrid laminate similar to the laminate with partially impregnated prepregs. By using the volumes of the fiber pore and resin in the hybrid laminate, we defined the saturation degree of a hybrid laminate. Three types of hybrid laminates were fabricated and they had different saturation conditions: over-saturation, saturation, and under-saturation. Tensile test was performed to find out how the saturation index affected the tensile properties of the composites. Also, the dual beam focus ion beam system (FIB) was used to observe the cross-section of the hybrid laminate. The result shows that if the saturation index is greater than one, the hybrid laminate will have competitive tensile properties as the composite manufactured by the conventional autoclave process.

In situ synchrotron computed tomography study of nanoscale interlaminar reinforcement and thin-ply effects on damage progression in composite laminates

In situ X-ray synchrotron radiation computed tomography (SRCT) of carbon fiber composite laminates reveals the first-ever qualitative and quantitative comparisons of 3D progressive damage effects introduced by two mechanical enhancement technologies: aligned nanoscale fiber interlaminar reinforcement and thin-ply layers. The technologies were studied individually and in combination, using aerospace-grade unidirectional prepreg standard-thickness (‘std-ply’) and thin-ply composite laminates. The relatively weak interlaminar regions of the laminates were reinforced with high densities of aligned carbon nanotubes (A-CNTs) in a hierarchical architecture termed ‘nanostitching’. Quasi-isotropic double edge-notched tension (DENT) laminates were tested and simultaneously 3D-imaged via SRCT at various load steps, revealing a progressive 3D network of damage micro-mechanisms that were segmented according to modality and extent. For load steps of 0%, 70%, 80%, and 90% of baseline ultimate tensile strength (UTS), intralaminar matrix cracking and fiber/matrix interfacial debonding are found to be the dominant damage mechanisms, common to all laminate types. For both std-ply and thin-ply, nanostitched laminates had qualitatively and quantitatively similar matrix damage modality and extent compared to the baseline laminates through 90% UTS, including relatively few delaminations, despite an ~9% increase in std-ply nanostitched UTS over the std-ply baseline. Complementary finite element-based modeling of damage predicts greater delamination extent in std-ply vs. thin-ply laminates that manifests only between 90% and 100% UTS, offering an explanation for the observed positive nanostitch effect in the std-ply, which is known to be more susceptible to delamination formation and growth than the thin-ply laminates. Thin-ply, with and without nanostitch, intrinsically suppresses matrix damage, as expected from past work and evidenced here by 6.5X less overall matrix damage surface area vs. std-ply baseline laminates averaged over all load steps. These findings contribute new insights from high-resolution experimental mapping of composite damage states that can guide and inform mechanical enhancement approaches and improved damage models.

Višeciljna optimizacija parametara procesa bušenja metalnog laminata ojačanog vlaknima korišćenjem hibridnog GRA-PCA pristupa

This study investigated the effects of drilling parameters and cutting tool coating conditions on the thrust force, surface roughness, and delamination factor in the drilling of fiber-reinforced carbon reinforced aluminum laminate (CARALL) composite, a commercial type of fibermetal laminate. Gray relational analysis (GRA) was used as a multi-objective optimization method to determine optimum processing parameters and principal component analysis (PCA) was used to determine the weights. According to the findings of this experimental study, the most effective control factors for the thrust force, surface roughnes, and delamination factor were the feed rate, tool coating condition-cutting speed interaction, and tool coating condition, with 93.87%, 66.504%, and 29.137% contribution rates, respectively. From the results of the GRA-PCA analysis, the optimum levels of the control factors were determined as 110 m/min cutting speed, 0.1 mm/rev feed rate, and the uncoated tool.

Studies on the validity of the reduced bending stiffness method for eccentrically stacked laminates

AbstractThe reduced bending stiffness method is used in the framework of computational models for stringer stiffened panels. Here, the stringer foot is often stacked on top of the skin of the panel and leads to a stacked laminate with extensional bending stiffness coupling. The validity of the reduced bending stiffness method for the mentioned laminate type is investigated and assessed, as only unsymmetrical laminates without eccentricity have been considered in existing literature. In exemplary studies, the influence of the coupling effects is shown, which allows drawing conclusions on the error that is introduced in, e. g. closed‐form analytical approximate solutions for the buckling of stringer stiffened panels.

"일상의 소재를 이용한 새로운 조형의 실험 -케이블 타이의 결속방법과 이를 이용한 적층식 조형을 중심으로-"

일상의 소재인 케이블 타이(Cable Tie)를 이용한 지금까지의 조형작업들은 기본적인 작업방식이 유사하거나 결과가 특정한 유형에 한계를 가지고 있다. 이 연구는 케이블 타이로 만들 수 있는 새로운 구조의 기본 형태를 제안하고 이를 통해 자립할 수 있는 적층방식의 입체물을 제작하고 시각적 효과를 실험하여 새로운 형태의 입체물에 대한 가능성을 확인하는 것을 목적으로 한다. 새로운 형태의 실험에 대한 타당성과 방향성을 확보하기 위한 연구방법으로 1)케이블 타이 작업의 속성을 이해하기 위한 형태와 질감에 대한 이론들에 대한 검토와 2)2008년부터 발표된 케이블 타이 작업들의 조사와 분석을 진행했다. 케이블 타이의 결합이 만들어내는 형태로부터 점과 선, 면 등의 기본 조형요소들이 있으며 확장된 형태의 입체로부터 비정형성과 유기성을 가진다. 2008년부터 발표된 케이블 타이 작업들을 진행한 주체에 따라 단체와 개인으로 1차 분류하고 각각의 작업들을 조형요소와 조형특성, 구성방식, 형태특징으로 재분류하고 분석했다. 이를 통해 단체작업과 개인작업에서의 규모 차이가 조형특성의 차이로 연결되고 있으며 공통적으로 작업들이 특정한 형태를 유지하기 위해서는 별도의 부재를 필요로 한다는 점을 확인했다. 다음으로 케이블 타이만으로 온전히 자립할 수 있는 조형작업을 위한 실험과정을 단계별로 진행했다. 먼저, 육각형태의 입체를 기본 단위형태(Unit 2)로 제작하고 각각의 기본 단위 형태들이 적층될 수 있도록 확장된 단위형태들(Unit 3, Unit 4)을 제안했다. 단위형태들 간의 상하 맞물림을 통해 구조적으로 자립과 적층이 가능하도록 했으며, 기본형(Unit 2)의 제작과정에서 부분별로 색상을 달리하여 색상 변화의 효과를 실험했다. 최종결과물로서 하단의 흰색에서부터 상단의 적색까지 점층적인 색상 변화를 느낄 수 있는 적층식 입체결과물을 제작했다. 이 작업을 통해 자립이 가능한 독립적인 형태와 색상을 적용한 새로운 조형의 가능성을 확인할 수 있었다는 데 의의가 있다.

The bond behaviour of CFRP-to-concrete bonded joints under fatigue cyclic loading: An experimental study

Carbon fibre reinforced polymer (CFRP) has been accepted by the construction industry as an excellent material for strengthening reinforced concrete (RC) structures against flexural and shear loads. Behaviour of such CFRP strengthened RC structures under quasi-static loading conditions is well understood. Most of the existing studies on CFRP strengthened RC structures under fatigue cyclic loading are focused on demonstrating the effectiveness of the CFRP strengthening on enhancing the fatigue life. However, bond-slip behaviour, a key behaviour governing the performance of flexural/shear strengthened RC structures using externally bonded CFRP, under fatigue cyclic loading remain largely unknown. This paper presents an experimental study aimed at investigating the behaviour of CFRP-to-concrete bonded joints under fatigue cyclic loading. A novel data acquisition system was developed to obtain the strain distribution along the bond length at required force intervals. Experimental results revealed that CFRP-to-concrete bonded joints under fatigue cyclic loading could fail in many different failure modes including, cohesion failure within concrete, cohesion failure within adhesive, and interlaminar failure within CFRP laminate. Failure mode was found to be dependent on the strength of concrete, type of the CFRP laminate, and loading amplitude. Bond-slip relations under fatigue cyclic loading showed that the fatigue damage initiates when the interfacial shear stress is above 80% of the interfacial shear strength.

Influence of metal/composite interface on the damage behavior and energy absorption mechanisms of FMLs against projectile impact

This paper focuses on the interface failure in metal/GFRP laminates on account of the high-velocity impact phenomenon by a hemispherical projectile. The study considers three laminates in which the failure inside the 8-layer 0/90 GFRP laminate is compared with the other two laminates that include metal layers in their layup configuration. The metal layers were placed on the top and bottom on one type of laminates while in the other additional metal layers are placed symmetrically inside the layup as well. They were subjected to high-velocity impact by a hemispherical projectile at different energy levels and the idea is not to perforate the laminate configuration instead to account for the damage incurred in these laminates and the role of metal layers in providing resistance to damage within these laminates. The study utilizes experimental findings and proposes a rate-dependent Finite Element (FE) model consisting of the Hashin-Puck failure scheme for composite and the Johnson-Cook damage model for metal layers. The results of the model satisfactorily agree with their experimental counterparts and provide valuable insight into the damage resistance inside the laminates. It has been observed that the 8-layer GFRP laminate was good in terms of elastic recovery and prevention of propagation of damage inside the laminates only, till the impact energy was lower. For higher impact energy, they show poor damage resistance as the fiber failure is triggered in them. However, laminates with metal layers are shown to protect the laminate by dissipating energy in the delamination of metal/GFRP interface, shear failure of the metal layer, and on account of metal plasticity. The study further shows that the through-thickness compressive stresses were responsible for the failure of laminates and also triggering the delamination in them. A damage energy study was performed to investigate the amount of energy dissipating in various failure modes like delamination, matrix cracking, fiber failure, etc.

Effects of Accelerated Weathering on Degradation Behavior of Basalt Fiber Reinforced Polymer Nanocomposites.

This work aims to give insight on the effect of accelerated weathering, i.e., the combination of ultraviolet (UV) exposure and water spraying, on the visual and mechanical properties of basalt fiber reinforced polymer (BFRP) composites. The solvent exchange method, sonication and high shear milling technique were used to prepare the nanocomposite laminates. Three types of laminates were fabricated, i.e., unmodified BFRP, nanosilica modified BFRP and graphene nanoplatelet (GNP) modified BFRP composites with the total fiber loading of 45 wt.%. Glass fiber reinforced polymer (GFRP) laminate was also prepared for performance comparison purposes between the natural and synthetic fibers. The laminates were exposed to UV with a total weathering condition of 504 h using a Quantum-UV accelerated weathering tester. The weathering condition cycle was set at 8 h 60 °C UV exposure and 4 h 50 °C condensation. The discoloration visual inspection on the tested specimen was observed under the optical microscope. The obtained results showed that the UV exposure and water absorption caused severe discoloration of the laminates due to photo-oxidation reaction. The effect of weathering conditions on tensile and flexural properties of unmodified BFRP composites indicated that the UV exposure and water absorption caused reduction by 12% in tensile strength and by 7% in flexural strength. It is also found that the reduction in tensile and flexural properties of nanomodified BFRP composites was smaller than the unmodified system. It concluded from this work, that the mineral based composites (i.e., BFRP) has high potential for structural applications owing to its better properties than synthetic based composites (i.e., GFRP).