Tensile Strength Of Laminates Research Articles

Sensitivity analysis methodology to identify the critical material properties that affect the open hole strength of composites

Aeronautical industries are concerned about generating efficient and cost-effective statistical design allowables of composite laminate responses. Within this framework of uncertainty quantification and management (UQ & M), accounting for the various uncertainties is crucial to calculate the design allowables which, in turn, adds confidence to the design and certification process. In this context, as a precursor to UQ & M, we establish a global sensitivity analysis framework to identify the material properties that influence the laminate responses. In this study, an open hole tensile (OHT) test configuration is considered. In a first step, sensitivity analysis based on an analytical model is performed using Sobol, FAST, and Morris methods, whereas in a second step, sensitivity analysis based on a detailed 3D finite element model (FEM) incorporating damage is performed using Morris. The paper compares different sensitivity approaches in terms of computational cost and results. Further, different case studies (varied notched hole sizes, width-to-diameter ratios, laminate stacking sequences, etc.) are performed to study how the sensitive parameters vary for different configurations. The study identified the Morris method, along with the selected hyper parameters, as being suitable for FEM based sensitivity analysis due to its low computational cost. Five material properties (out of 23) were identified as influencing the open hole laminate tensile strength. Using the FE simulations performed for the Morris analysis, a first estimation of the design allowables (A and B basis values) on the OHT strength is also presented. The results from this paper contribute to the next step of UQ&M, where only the identified sensitive material properties can be considered for detailed experimental characterization or for building meta models to calculate the design allowables. A framework like this, complements experimental campaign to reduce the associated costs and knock-down factors, thus shortening the certification process.

AEROPLAS – Desarrollo de componentes para la industria aeronáutica mediante tecnologías de bajo coste

The future of the aeronautical sector is oriented towards manufacturing lighter and more profitable structures and components, using more ecological materials and technologies, that allow reducing costs, weight and fuel consumption, with shorter manufacturing cycles, while increasing energy efficiency manufacturing. AEROPLAS project arises in this context, with the aim of contributing to the advanced manufacturing process of thermoplastic composites using low-cost technologies for the aeronautical industry. This study focuses on the replacement of aeronautical parts currently manufactured in thermosetting composite by thermoplastic ones, in two real components: cover panel and access door of the ventral fairing of A350, using two materials of different quality: LM-PAEK/CF semipreg (TenCate Cetex® TC1225) and PC/CF prepreg (ePreg245CHT/PC40). Through design and calculation, the stacking and part thicknesses necessary to cover the structural requirements of both components have been obtained, based on the data acquired from the characterization of the base materials. Two manufacturing processes have been studied and compared to obtain the new parts, selecting thermoforming and stamping as the most promising. Finally, the characterization of the pieces obtained has been carried out by means of non-destructive tests (visual inspection, ultrasonic verification, dimensional inspection using laser tracker) and destructive tests (pull-out strength on riveted joints [AITM1-0066], bearing strength [AITM1-0009], laminate tensile strength [AITM1-0007], fastened joints strength [AITM1-0067]).

Research on damping performance and strength of the composite laminate

In this paper, the influence of E-glass fiber volume fraction and laying angle on the damping and strength of composite laminates was comprehensively analyzed. By increasing the fiber laying angle and reducing the glass fiber volume fraction, the damping capacity of the composite laminate was increased, but the tensile strength of the laminate was reduced; By reducing the fiber laying angle and increasing the glass fiber volume fraction, the tensile strength of the composite laminate was increased, but the damping characteristics of the laminate was reduced. In addition, in the damping experiment of composite laminates, in order to avoid the influence of external damping sources, the vacuum non-contact damping test method was adopted in this paper, and the influence of air damping on the damping experiment results of composite laminates was comparatively analyzed. The results of comparative experiments showed that air damping had a very obvious influence on the damping of composite laminates, especially when the damping of composite laminates was small, the influence of air damping would be greater.

Effect of bio waste (conch shell) particle dispersion on the performance of GFRP composite

The mechanical properties as well as sustainability of the fibre reinforced composites in the varied environment has need analyzed by researchers with particle dispersion favouring property enhancement. In this present work, crushed conch shell particles are used in composite making. Conch seashells begin harmless to the environment, used in many artistic works has finds its engineering application recently. In this line, conch shell particles of sieve size 600μm and below is dispersed in varying weight percentage (25%, 35%, 45% and 55%) in the making of E-glass fibre epoxy composite by hand lay-up technique. The significance of conch particle addition in the glass fibre reinforced polymer (GFRP) composite has been evaluated by mechanical characterization and dynamic mechanical analyzer (DMA). Tests as per ASTM standards are conducted on the prepared GFRP laminate with and without particle dispersion. The impact energy of the laminate with 35% conch particle records a higher value of 29.80J than the laminate without conch particle (11.52J). Whereas, the tensile strength of laminate with 35% conch particle is 405.7MPa with 10% rise than without conch (364.7MPa). The dynamic mechanical analysis revealed the possibility of marginal raise in glass transition temperature (Tg) and reduction in loss modulus (E″ on conch particle addition. The extent of conch particle contribution to the mechanical properties is substantiated by surface morphology. Thus, this work directs the application of conch particle bio-waste as particulate filler in the composite with an ability to enhance property.

Tensile strength of Z-pinned laminates in RTD and hot-wet environment

Abstract Experiments and simulation analysis for tensile strength of Z-pinned laminates were conducted in both room temperature and dry and hot-wet environments. The results of the experiments show that the fracture of [0]6 specimen with Z-pins was longitudinally torn, and there was a row of Z-pins at the fracture of [(±45)/(0,90)]2S specimen with Z-pins. It could be observed that the hot-wet effect on the tensile strength of the Z-pinned laminates increased with percentage of 0-direction fibers decreasing in the laminates from the experiments of the unidirectional tape laminates and the woven cloth laminates. When the volume content of Z-pin increased, the hot-wet effect on tensile strength of Z-pinned [45/0/-45/90]2S laminates with Z-pins would become smaller and smaller. The simulation method of the hot-wet effect on tensile strength of the laminates was combined with the experiment and the finite element analysis. It used 14 nonlinear springs to simulate the longitudinal tearing of [0]6 specimen with Z-pins. The simulation results showed that Z-pin played a role of fulcrum, and because of the lever principle, the fiber bundles were torn at both tips in resin-rich area.

The effect of the microstructure of porous alumina films on the mechanical properties of glass-fiber-reinforced aluminum laminates

The glass-fiber-reinforced aluminum laminates were obtained by anodizing aluminum alloy under anodizing voltage of 10, 20, and 30 V in the 200 g/L H3PO4 electrolyte. Scanning electron microscopy (SEM), short beam, and tensile tests were employed to determine the surface morphology, interlaminar shear strength (ILSS) and tensile strength of laminates, respectively. The results also show that the epoxy penetrates into the pores of the anodic films, and this is the mechanism of adhesion. The ILSS and tensile strength of the anodized specimens (under 20 V) respectively increased by approximately 50 and 15% comparing with those of the non-anodized specimens. This increase of mechanical properties results from the porous surface of aluminum providing greater mechanical interlocking to epoxy. The ILSS and tensile strengths of the anodized specimens increased with the increase of anodizing voltage from 10 to 20 V; however, it decreased when the voltage further increased to 30 V. It is considered that the microstructure evolution of the porous films has a significant effect on the mechanical properties of the laminates.

Effects of Stitching Parameters on Tensile Strength of FRPs under Hygrothermal Conditions

An investigation based on experimental and analytical approaches was conducted to evaluate the behavior of the stitched laminates under hygrothermal conditions. Tensile strength of laminates under different environmental conditions was predicted using FEM model. Effects of stitching parameters upon strength performance of laminates were studied using FEM model and validity of results was checked by comparing with the experimental results. Test results have shown that hygrothermal environment condition has no significant effect on the tensile strength of unstitched laminates, but improved the strength of stitched laminates significantly. Stitching decreased the tensile strength of laminates under 20°C dry environment; however, it improved the tensile strength under 20°C wet environment. It was also found from analytical results that, the failure strength of stitched laminates is higher for smaller thread radius (R<0.25) and relatively greater (5~6mm) stitching distance (5~6mm).

Enabling damage detection: manufacturing composite laminates doped with dispersed triboluminescent materials

Triboluminescent materials are being harnessed to address the gaps in current structural health monitoring systems. Their innate ability to emit light when stressed or broken makes them ideal candidates for the ubiquitous and in situ monitoring of structures. The increasing use of advanced composites in critical structures, where subsurface damage initiation may go unnoticed, further highlights the urgency in developing efficient online monitoring technologies. This work looked at the manufacturing of composite laminates that have been doped with various concentrations (0 to 10 %wt.) of a triboluminescent material (ZnS:Mn). Laminates were manufactured using a vacuum infusion process. Dispersing the ZnS:Mn particulates was cumbersome because their density was higher than the resin that caused settling during resin infusion. The dispersion of ZnS:Mn is critical to their use in the health monitoring of the host structure. As such, a method for mechanical agitation using a rotational vacuum infusion apparatus was developed employing centrifugal motion. The degree of dispersion in the resulting laminates was determined using scanning electron microscopy and the energy dispersive scanning feature of the electron microscope for elemental mapping. A quantitative metric was established by computations of the Euclidean distance of EDS mapping. Studies of the effect of ZnS:Mn concentration on the tensile strength of laminates showed that increasing the ZnS:Mn concentration reduced the tensile strength. Key processing parameters were studied, and determined that curing kinetics were not altered by ZnS:Mn inclusion.

Transparent, tough collagen laminates prepared by oriented flow casting, multi-cyclic vitrification and chemical cross-linking

The lamellar architecture found in many natural fibrous tissues has a significant bearing on their specific functions. However, current engineered tissues have simultaneously no realistic structures and no adequate functions. This study demonstrates a two-step process for obtaining structurally mimicking laminates in natural fibrous tissues with good optical and mechanical characters from purified-clinically-safe collagen molecules. Stacked lamella structures can be created by repeating flow casting, with the controlling parallel/orthogonal directionalities of each thin single-layer (2–5 μm in thickness). The transparency of laminates is successfully improved by a unique multi-cyclic vitrification with chemical cross-linking. The directionalities of optical and mechanical functions in laminates are strongly related with the preferential collagen alignments in the laminates. The tensile strength of laminates is extremely higher than any other engineered materials as well as native cornea, which exhibit an orthogonal laminated collagen structure and a good optical transmission.

Influence factors analysis for residual tensile strength of composite laminates after impact

The impact damage process and residual tensile strength after impact of laminated composites are analyzed by the whole-process analysis method and 3D progressive damage theory. The influence of impact energy, impact tup, composite materials, and ply orientation angles on the impact damage and residual tensile strength of laminated composites are researched, which provides the guidance for the structure design resisted impact of laminated composites.

Hygrothermal and Stacking Sequence Effects on Carbon Epoxy Composites with Molded Edges

Moisture and high temperature may cause a variety of effects on the mechanical and thermophysical properties of polymeric composites. The diffusion of moisture in the laminate occurs primarily by capillarity until a state of equilibrium is reached. Moisture affects the matrix and the fiber/matrix interface. The stacking sequence and the free edge finishing may affect the laminate tensile strength causing a free edge delamination; they can also affect the moisture absorption process. Laminates produced with molded edges do not require machining operations for the trimming and finishing of the free edges causing a gain in productivity. However, the mechanical behavior of laminates with molded edges saturated with moisture has not been characterized. This work presents a comparative study of the tensile strength of cross ply laminates with molded and machined edges under dry condition and saturated with moisture.

The Effect of Environment on Tensile Properties of Stitched and Unstitched Laminates (with a Hole)

Tensile tests are conducted on stitched and unstitched uniweave T300/QY9512 laminates (with a hole) in hygrothermal environment and normal environment. It is shown that in a normal environment stitching reduces the tensile strength of laminates and does not significantly alter the open-hole tensile strength. The hygrothermal environment has a beneficial effect on the tensile strength of laminates and open-hole laminates, especially of stitched specimens. It is also noted that stitching direction has no effect on the tensile properties.

Characterization of Matrix Crack-Induced Laminate Failure—Part II: Analysis and Verifications

A two-part investigation was performed to study the stiffness response and strength of composite laminates subjected to uniaxial tension. In Part I, experimental testing was performed to characterize the matrix crack-induced damage progression and failure modes in composite laminates under uniaxial tension loading conditions. In Part II, analytical models were developed to account for the damage modes observed in the experimental investigation. Models for matrix crack-induced delamination, matrix crack-induced microcracking, and matrix crack-induced edge delamination were developed. Model predictions were compared with experimental data. The proposed models were integrated and implemented in the computer code, PDCell. The code was then used to predict the stiffness response and failure of composite laminates subjected to tensile loading. Code predictions were used to evaluate the effects of ply orientation, ply group thickness, loading direction, and stacking sequence on laminate tensile strength. The predictions from the code were compared with available test data in the literature.

Influence of fibre length and concentration on the properties of glass fibre-reinforced polypropylene: Part 3. Strength and strain at failure

Abstract In this report we present the results from the third part of a study on the influence of fibre length (0.1–50 mm) and concentration (3–60% w/w) on the properties of glass fibre-reinforced polypropylene laminates. These laminates were prepared in the laboratory using a wet deposition method and compared with samples prepared on a commercial melt impregnation GMT line. We found that laminate tensile strength increased linearly with fibre concentration up to 60% w/w. Laminate strength was also found to increase with increasing fibre length. At high values of fibre length (> 3–6 mm) the strength reached a plateau level which was directly dependent on fibre content. The matrix molecular weight appeared to have little direct influence on the level of laminate strength. However, the glass fibre sizing compatibility was found to have a strong effect on the tensile strength of both laboratory made wet deposited laminates and commercially prepared GMTs. The tensile strength of the GMT samples also showed a clear correlation with the measured fibre strength. A modified version of the Kelly-Tyson model gave calculated values of laminate strength which correlated well with the experimental data. We propose that the tensile strength of these laminates is governed by the properties of the fibres which have an orientation close to parallel with the loading direction.

Fracture Scaling Parameters of Inhomogeneous Microstructure in Composite Structures

The influence of inhomogeneous microstructure on fracture properties is presented in this study. Previous tests have shown an improvement in the notched tensile strength of laminates manufactured with fiber placement versus hand layup for the same materials and laminate configuration. Fiber placement results in structures with a more inhomogeneous microstructure than in conventional hand layup manufacturing. Equivalent continuum modeling was employed to study this phenomenon. A specialty, couple stress (Cosserat Theory) finite element was developed to explore the influence of inhomogeneities in regions of high stress gradients such as notches. The results indicate that the addition of the couple stresses mitigates singularities at notch tips. In particular, it was shown that geometry alone is not sufficient for proper scaling if inhomogeneities exist. A two-parameter failure criterion, based on critical strain energy release rates and an inhomogeneity parameter, is proposed. Good correlations were found between predictions and experimental results.

回転ディスク法によるＡｌ‐１２ｍａｓｓ％Ｓｉ合金急冷凝固積層材の作製

Possibility of making laminate, which is made directly from molten metal and the rapidly solidified aluminum alloy foils were laminated, was investigated. To laminate foils into multi-layer laminate from molten metal, rotating disk process was devised. Sticking of the first foil and laminate to the surface of the disk is most important to make the laminate. Fundamental factors which affect sticking length of the foil are disk temperature, disk speed, disk material, number of slit. Disk was heated up to 100°C. Disk was made from SUS304 and rotating speed was up to 47m/s. Nozzle which has 1-7 slits was used to eject molten metal. Al-12mass%Si alloy was melted in air and ejected onto the disk. Laminate consisting of more than 50 layers of foils can be cast by rotating disk method. Cooling rate of laminate in the range of 103-104°C/s is attained. There is not much difference in cooling rate of each layer. Tensile strength of laminate is about 300Pa. Each layer of the laminate is not torn along interface by bending.

Residual Tensile Strength Prediction on a Ply-by-Ply Basis for Laminates Containing Impact Damage

Impact loading on composite laminates can cause surface or internal damage in the form of fiber breakage, delamination and matrix cracking. Such damage can reduce laminate tensile strength. In the work presented here, impact damage was modelled as part through-the-thickness damage and laminate residual strength was evaluated by ex amining the behavior of each individual ply of the laminate. A residual strength prediction procedure, proposed previously for laminates containing cut internal fibers, was used here for laminates containing impact damage. The prediction of laminate residual strength was performed based on 3-D finite element results in conjunction with a principal load carry ing ply failure criterion. The predicted residual strength agreed with the experimental data within the bounds of 0.85 to 1.08 times the experimental data, indicating the applicability of the procedure and the damage modelling technique.

円孔またはボルト継手を有する直交異方性板の引張り強度

Laminate configurations of some composite plates for practical use can be considered to be quasi-orthotropic. In the present paper experimental results on tensile strength of laminates with loaded and unloaded circular holes are described. The plates are made of carbon fibre reinforced plastics and can be considered to be either quasi-isotropic or quasi-orthotropic. The experimental results are compared with the calculated first failure strength. The calculations are made by applying Lekhnitskii's stress expression for orthotropic plates with circular holes and Zhang and Ueng's approximate stress expression for orthotropic plates with pin-loaded holes. The calculated strength is much lower than the experimental one as expected. Some consideration about the discrepancy is given.

Stress Transfer in Single Fiber/ Resin Tensile Tests

Abstract Microscale (25 mm gauge length) “dogbone” resin specimens with single carbon fibers embedded through the length of the specimen have been studied as a method for determining the fiber-resin interphase strength. The specimens are pulled in tension until the fiber fragments to a critical length, lc . Evidence is presented here, based primarily on the relaxation of stress birefringence around the fiber fragment, that this test may not be an unambiguous measure of fiber-resin adhesion. Data obtained for various production lots of AS-4, AS-6, and IM-6 fibers indicate an increase in lcd with laminate tensile strength. Although there is theoretical justification for this correlation, it requires that the interphase shear strength is relatively constant. In those instances where interfacial adhesion was expected to be low, i.e., surface contamination or unsurface treated fiber, there was a significant increase in lc/d and usually a distinct difference in stress birefringence compared to “good” adhesion. ...

Reply by Authors to R. Prabhakaran

E comment by Professor Prabhakaran will be addressed in the order presented. 1) We acknowledge that interlaminar stresses are an important three-dimensional localized effect at the hole boundary. However, solutions require addressing the complete three-dimensional elasticity boundary value problem. No analytic solution to this extremely complex problem currently exists for general loadings surrounding an open hole in an arbitrary orthotropic laminate. Tang explains the complexity of this problem relative to open holes, and also provides an extensive reference list. The authors recognized that modeling all observed phenomenon would have required a three-dimensional, nonlinear, inelastic stress analysis. We chose a phenomenological approach to permit use of available and general two-dimensional, linear-elastic, closedform analysis in conjunction with known material failure criteria. The wisdom of our analytic approach and associated approximations was evaluated by correlating predictions with test data which we reported in our paper. l 2) Our paper demonstrates that the analytic procedure used, within acceptable engineering accuracy, predicts the effect of hole size on laminate tensile strength. Specimen width to diameter ratios were maintained constant. We question the general validity of Prabhakaran's comment concerning inherent size effect . . . of unnotched tensile strength with width. Prabhakaran arrives at this conclusion based on data obtained from specimens fabricated from E-glass fabric/epoxy. Nonlinear and inelastic mechanical behavior are oresent in glass-epoxy and initiate at low strains (.004 mm/mm) relative to final failure (.029 mm/mm). Glassepoxy mechanical behavior is not similar to graphite-epoxy behavior which exhibits relatively linear-elastic behavior to tensile failure. All laminate strength data were obtained from specimens loaded to failure in tension, lamina unnotched strength data were obtained from sandwich beam and rail-shear specimens. 3) The important differences between our analytic procedure and the two-parameter models are not those which Prabhakaran discusses. Our objective was to predict