Solid Laminate Research Articles

Study on the flexural load bearing performance of nail-laminated I-beams

ABSTRACT Using nail fastening technology to produce engineered wood by optimizing the combination of solid wood laminates is an effective means to optimize material utilization and reduce manufacturing complexity. This study explored the reliability of nail fastening technology in wood I-beam and analyzed that the connection method between the flanges and webs impacts the bending performance of the I-beam. The results showed that the connection method between the flanges and webs had important influence on the bending performance of the I-beam. The I-beams connected with nails and adhesive had better performance compared to those connected only with nails. Nail and adhesive combination laminated I-beams had a 159.85% and 495.84% increase in ultimate load and initial stiffness, respectively, compared to nail-laminated I-beams. The type of nail was an important factor to the bending performance of nail-laminated I-beams. Compared to round steel nails, self-tapping screws with stronger holding power were more suitable for the construction of I-beams. Installing stiffening ribs at the supports and loading points on both sides of the web enhanced the lateral stability and load-bearing capacity of the I-beams. The ultimate load and initial stiffness of I-beams with stiffening ribs increased by 28.26% and 5.74%, respectively, than the ones without stiffening ribs. The model established based on composite material mechanics theory could accurately predict the ultimate load capacity of self-tapping screw and adhesive combination laminated I-beams.

Damage distribution of composite structures of a certain type of aircraft

Aiming at the damage and repair of aircraft composite structures, the applications and damage of composite structures in a certain type of aircraft, including the wing, fuselage and other components, were counted. Solid laminates (integral panels) and sandwich laminates are typical composite structural forms in the aircraft. Structural damage distribution models with time variable were established, and then the damage distributions of the structures were fitted and tested by structural methods. The results show that the quantitative proportions of damage are 75% for skin delamination, 20% for stringer delamination and 4% for stringer debonding. Lognormal distribution, Weibull distribution and Gamma distribution can all be used to fit the geometric parameter distributions of the three types of structural damage, in which the Lognormal distribution model has the best fitting effect. The distribution of structural damage geometric parameters of one aircraft does not vary with time, and the distributions of geometric parameters of the structural damage between the same type aircraft are also highly similar, which can be expressed in a unified function form.

Thermo-catalytic reforming (TCR) of waste solid grade laminate

Thermo-catalytic reforming (TCR) is defined as intermediate pyrolysis at moderate temperatures and heating rates with subsequent reforming at elevated temperatures using biochar as a catalyst. TCR experiments were carried out to pyrolyze and subsequently reform Solid Grade Laminate (SGL) waste. SGL is a Kraft paper-derived product and as it is widely used in many applications, high volumes of waste laminate must be disposed of at end of life. To assess TCR for SGL waste treatment, the characterisation of the initial feedstock was accomplished, and it concluded that SGL is suitable to be processed via TCR. The main energy carrier products (char, oil and syngas) were generated by TCR in a 2 kg/h pilot-scale reactor under a pyrolysis temperature of 500 °C and reforming temperature of 650 °C, respectively. The mass balance analysis demonstrated that 50 wt% of the initial feedstock was comprehensively converted to syngas, 28 wt% to char and 22 wt% to a liquid fraction containing both water (17 wt%) and organics (5 wt%). The oil showed good properties as its HHV reached a value of 32.72 MJ/kg, with low oxygen and sulphur contents. However further processing is required for the fuels to be within suitable limits for use as drop-in fuels for vehicles. The syngas was found to be rich in hydrogen especially when pyrolysis temperature reaches its maximum. Lastly, char revealed a calorific value of 25.94 MJ/kg and was of a stable form of carbon, exhibiting potential as a feedstock for gasification or as a carbon capture and storage medium. TCR of SGL represents novelty as this feedstock has not been tested before in a pyrolysis/reforming system and it is a promising route in an optic of circularity. In waste valorisation, TCR oil has a great opportunity to be used as a fuel or blended with other conventional fuels, thus supporting the shift towards more sustainable mobility.

Concepts for integrating electrical energy storage into CFRP laminate structures for aeronautic applications

The CleanSky2 THT project SOLIFLY is developing further structural batteries for aeronautical applications. This paper presents the concepts of structural integration and the methodology to evaluate the impact of structural battery integration on the mechanical properties of CFRP solid laminates considering the size and shape of the structural battery insert as well as its location through the laminate thickness. A fully parameterised, computationally efficient numerical strategy for finite element simulation has been implemented to evaluate the mechanical properties and, for the first time, the onset of matrix damage as the cell geometry and integration location are varied. The first mechanical characterisation data of SB cell components and cell prototypes were obtained thanks to multi-instrumented tensile tests using digital image correlation and acoustic emission. An initial assessment of the advantages and trade-offs of the SB integration concepts with respect to functionally separated components is discussed.

The effects of open hole and fiber orientation on Kevlar/Epoxy and Boron/Epoxy composite laminates under tensile loading

Software simulation is the most effective way of visualizing the deformation and stress of materials or structures and hence predicting the maximum force that can be applied before failure or rupture. This paper aims to study the effect of round cut outs on Kevlar/Epoxy and Boron/Epoxy with three fiber orientations using ANSYS. The work is conducted in three stages, mesh convergence analysis, numerical validation of the software used and failure analysis. Failure analysis is conducted by using the finite element method (FEM) with Maximum stress theory as the failure criteria. The results show a significant difference of strength between solid and open hole composite laminates, in which there is a 90% or more reduction in strength for both epoxy laminates. Among Kevlar/epoxy and boron/epoxy, boron/epoxy showed higher tensile failure either in solid or in the lamina with open hole. The direction of fiber orientation also does affect the failure behaviour of the composite laminates. Hence, it is proven that the current study is important in understanding the failure behaviour of the composite plate in which can be useful in contributing the knowledge of these laminates for further study.

Quasi-Static Multifunctional Characterization of 3D-Printed Carbon Fiber Composites for Compressive-Electrical Properties.

Multifunctional carbon fiber composites provide promising results such as high strength-to-weight ratio, thermal and electrical conductivity, high-intensity radiated field, etc. for aerospace applications. Tailoring the electrical and structural properties of 3D-printed composites is the critical step for multifunctional performance. This paper presents a novel method for evaluating the effects of the coating material system on the continuous carbon fiber strand on the multifunctional properties of 3D-printed composites and the material’s microstructure. A new method was proposed for the quasi-static characterization of the Compressive-Electrical properties on the additively manufactured continuous carbon fiber solid laminate composites. In this paper, compressive and electrical conductivity tests were simultaneously conducted on the 3D-printed test coupons at ambient temperature. This new method modified the existing method of addressing monofunctional carbon fiber composites by combining the monofunctionality of two or more material systems to achieve the multifunctional performance on the same component, thereby reducing the significant weight. The quasi-static multifunctional properties reported a maximum compressive load of 4370 N, ultimate compressive strength of 136 MPa, and 61.2 G Ohms of electrical resistance. The presented method will significantly reduce weight and potentially replace the bulky electrical wires in spacecraft, unmanned aircraft systems (UAS), and aircraft.

A Study on the Bonded Flush Patch Repair Method for Aircraft Composite Solid Laminates

An evaluation was performed by applying repair technology of composite solid laminates to airframe composite structures. Damage and defects in the composite laminate structure of an aircraft are caused by events occurring during vehicle movement, such as lightning, tide collisions, and runway collisions during takeoff and landing along with damage caused during aircraft movement and maintenance, fuel injection, and cargo loading. After the damaged part was removed, the damaged composite solid laminated structure was repaired using the bonded flush patch repair method. In the bonded flush patch repair method, the molded patch is joined to the base material using an adhesive. To determine the damage caused by external impact, the test results of the repaired specimen and those of the specimen before damage were compared.

Ecological Footprint Evaluation of Three Types of Wood Flooring in China Based on Their Production Data from 2000 to 2018

To encourage the environmental responsibility of consumers and manufacturers for forest management, it is necessary to evaluate the environmental influences of forest products. Ecological footprint (EF) is an internationally recognized indicator for estimating the natural capital consumption and environmental influences of various forest products. In this study, we developed an accounting model for the EF evaluation of wood flooring, which is a tertiary forest product, by the method of transformation. Next, we used that model to evaluate the EF of three types of wood flooring in China according to their production data from 2000 to 2018. We collected the necessary data by visiting typical enterprises in China and referring to the relevant literature. According to our results, the average EFs of solid wood flooring, engineered solid wood flooring and laminate flooring between 2000 to 2018 were 3.13×106, 1.05×107 and 5.07×106 gha, respectively. The total EFs of solid wood flooring, engineered solid wood flooring and laminate flooring from 2000 to 2018 were 5.95×107, 1.99×108 and 9.64×107 gha, respectively. The coefficients of variation (CV) of the EFs for these three types of wood flooring were 0.45, 0.87 and 0.76, respectively. The average and total EFs of the engineered solid wood flooring were the largest among the three types of wood flooring. The per capita EF and unit EF for the engineered solid wood flooring were also the highest among the three types of wood flooring. The EFs showed an upward trend with irregular fluctuations from 2000 to 2018 for all three types of wood flooring. It is necessary to reduce the EF of the engineered solid wood flooring and use more environmentally friendly products, such as solid wood flooring, for environmental protection.

A model for fast delamination analysis of laminated composite structures

Delamination is one of the major failure mechanisms for composites and traditionally the simulation requires high expertise in fracture mechanics and dedicated knowledge of the Finite Element Analysis (FEA) tool. Yet, the simulation cycle times are high. Geometrically nonlinear analysis approach, which is based on the Reissner-Mindlin-Von K´arm´an type shell facet model, has been implemented into the Elmer FE solver. Altair ESAComp software runs the Elmer Solver in the background. A post-processing capability, which enables the prediction of the delamination onset from the FEA output, has been implemented into the AltairESAComp software. A Virtual Crack Closure Technique (VCCT) specifically developed for shell elements defining the Strain Energy Release Rate (SERR) related to the different delamination modes at the crack front is used. The onset of delamination is predicted using the relevant delamination criteria that utilize the SERR data and material allowables in the form of fracture toughness. The modeling methodology is presented for laminates including initial through-the-width delamination. Examples include delamination in the solid laminate and debonding of the skin laminate in the sandwich structure. Rather coarse FE mesh has proved to yield good results when compared to typical approaches that utilize the standard VCCT or Cohesive Zone Elements.

Effect of core and facesheet thickness on mechanical property of composite sandwich structures subjected to thermal fatigue

Sandwich panels made of polymeric composite materials used in hostile thermal fatigue environments are prone to microcracking due to internal stresses. The impact of micro-cracking as a result of thermal fatigue is more severe in sandwich structures as opposed to solid laminates. Four sandwich panel configurations are studied. They are quasi-isotropic panels made of polymeric carbon fiber reinforced skin bonded by adhesive to honeycomb Kevlar cores. Different facesheet and core thicknesses are investigated. Samples are subjected to thermal cycles from −195 °C to 150 °C. Microscopic inspection is performed at the sample cross-section for a number of cycles to observe the location and density of cracks. It is observed that cracks are formed mainly at the adhesive/composite interface. Also, microcracks are formed more in the core ribbon direction compared to the core transverse direction. For all samples, after 40 thermal cycles, the total crack length becomes saturated and remains almost constant and no more damage happens. To study the effect of microcracks on mechanical property, flatwise tensile test was performed at room temperature. By increasing the number of cycles, the crack area increases and the flatwise strength decreases. Experimental data indicates that the samples with higher core to facesheet thickness ratio has higher microcrack lengths and lower flatwise strength. Therefore, sandwich panels with thinner facesheet and thicker core are more susceptible to the damage if subjected to the thermal fatigue.

Investigation into the production flaws in thin solid carbon laminates by using the ultrasonic phased array method

Investigation into the production flaws in thin solid carbon laminates by using the ultrasonic phased array method

Laminate fibre wave defect – KDF evaluation

The positive side of using composite materials in Aerospace industry is the weight reduction. The drawback are the defects created on solid laminates, during manufacturing. Structure life and strength reduction, due to the defects, need to be accurately evaluated against the A/C airworthiness requirements.

The merits of varying forms of mass timber products for offsite and modular construction

Mass timber is a family of Solid Laminate Timber Systems (SLTS) formed from smaller sections of timber connected by glue, mechanical fixings, moisture movement or a combination of methods. These products, which include Structural Composite Lumber, GluLam, Cross Lam, Nail Lam and Dowel Lam (or Brettstapel), have over the past two decades seen an extraordinary upsurge in use internationally. This global phenomenon has been driven by a greater emphasis on the sustainable use of renewable resources and by significant technological developments in the manufacture of SLTS. This research paper considers the merits of each of these products, their manufacturing processes and the corresponding quality assurance requirements necessary for successful project delivery. The paper describes the advantages and barriers to the use of the mass timber and provides an overview of the various aspects to be considered during design for offsite and modular construction. The work presented also provides case studies of how these products have been researched and utilised into live projects in the UK utilising local resource resulting in the formation of new supply chain arrangements. The work further explains the advantages of the respective systems for the given application including information on species selection, connection systems employed and the necessary onsite and offsite management approaches deployed.

Stress Distribution Investigation at the Tapered Sandwich Endings

Abstract One of the typical sandwich ending is tapered transition to a solid laminate, which causes significant stress distribution changes. The reviewed articles show that tapered area causes increase in the shear stress in the core, increase of the axial forces in the facesheets and local bending at the fork point, at points of the tapering angle change, and at ply drop positions. Most of the studies gave attention to the endings without reinforcing. During Erasmus+ internship at KTH 2D model of the tapered ending with reinforcing plies, various geometry and resin filler in the core tip was investigated to see the influence on the stress distribution. It was found that tension load case is not as critical as bending load case. Increasing of the solid laminate thickness, adding plies and inserting a short resin or adhesive filler into the core tip area lead to significant stress reduction, whereas in the transition point, from tapering to constant thickness sandwich, increasing radius is more efficient than reinforcing plies in regard to reduce stress concentration.

Investigations on the spall and delamination behavior of UHMWPE composites

Composite materials in armor applications are commonly subjected to different deformation and failure mechanisms, which result in delamination of the solid laminate. Direct planar plate impact experiments were executed in order to study spall behavior of Dyneema® HB26. For the first time, the spall behavior of UHMWPE composites was determined by evaluating the free surface velocity measured via Photonic Doppler Velocimetry (PDV). High-speed camera images from lateral view revealed that spall failure of UHMWPE composites, unlike e.g. metals or ceramics, is not restricted to a single crack plane. Instead, the spallation of the composite plates in through-thickness direction caused by the first release wave is accompanied by several delaminations at ply interfaces, which are caused by intersections of subsequent release waves.

Suppression of initial failure at tapered end-closure sandwich panel joint by taper angle change

To examine the configuration of CFRP face plates/foamed plastic core sandwich panel joints, a tapered end-closure-type joint is selected and studied. In this type of joint, the sandwich panel is tapered to form a solid laminate comprising two face plates near the joint, and the two panels to be joined are mechanically fastened at the solid laminate with a splice plate. This type of joint may be suitable for aircraft panels because a flat surface can be obtained at the joint, which is advantageous from an aerodynamic viewpoint. However, in a previous study on such a joint, it was found that a delamination crack initiated from the tapered core end and propagated through the interface between the two face plates as an initial failure mode at a much lower tensile load than the final failure load in a tensile strength test. In this study, the angle of the tapered panel was focused on and the effect of changing the taper angle on suppressing the initial failure was investigated through experiments and numerical analysis. It was found that a smaller taper angle is more effective for suppressing the initial failure.

Low-cost, environmentally friendly route for producing CFRP laminates with microfibrillated cellulose interphase

In this paper, a cost-effective and eco-friendly method to improve mechanical performance in continuous carbon fiber-reinforced polymer (CFRP) matrix composites is presented. Unsized fiber fabric preforms are coated with self-assem- bling sugarcane bagasse microfibrillated cellulose, and undergo vacuum-assisted liquid epoxy resin infusion to produce solid laminates after curing at ambient temperature. Quasi-static tensile, flexural and short beam testing at room temperature indicated that the stiffness, ultimate strength and toughness at ultimate load of the brand-new two-level hierarchical composite are substantially higher than in baseline, unsized fiber-reinforced epoxy laminate. Atomic force microscopy for height and phase imaging, along with scanning electron microscopy for the fracture surface survey, revealed a 400 nm-thick fiber/matrix interphase wherein microfibrillated cellulose exerts strengthening and toughening roles in the hybrid laminate. Market ex- pansion of this class of continuous fiber-reinforced-polymer matrix composites exhibiting remarkable mechanical perform- ance/cost ratios is thus conceivable.

Influence of electric field direction of terahertz radiation on composite materials

Terahertz waves (T-ray) for the non-destructive evaluation were investigated on composite materials. The modalities of the T-ray radiation used were time domain spectroscopy and continuous wave for composites. The composite materials are composed of non-conducting polymeric composites and carbon fiber composites. T-ray signals in the time domain spectroscopy mode resembles that of ultrasound; however, unlike ultrasound, T-ray pulse can detect a crack hidden behind a larger crack (shadow effect). Thick glass fiber reinforced polymer laminates containing double-saw slots was demonstrated. Also, in carbon composites the penetration of T-ray waves was investigated in order to detect flaws is strongly affected by the angle between the electric field vector of the terahertz waves and the intervening fiber directions. Other composites tested in this study include both solid laminates and honeycomb sandwiches. The defects and anomalies investigated by T-ray were foreign material inclusions, simulated disbond and delamination, mechanical impact damage, heat damage, and water or hydraulic fluid ingression. The intensive characterization of T-ray for the non-destructive evaluation of composites are being discussed.

Terahertz scanning techniques for paint thickness on CFRP composite solid laminates

Terahertz ray (T-ray) scanning applications are promising tools. The use of T-ray for nondestructive evaluation was investigated on composite materials. In this characterization procedure, electromagnetic properties, such as the refractive index, were analyzed. The estimates of properties are in good agreement with known data. We successfully demonstrated the characteristics of T-ray propagating through Carbon fiber-reinforced plastic (CFRP) composites to acquire the refractive index by using the characterized material properties. A T-ray technique was developed for measuring paint thickness on CFRP laminates. Good results were obtained from tests performed on standard paint samples with thickness starting from approximately 100 μm. The method was based on reflection mode measurement with time of flight. Another method developed for measuring paint thickness using resonance frequencies was utilized to determine paint thickness on composite laminates. The paint thickness deduced from resonance frequencies agrees well with the result obtained directly from time-domain echoes.

Light-Weight Design of CRH Wind Deflector Panels based on Woven Textile Sandwich Composites

The woven textile sandwich composite (WTSC) is a promising lightweight composite. In bending, two competing core shearing failure modes reduce the strength; deflection induced by the core shearing deformation reduces the flexural rigidity. To replace a solid composite laminate, the span of WTSC panel must be greater than a critical value, which was deduced on the condition that the load capacity and flexural rigidity of the WTSC panel are equal to those of the composite laminate. Three WTSC panels were tested in bending, so that the failure modes were observed, and the critical spans were determined. Using the alternative design method, the WTSC based wind deflector with reduced weight has been fabricated and mounted on the CRH (China Railway High-speed).