Laminate Thickness Research Articles

Buckling and post-buckling of anisotropic flat panels subjected to axial and shear in-plane loadings accounting for classical and refined structural and nonlinear theories

This article investigates the large deflection and post-buckling of composite plates by employing the Carrera Unified Formulation (CUF). As a consequence, the geometrically nonlinear governing equations and the relevant incremental equations are derived in terms of fundamental nuclei, which are invariant of the theory approximation order. By using the Lagrange expansion functions across the laminate thickness and the classical finite element (FE) approximation, layerwise (LW) refined plate models are implemented. The Newton–Raphson linearization scheme with the path-following method based on the arc-length constraint is employed to solve geometrically nonlinear composite plate problems. In this study, different composite plates subjected to large deflections/rotations and post-buckling are analysed, and the corresponding equilibrium curves are compared with the results in the available literature or the traditional FEM-based solutions. The effects of various parameters, such as stacking sequence, number of layers, loading conditions, and edge conditions are demonstrated. The accuracy and reliability of the proposed method for solving the composite plates’ geometrically nonlinear problems are verified.

Aluminum beam reinforced by externally bonded composite materials

A recently popular method for retrofitting reinforced structure beams is to bond composite plates to their tensile faces. An important failure mode of such plated beams is the debonding of the composite plates from the base material of the beam due to high level of stress concentration in the adhesive at the ends of the composite plate. This paper, shows and presents in more detail a closed-form rigorous solution for interfacial stress in cantilever aluminum beams strengthened with bonded composite (sika wrap) plates and subjected to a uniformly distributed load. The results show that there exists a high concentration of both shear and normal stress at the ends of the laminate, which might result in premature failure of the strengthening scheme at these locations. A parametric study has been conducted to investigate the sensitivity of interface behavior to parameters such as laminate and adhesive stiffness, the thickness of the laminate; the effect on plate length of the strengthened cantilever beam region, the effect of adhesive (modules, thickness) and the effect of loading and geometry for the cantilever beam; where all were found to have a marked effect on the magnitude of maximum shear and normal stress in the composite member. The theoretical predictions are compared with other existing solutions. Finally, this research is helpful for the understanding on mechanical behaviour of the interface and design of the composite-aluminum hybrid structures.

Analysis of Impact Behaviour of Sisal-Epoxy Composites under Low Velocity Regime

The present study concentrates on development of conceptual proof for sisal reinforced polymer matrix composite for structural applications subjected to low velocity impact using a finite element (FE) approach. The proposed sisal-epoxy composite of various thicknesses of 3.2 mm, 4 mm and 4.8 mm is subjected to different impact velocities of 1 m/s, 2 m/s and 3 m/s ranging in the low velocity impact regime to study the energy absorbed and damage mitigation behaviour of the proposed composite. The consequence of velocity of impact and thickness of laminate on the sisal epoxy composite’s impact behaviour is assessed statistically using Taguchi’s experimental design. Outcome of the present study discloses that the energy absorption increases with increased impact velocity and laminate thickness. However, the statistical study shows that impact velocity is predominant factor affecting the impact response of sisal epoxy composite laminate compared to laminate thickness. The role of matrix and fiber in damage initiation is studied using Hashin criteria and it is found that matrix failure is predominant over the fiber failure.

High-velocity impact response of titanium-based fiber metal laminates. Part I: experimental investigations

This two-part article examines the distribution of metallic layers through the thickness of fiber metal laminates (FMLs) on their response and damage when subjected to high-velocity projectile impact. Glass fiber/epoxy and Ti-6Al-4V titanium alloy sheets are used to obtain four different layups of FMLs fabricating by the hand layup process and exhibiting the same thickness of the total metal layer. Part I deals with experimental investigations of fully clamped square FMLs normally impacting at the center by hemispherical steel projectile using compressed air gun set up. Different parameters are considered to evaluate the FMLs’ performance, which includes damage degree, first cracking energy, crack length, deformation profile, and damage developed on the surface and inside the laminate. The results indicate that the highest permanent deformation and cracking are exhibited by FML 4/3-0.3, exhibiting separation of composite layers with different orientations by the metallic layer. The other FMLs exhibit lower and approximately similar permanent deformations. However, lower cracking and a relatively higher lateral delamination spread and opening of the interlayer are exhibited by FML 2/1-0.6 in which composite layers are arranged together than FML 4/3-0.3, signifying that the damage spreading laterally can be reduced by dispensing titanium layers. The ballistic resistance is found to be similar for FMLs. The levels of permanent deformation, cracking, and delamination with their opening and spreading are lesser for titanium-based FMLs than aluminium-based FMLs. The ballistic response of FMLs will be evaluated using analytical modeling in an accompanying study (Part II).

High-velocity impact response of titanium-based fiber metal laminates. Part II: Analytical modeling

This two-part article scrutinizes the influence of metal layer distribution through the thickness of titanium-based fiber metal laminates (FMLs) on their high-velocity projectile impact response and damage. The four different layups of FMLs consist of layers of glass fiber/epoxy and Ti-6Al-4V titanium alloy sheets, exhibiting the thickness of the total metal layer the same. Part I presents the experimental investigations of fully clamped FMLs demonstrating performance parameters, damage mechanisms, and ballistic resistance. Part II concerns the ballistic impact behavior of FMLs using analytical modeling, which is based on test results obtained in an accompanying study. An equivalent mass-spring system is used to obtain the transient deformation, ballistic limit, and absorbed energy of the laminate by various mechanisms. Good agreement is obtained between experimental and analytical ballistic limit velocity. The foremost part of the total energy absorption is by bending and membrane energy absorption (68 % - 72 %), with FML 4/3-0.3 absorbing a higher percentage of aforementioned energies followed by that of both FMLs 3/2 and FML 2/1-0.6. The predicted total energy absorption by several damage mechanisms of FMLs at the ballistic limit displays a reasonable matching with experiments.

Layered self‐resistance electric heating to cure thick carbon fiber reinforced epoxy laminates

AbstractCuring of thick carbon fiber reinforced thermosetting composite laminates has been a major challenge due to the undesired through‐thickness temperature gradient. In this paper, a novel layered self‐resistance electric heating (L‐SRE) method to cure thick laminates was proposed. The thick laminate was divided into multiple independent sub‐layers, and the temperature of each sub‐layer was controlled individually. The experiment's results revealed that L‐SRE was able to achieve highly homogeneous temperature distribution filed through‐thickness both in rapid heating and exothermic reaction stages. The maximum temperature difference of dwell stage for L‐SRE process was less than 4.0°C, and the L‐SRE process that had an optimized thickness of each sub‐layer achieved the minimum mean temperature deviation of 2.1°C, which was 88.46% lower than that of the oven process. By using the optimized L‐SRE method, the maximum value of crosslink thermal overshoot was 12.2°C (32.5°C for oven curing). Different layered temperature control strategies were explored, and the lowest energy consumption of 309.7 Wh (19.82% of oven process) was achieved by using the single‐power pulsed heating. The method proposed in this paper provided a new solution for high‐quality and energy‐efficient curing of thick laminates.

High temperature translaminar fracture of woven-ply thermoplastic laminates in tension and in compression

The translaminar fracture behavior of three composite laminates, based on thermoplastic matrix PEEK reinforced by a woven carbon fibers obtained by consolidation process, has been studied by means of Compact Tension (CT) and Compact Compression (CC) tests. An orthotropic laminate and two quasi-isotropic laminates, have been tested at room temperature (RT) and at 150 °C (i.e. for a temperature slightly higher than the glass transition temperature Tg), with the purpose of evaluation the influence of the stacking sequence and the temperature on the damage mechanisms. The CT type tests show that the temperature influence on the overall mechanical response remains low. In contrast, the CC type tests show a decrease in the mechanical resistance and an augmentation in the global ductile behavior. By means of the 2D Digital Image Correlation and the implementation of a algorithm based on the sigma indicator (confidence interval in the area of interest), the crack propagation was measured during loading, then the G-R curves have been obtained from the compliance method. In tension, there is an increase in the translaminar fracture toughness with the laminate thickness and a slight improvement in this one due to the influence of temperature. In compression, the temperature strongly decreases the translaminar fracture toughness.

Aeroelastic Demonstrator Wing Design for Maneuver Load Alleviation Under Cruise Shape Constraint

Application of the aeroelastic analysis and design framework developed at Delft University of Technology to a design of two aeroelastically tailored composite wings for a flying demonstrator is presented. The objective of the design process is to minimize structural mass of the wing while maintaining a target cruise shape. For this purpose, the jig shape of the wing is parameterized and becomes an integral part of the optimization, while the cruise shape is maintained by means of a constraint. Additionally strength, buckling, aeroelastic stability constraints, and a number of other design requirements have been introduced to obtain a feasible and flight-worthy design. Two wing types were designed: the reference wing and the tailored wing. The difference between the two wings is in the definition of the laminates comprising each wing. The reference wing was designed with symmetric-balanced laminates, while symmetric-unbalanced laminates were used for the tailored wing. The comparison is performed in terms of laminate stiffness and thickness distribution along the span, jig twist, and the aeroelastic response covering elastic deformations, aerodynamic load distribution, and wing root loads, showing a significant mass reduction for the tailored wing compared to the reference wing.

Mechanical Properties of Thin-Ply Composites Based on Acoustic Emission Technology.

Compared with standard-ply composites, thin-ply composites exhibit a superior mechanical performance under various operating conditions due to their positive size effects. Thin-ply laminate failure modes, including matrix initial damage (MID), matrix failure (MF), and fiber failure (FF), have been distinguished through a systematic acoustic emission (AE) signals analysis combined with scanning electron microscopy (SEM). First, the characteristic frequencies of various failure modes are identified based on unidirectional laminates ([90] 68 and [0] 68). Then, according to the identified frequencies corresponding to distinctive damage modes, four lay-up sequences (02[[90m/0m]ns]02, m = 1, 2, 4, 8, n × m = 16) with a constant total thickness are designed, and the effects of the number of identical plies in the laminate thickness on the damage evolution characteristics and the damage process under uniaxial tension loads are dynamically monitored. The obtained results indicate that the characteristic frequency ranges for MID, MF, and FF are identified as 0–85 kHz, 165–260 kHz, and 261–304 kHz, respectively. The thickness of identical plies has a significant effect on onset damage. With the decrease of the number of identical plies (i.e., m in the stacking sequences), the thin-ply laminates exhibit the initiation of damage suppression effects and crack propagation resistance.

Multi-objective approach to optimize cure process for thick composite based on multi-field coupled model with RBF surrogate model

To mitigate the risk of manufacturing defects of thick composite component and improve the efficiency of this process, a multi-objective optimization approach was proposed to optimize the cure process using the multi-field coupled model, surrogate model and genetic algorithm. A multi-field coupled FE model which takes the heat transfer, resin viscosity and resin flow-compaction process into consideration was developed to forecast the cure state of composite. A surrogate model was also built through radial basis function (RBF) to reduce the computational cost and promote the optimization efficiency. After that, the non-dominated sorting genetic algorithm-II (NSGA-II) was combined with the surrogate model to search for global optimum solution. The results indicate that the proposed multi-objective approach proposed in this paper effectively reduce the cure time, maximum temperature overshoot and maximum gradient of DoC simultaneously, hence leading to good performances on thick composite laminate. This work provides guidance in practical design of cure profile for thick composite part.

Suitability of the Subaxial Cervical Laminae for Laminar Screws in the Pediatric Population: A Radiologic Anatomical Study

Introduction: The laminar screw method was popularized during recent years. Since no data exist in the literature on its suitability for subaxial levels in the pediatric population, a radiologic anatomical study was planned to evaluate the suitability of the laminae for laminar screws in children. Methods: The laminar thicknesses from C3 to C7 were measured in axial sections in 120 pediatric patients using computed tomography. The patients were divided into 3 age-groups: ages 4–6, 7–9, and 10–12. Each age-group consisted of 20 boys and 20 girls. The suitability of the laminae was evaluated for 3.5-mm-thick commercially available screws and also for the 3-mm screws that could be produced in the future. If the height of the base of the spinous process is ≥ 9 mm, the segment was accepted as suitable for the bilateral screw, and ≥5 mm is for the unilateral screw. Additionally, laminar thickness and length were measured for possible short screws longer than 15 mm in the laminae that were distally thin but proximally thick. Results: The C4 and C5 levels had the thinnest (2.77 ± 0.6 mm and 2.81 ± 0.6 mm, respectively) and C7 had the thickest laminae (4.66 ± 0.6 mm) in all age-groups. No significant differences were found between boys and girls and right and left laminae. According to the age-groups, an increase in laminar thickness was possible by growing, but only C7 laminae thickness was statistically different between 10–12 and 4–6 age-groups (p < 0.001). The last rate of the suitability was 9.1% for the 3.5-mm-thick screws and 13.75% for the 3-mm-thick screws after deletion of the bilateral insertion due to the short base of the spinous process and adding the possible short screws in the distally thin but proximally thick laminae. The rates increased with age, but the only statistically significant difference was found between 4–6- and 10–12-year-old age-groups (p < 0.001). Conclusions: Laminar screws may be suitable for some levels of C7, C6, and C3 even in the young pediatric population. The use of thinner screws (3 mm) may increase the suitability rate. Therefore, laminar screw choice may be considered as a salvage method in pediatric patients, and all laminae may be evaluated individually for suitability. This study did not evaluate the safety and efficacy of the method in children, and these issues must be studied further.

Salinity stress mitigation of some canola cultivars grown under South Sinai conditions using magnetic water technology

Salinity stresses either in irrigation water and/or soil is one of the most serious agricultural problems facing farmers in arid and semi-arid regions included Egypt. Many are as in the Sinai region depend mainly on the underground water of various degrees of salinity that prevent cultivated crops from reach to the full yield.Under these conditions,a split-plot field experiment using three canola cultivars; Pactol, Serw-4 and Serw-6under three irrigation water treatments:i) Brackish-water (BW), ii) Magnetic-BW1; brackish water after magnetization through passing a three inch static-magnetic unit,3.75 mT,produced by Delta Water Company, Egypt and iii) Magnetic-BW2;brackish water after magnetization through passing a three inch static magnetic unit, 0.75 mT,produced by Magnetic-Technologies Company, UAE,was carried out at Agricultural Experimental Station of Desert Research Centre, Ras Sidr region, South Sinai Governorate, Egypt during the 2017/18 winter season. The results showed that irrigation with M-BW1or M-BW2surpassed irrigation with BW in all tested growth parameters (plant height, branches and leaf number/plant, leaf area, dry matter of leaves, stem and total plant,and total chlorophyll); leaf anatomy(instance, mid vein and lamina thickness, length and width of leaf vascular bundle and lower and upper epidermis thickness); stem anatomy(stem diameter and thickness of cortex, xylem and phloem in addition pith diameter)and chemical analysis for mineral content (N, P, K, Mg, Fe, Cu, Zn ) at 85 days after sowing (DAS). As an average of both magnetically brackish-water treatments over tested three canola varieties, the percent of improvement compared to irrigation with brackish-water ranged between 10.78-16.02% for growth parameters, 28.33-31.76% for dry matter of plant; 15.58 -80.81% for leaf;10.71-63.88% for stems and2.42-54.48% for mineral content of leaves at 85 DAS.Reverse trends were observed in the best indicators for alleviation salinity stress (Na, and proline),where these decrease dunder both magnetic brackish water treatments by 66.08 and 43.75%, respectively (average of both magnetically brackish-water treatments compared to BW water treatment). Generally, the three tested canola varieties showed a positive response under magnetic brackish water treatments. The positive results in above-mentioned parameters of vegetative growth reflected improvement in canola yield and its components. The percent of improvement ranged between 9.35and35.98 for yield components and reached1.29,19.66 and21.30% in seed oil percentage, seeds and oil yield (kg fed-1;fed=4200m2), respectively compared to brackish water.

An experimental study on bond strength of abaca fiber as natural FRP material

The use of fiber reinforced polymer (FRP) has been implemented as an alternative for strengthening and repairing methods. Nowadays, the use of natural material for FRP has been developed in order to minimize the disadvantage effects to nature due to synthetic FRP material and economic reason. In this paper, an experimental study was carried out to evaluate the bond strength of abaca fiber as natural reinforced polymer (NFRP) material in reinforced concrete (RC) beams. The test specimen was a beam that had cross-section area of 100 × 100mm2 and 300mm length. Single rebar was used in this study with 10mm diameter of rebar. Artificial crack was applied in order to consider the initial crack by using cardboard between the concrete. Two externally bonded strengthened beams with a different type of abaca fiber arrangement, bond length, and thickness were applied on the concrete surface. The test was conducted by applying a tension load on the beam until the specimen reach its failure. The results showed that the bond strength decrease as the bond length becomes longer because the maximum load was almost constant for different bond length. The maximum load was approximately around 4 tf for short and long bond length. The compatibility of abaca fiber and rebar was also monitored. Both abaca fiber and rebar able to stand the load compactly. Abaca fiber composite laminate had a similar trend with rebar at the same location where an artificial crack was made. Furthermore, the arrangement and thickness of the abaca fiber composite laminate affected the results.

Research on 3D Printing layered Algorithm based on FDM Technology

Fused deposition forming (FDM) is the most mature 3D printing technology, which has been widely used in many fields of our daily life, science and technology, and economic development.In the molding process of the model, how to choose the appropriate layering method has become the key point to improve the precision and efficiency of 3D printing. Based on adaptive layered algorithm was studied, using three-dimensional modeling software of entity modeling, the introduction of the z axis curve contour curve is determined, and then segment, find out each section contour tangent to the curve, calculated the contour tangent with the model the Angle between the positive direction, an analysis model of layer thickness;The lamination thickness of the model is calculated by using probability statistics, summation superposition and other mathematical methods.Practice has proved that the adaptive layering method is clear in process and simple in calculation, which reduces the workload of layering to a certain extent and improves the precision and efficiency of 3D printing molding.

Experimental study on the flexural behavior of RC beams strengthened with prestressed BFRP laminates

In this study, the flexural behavior of RC beams strengthened with prestressed basalt FRP (BFRP) laminates was investigated. Compared with the conventional carbon FRP (CFRP) laminate, BFRP exhibits a larger failure strain but lower modulus, in addition to its high strength and prominent creep rupture behavior; this makes BFRP a suitable option for cost-effective strengthening of existing beams. Nine specimens were prepared to investigate the effects of the FRP type, laminate thickness, strengthening method, reinforcement ratio, prestressing level, and adhesive on the flexural behavior of RC beams. The differences in the failure mode, L-D curve, cracking behavior, and strain development of concrete, steel, and FRP laminate were analyzed. The results demonstrated that specimen strengthened with BFRP laminate could achieve 85% of the loading capacity of the specimen strengthened with CFRP laminate under the same laminate section and but ensured a superior crack control effect and ductility. Meanwhile, a higher prestressing level led to a higher material utilization of BFRP, and the prestressing method lowered the reinforcement ratio effectively. Moreover, the bonded system had a better crack control effect and higher laminate strength utilization ratio than the unbonded system did.

Manufacturing influences of the adhesive layer on the load-bearing capacity of anchor bolts for thick FRP laminates

The subject of this study is the load introduction concept of adhesive bonded anchor bolts for local load transmission into the cross section of fiber-reinforced polymer (FRP) composites. Anchor bolts and glued-in rods are a standardized load introduction in civil engineering. However, this concept is not yet examined for FRP structures in the open literature.The objective of this study is the experimental analysis of macroscopic irregularities induced by the manufacturing process of the adhesive layer. Three properties of the adhesive layer were examined: the thickness due to the position of the bolt, the presence of voids and the contour of the adhesive spew. The manufacturing process was optimized with regard to each property. The influence of the macroscopic irregularities was determined by tensile pull out tests. The results showed that the joint is capable of transmitting high loads into the laminate. The determined influence of the manufacturing process on the mean load-bearing capacity was not distinct, but a defined fillet contour resulted in a very low sample standard deviation.

Effects of spacing and ply blocking on the ballistic resistance of UHMWPE laminates

It is commonly claimed that ultra-high molecular weight polyethylene (UHMWPE) laminates offer high energy absorption during projectile impact with a cross-ply configuration. In this study, we explored alternative configurations with the aim of achieving better ballistic resistance than that of the cross-ply architecture. The UHMWPE laminates were fabricated from Endumax® cross-ply SHIELD XF23 using a hot press machine and material properties were obtain from Endumax® unidirectional (UD) tape TA23 coupon specimens. A solid steel sphere was used as the projectile. It was found that thinner laminates have higher the specific ballistic limit suggesting that it is more effective to deploy multiple stacks of thin laminated panels spaced apart than to bond all the laminas to form a single thick laminate. Experiments confirmed that while the multiple laminate systems always outperformed a single laminate comprising the same number of laminas, it was also best not to space the laminates apart. When simply stacked without spacing, the multi-laminate arrangement significantly enhanced the ballistic performance (about 10% increase in ballistic limit over the single panel). Adjacent laminates in the multi-laminate system were then rotated 45o relative to each other and then bonded together to form a single laminate with multiple blocks of similarly oriented laminas. This ply block configuration also had higher ballistic limit than the single cross-ply laminate for thin laminates but showed no advantage for thick laminates.

A feasibility study on high-power fiber laser cutting of thick CFRP laminates using single-pass strategy

High-power fiber laser as an emerging technology has been developed for machining composite sheets (less than 5.0 mm thick) with relatively high efficiency, while very limited works are reported when using fiber laser to cut thick CFRP plates. In order to further explore the cutting capability of fiber laser system without sacrifice of efficiency, a feasibility study on high-power fiber laser cutting of thick CFRP laminates using single-pass strategy was carried out in this work. Surface morphology and cross-section characteristics were analyzed for further understanding laser-CFRP composite interaction/removal mechanisms. Various thermal defects were qualified to better understand the influence of processing parameters on machining quality. Results showed that relatively high level of laser power (4800 W) and cutting speed (2000 mm/min) were preferred to effectively improve surface quality and cut through samples during laser cutting process, while excessive laser energy damaged CFRP composites with severe cracks and delamination mainly due to high level of thermal stress. CFRP laminate with a thickness of 10.0 mm could be successfully cut through when using high-power fiber laser and single-pass strategy, the threshold of energy per unit length was about 270 J/mm. Experimental results from this work can provide significant benchmark data for further industrial applications.

Study on kerf characteristics and surface integrity based on physical energy model during abrasive waterjet cutting of thick CFRP laminates

Abrasive waterjet machining was an effective method for cutting CFRP materials in various industries, while machining defects are inevitably observed especially for thick CFRP laminates due to the inherent characteristics of waterjet. In this work, a full factorial experimental array was employed totally involving 18 trials when using abrasive waterjet to cut CFRP laminate up to 10.0 mm thick. The influence of process parameters including hydraulic pressure, traverse speed, and stand-off distance on jet energy was deeply analyzed and the power-to-speed ratio (Ė/u) parameter was obtained, which was combined with the physical energy model of abrasive waterjet based on the energy method. The influence of process parameters on kerf characteristics/surface integrity and the mechanism of defects were further analyzed. Various surface defects along thickness direction were observed and corresponding mechanisms were investigated. Results showed that higher hydraulic pressure, lower traverse speed, and stand-off distance within in the selected range were preferred to obtain better surface quality. From the perspective of power-to-speed ratio (Ė/u), the surface roughness decreased rapidly up to ~ 68% with Ė/u increased from 20,000 to 40,000 J/m. When it exceeded 40,000 J/m, the downward trend gradually reduced and even became stable in the case of high stand-off distance. The level of kerf width generally increased with the increase of Ė/u irrespective of stand-off distance.

Vacuum-Assisted Hot-Forming Using Tailored Laminate Temperature

A non-isothermal vacuum assisted hot-forming process using tailored laminate temperature is introduced. By using process simulation and manufacturing experiments, improved laminate quality is achieved compared to the standard hot-forming process. Furthermore, it is also shown that the manufacturing time in the clean room can be reduced to one tenth of the standard process time. In this study 8.4 mm thick quasi-isotropic laminates from unidirectional prepreg were laid up flat with an automatic tape laying machine and hot-formed to a U-shaped laminate. The laminates were then cured in a concave mould with standard bag on the inside. A complete tailored temperature hot-forming cycle of 7.5 min produced a very good final laminate quality with a total thickness variation as low as 4.0% and without wrinkles or indications of porosity. With a 4 min hot-forming cycle the thickness variation was also acceptable at 8%.