Glass Plies Research Articles

Study of tensile‐tensile fatigue behavior of patch repaired carbon‐glass hybrid composite

AbstractAside from the numerous benefits of fiber‐reinforced composites, these materials are prone to impact damage, reducing structure's strength and stiffness. In this case, composite repair offers a unique and cost‐effective alternative for restoring structural integrity. In this work, post‐repair performance of the carbon‐glass hybrid composite is investigated in tensile‐tensile fatigue loading environments. To analyze repair performance, two distinct parent configurations (H1:G2C4G2 and H2: C2G4C2) and four patch configurations (Repaired1: CG3, Repaired2: C2G2, and Repaired3: C3G, Repaired4: G4) are considered. The digital image correlation approach and acoustic emission sensors are used to examine the specimens' damage behavior. First, fatigue tests are performed for drilled specimens, the H2 specimen dissipate more energy during fatigue cycles than the drilled H1 specimen due to the early damage initiation in the H2 specimen. The repaired specimens with the parent H1 laminate performed better than the parent H2 laminate. The Repaired4 configuration with H1 parent laminate sustained 300% higher cycles than the drilled H1 without final failure, which showed the highest fatigue life among all the repaired configurations. Patches with fewer glass plies outperformed all hybrid patches. The damage events recorded by acoustic emission sensors indicate that delamination damage considerably impacts fatigue life.Highlights Post‐repair fatigue behavior of carbon‐glass hybrid composite was examined. Effect of parent laminate stacking sequence and patch configuration was studied. Fatigue performance was analyzed using the damage mode and energy loss factor. Digital image correlation technique and acoustic emission sensors were utilized. Delamination damage showed a higher impact on the fatigue life of the sample.

Experimental study on full-scale glass roof panels with embedded laminated connections under the short-term and long-term loading

This experimental study covers a problematic of full-scale roof panels with four embedded laminated point connections under two types of loads - short-term loads on intact panels, and long-term uniform loads after the fracture of a thermally treated glass pane. Two types of panels consisting either of fully tempered, or heat strengthened glass plies in combination with float glass, were tested, and a specific type of Ethylene Vinyl Acetate foil was used as the interlayer. The first part of the study investigates short-term load bearing capacity of horizontally suspended panels. The load was applied in several loading and unloading cycles until the collapse of any connection. The second part of the study is focused on the residual load-bearing capacity of the roof panels after a partial failure, whereas a first step, the thermally treated glass plies were intentionally fractured. The long-term part of the experiment was performed within 65 days. During this period, the load was increasing until a collapse of any connection. In both types of experiment, a difference between specimens with fully tempered and heat strengthened glass was observed. In the short-term part of the experiment, the specimens with fully tempered glass failed in two steps and therefore, showed considerable post-failure load bearing capacity. On the other hand, the specimens with heat strengthened glass collapsed suddenly in one moment giving no post-failure capacity. In the long-term part of the experiment, the resistance of specimens with heat strengthened glass was higher than the resistance of specimens with fully tempered glass. Therefore, both types of panels might find its purpose in real applications if the needs of the structure are properly considered.

Post-Failure Behavior of Point-Fixing Laminated Glass Plates under Out-of-Plane Uniform Pressure

This paper presents the results of an experimental and numerical investigation of the mechanical response of undamaged and damaged 2-ply laminated glass plates. Two types of glass plies, thermally toughened and heat-strengthened, coupled with SentryGlas (SG) were considered. Laminated glass plates supported with articulated point fixing bolt under out-of-plane uniform pressure were investigated under four different damage configurations: (i) undamaged; (ii) partially damaged, with the bottom ply broken; (iii) partially damaged, over-flipping the specimen of mode II; (iv) both two glass plies broken, which was applicable for LG plates made by heat-strengthened glass. In the above four modes, the top ply is always subjected to compression while the bottom one is in tension. The different responses of each configuration (different glass types and damage modes) were discussed and compared in this study. In addition, numerical models were adopted to reproduce the experimental results. The influence of the hitting location and glass types on the mechanical behavior of LG plates was analyzed. The results showed that the contribution of the broken glass ply could not be disregarded in the evaluation of the global stiffness of partially damaged LG plates and their bearing capacity.

Experimental Analysis of the Post-Fracture Behaviour of Laminated Glass With Bolted Connections

Abstract Ensuring the sufficient residual resistance of glass structures after the failure of one glass ply to the failure of all the glass plies is an integral part of the design of glass structures. This paper presents an experimental study of bolted connections in laminated glass during three stages of a glass specimen: an intact glass specimen, a specimen with one ply of glass broken, and a specimen with both plies of glass broken. The effect of the type of glass was observed. The experiment proved that laminated glass made from thermally-toughened glass with bolted connections in its unfractured state has significantly higher resistance than laminated glass made from annealed glass. In a state of both plies of glass broken, the specimens made from annealed glass showed a higher residual resistance than specimens made from thermally toughened glass. The performance at this stage was also influenced by the temperature and loading speed. The expected strength of the glass was calculated on the basis of numerical models.

Review of the Main Mechanical Testing Methods for Interlayer Characterization in Laminated Glass

In the last decades, the use of structural glass has increased exponentially. The reliability of brittle structural glass elements is considerably improved if laminated glass elements are chosen because, in this case, a redistribution of internal forces is permitted once a limited breakage occurs. Thus, instead of monolithic glass, composite materials consisting of two or more glass plies bonded together using a polymeric film as an interlayer are used. In the event of glass failure, because of the chemical bond between the different materials, the adhesion to the interlayer prevents glass fragments from scattering. To design structural elements, the definition of the mechanical features of the interlayer is necessary. However, several standards and techniques can be applied, considering the characterization of either the interlayer itself or the laminated glass. The paper reviews the main existing methods and focuses on the standard suggested by the CEN/TS 19100:2021, analyzing in detail the effect of the different parameters involved. A numerical model is presented to account for the effect of the stress level, glass, and interlayer thickness. Although the standard leaves a certain degree of freedom in choosing those parameters, in some cases the results can differ.

Enhanced Delamination Tolerance Levels by Hybridizing Carbon Laminates with Glass Plies: Parametric Study

Laminated composites are extensively used in the aerospace industry and one of the key issues is delamination tolerance in these configurations during the operational phase. This paper demonstrates that hybridization is an effective strategy to achieve higher delamination tolerance sizes. For the above purpose, this paper presents a method to hybridize two different practical laminated carbon composite panels with glass fibers and also a parametric study to evaluate the influence of various hybrid laminate parameters on the delamination tolerance. Geometrical non-linear finite element analysis is carried out on three-dimensional models of delaminated non-hybrid and hybrid composite laminates. The mode I Strain Energy Release Rate (SERR) is estimated using Modified Virtual Crack Closure Integral (MVCCI). The SERR components are compared for the hybrid and the non-hybrid laminates. It is demonstrated that an appropriate hybridization with glass plies in between a few top and bottom carbon layers enhances delamination tolerance levels without significantly affecting the stiffness of the laminate.

Mechanical Behavior of Hybrid Laminated Nano Composite Containing Equal Numbers of Glass and Carbon Fiber Plies

Hybrid fiber reinforced polymer with nanofiller composite was introduced into a lot of industries due to its extreme mechanical properties in comparison with non-hybrid material. In this investigation, cross and quasi-fiber laminated epoxy composites with and without nano Al2O3 were fabricated using Vacuum Assisted Resine Infusion Method and Ultrasonic Dual Mixing Method. In general, the results of mechanical properties indicated that the addition of 2% nano Al2O3 enhances the tensile and flexural properties. Cross number 2 with nano Al2O3 laminate had the maximum tensile strength 628 MPa and maximum tensile strain of 1.74%, while cross number 1 with nano Al2O3 laminate had the maximum tensile modulus of 37.756 GPa in the cross group. In the quasi group, quasi number 2 with nano Al2O3 had the maximum tensile strength, maximum tensile strain, and maximum tensile modulus, equal to 294 MPa, 1.98%, and 16.409 GPa, respectively. Regarding the flexural properties, cross number 1 with nano Al2O3 laminate had a maximum flexural strength of 708.2 MPa and maximum flexural strain of 2.027%, while cross number 2 with nano Al2O3 laminate had a maximum flexural modulus of 38.73 GPa in the cross group. On the other hand, quasi number 1 with nano Al2O3 laminate had the maximum flexural strength, maximum flexural strain, and maximum flexural modulus equal to 596 MPa, 2.424%, and 29.2 GPa, respectively in the quasi group. The internal structures of the failure laminated composites through scanning electronic microscopy confirm that the adhesion between fibers and matrix is good.

The Dynamic Behaviour of Symmetrical Laminated Nano-composite Containing Equal Numbers of Glass and Carbon Fibre Layers

Fibre-reinforced polymer composite has many uses in structural components that required high strength, stiffness, and damping capacity. Cross and quasi-laminated epoxy composites with and without nano Al2O3 were used in this investigation to determine flexural modulus, natural frequency, damping ratio, and mode shapes by using analytical, experimental, and numerical (ANSYS) methods. It was demonstrated that adding 2 % nano Al2O3 improved the flexural modulus and the damping ratio while decreased the natural frequency. Cross number 2 and quasi number 2 had the highest natural frequency for cross and quasi laminate groups which are equal to 23.5 Hz and 20.25 Hz experimentally, respectively. On the other hand, the higher damping ratio was achieved for cross number 1 with nano Al2O3 and quasi number 2 with nano Al2O3 for both cross and quasi laminates, which are equal to 0.707 % and 0.693 %, respectively. The flexural modulus and damping ratio are inversely related to each other. However, the novelty in this article is that by adding two glass plies at the outer surface of quasi group laminate the flexural modulus, natural frequency, and damping ratio are increased simultaneously, as in the configurations quasi number 2 and quasi number 2 with nano Al2O3 in comparison with quasi number 1 and quasi number 1 with nano Al2O3.

A constrained solid-shell model for the geometric nonlinear finite-element analysis of laminates with alternating stiff/soft layers. Applications to laminated glass

Solid-shell models are developed for the geometrically nonlinear analysis of multi-layered composite structures made of alternating layers with large difference in material properties. Exemplificative applications are presented for laminated glass, in which a number of stiff plies of glass are permanently shear-coupled by soft interlayers. The sectional warping due to significant transverse shear strains in the soft layers makes theories of laminated plates based on the plane-section hypothesis unreliable. The proposed approach is based on a geometrically exact solid-shell finite element model with one element per layer in the thickness direction, as alternative to solid discretization. The element approximation is based on the displacement nodal values at the top and bottom surfaces of the layers, with a natural C0 continuity. An alternative solid-shell model with fewer parameters is derived imposing the equal finite rotation of the stiff layers at each surface point by a local rotation-free re-parametrization of the nodal displacements and enforcing the plane stress condition. The approach permits an easy coupling with a fully solid discretization, e.g. to model connections, and is based on a simple strain measure quadratic in the displacement unknowns and suitable for finite strains. Extensive numerical examples for laminated glass plates and curved shells susceptible to large deflections and buckling are provided, comparing the results with those from a fully solid approach.

Evaluation and Comparison of Fracture Toughness of Glass Fibre Reinforce Composites

The study of the behaviour of a broken structure or component under service conditions is known as fracture mechanics. Impurities, uneven curing, holes and notches are all sources of fractures. Cracks are common local discontinuities in materials caused by a variety of factors. Such discontinuities cause the structure's rigidity and consequently load bearing capability to deteriorate. It is known that for the crack to propagate, the stress in the locale of the crack tip should reach the critical value. Once stress level is critical, the crack propagates and leads to failure of the structure. A segment of the crack is divided into three modes namely Mode I (Opening mode), Mode II (sliding mode), Mode III (tearing mode). The current study presents a computational and experimental study on fractography and notch sensitivity evaluation in glass-fiber-reinforced-laminate under quasi-static load. For both numerical and experimental damage assessments, three volume fractions of glass and resin plies (50/50, 60/40, and 70/30) have been used. The fracture toughness investigation was carried out in accordance with ASTM standards, utilising a universal testing equipment. The numerical study is conducted out using the J-integral approach. The fracture toughness increases with resin content and is determined by the ductility of the plastic zone surrounding the crack tip. Within an acceptable range, the numerical findings are equivalent to the experimental values. When compared to the other modes, Mode 1 is the fatal. The mode I fracture toughness of several materials is evaluated experimentally and compared in this study.

Numerical analysis of mixed-mode I+II fracture behavior of automotive PVB laminated glass using a novel beam-type test specimen

Laminated glass is a composite structure consisting of a polymeric interlayer (e.g., polyvinyl butyral PVB) sandwiched between two glass plies. Due to the increasing use of laminated glass (LG) in advanced industries such as automotive sectors, it is of much importance to investigate the fracture behavior of such structures. One of the most critical steps in outlining the fracture behavior of laminated glass is the accurate determination of the fracture energy of the interlayer, usually, polyvinyl butyral (PVB), which is obtained from experimental methods. So far, various laboratory samples have been presented to measure the fracture energy of laminated glass, each of which has its advantages and limitations. In this paper, a new loading setup is proposed for the determination of mixed-mode I/II fracture energy in a rectangular-shape laboratory sample of laminated glass. The loading setup consists of a rectangular beam under a four-point bending which has been analyzed by the commercial ABAQUS software package. By utilizing this specimen, the fracture energy of the combined modes from pure mode I to pure mode II in the PVB interlayer can be measured. The proposed geometry here is simpler than other available geometries in the literature and also it does not require a complex loading mechanism. The effects of crack length ratio and also the support distance on fracture parameters such as and are well investigated.

Water absorption behavior of the woven bamboo fabric polypropylene-based composites and their hybrids with glass

The high prone behavior towards water absorption is considered as a major weakness of natural based-fiber composites or bio-composites. These composites can be susceptible to considerable water absorbed due to hydrophilic nature of bamboo fiber, which may affect to degradation of their strength and stiffness performances. The effect of the hybridization is investigated with the study of water immersion at 23 °C and 60 °C, for a period of 70 days. It was shown that the composite’s absorption behavior demonstrated the kinetics behavior and classification proposed by Fick’s theory. There was a 142 % increase in the diffusion coefficients of samples immersed at 60 °C compared to those at 23 °C for BPP composites. The water absorption of BPP composites at 23 °C after 1680 h was approximate of 14.6 %, with the absorption was quite rapid initially, reaching almost 13.01 % after about 720 h. For the hybrid composites of 30B:20G, 20B:35G and 10B:45G for water absorption at 23 °C was reaching almost 10.56 %, 7.30 %, and 2.81 % respectively after 720 h. Furthermore, the composites approached equilibrium faster at 60 °C than at 23 °C. The absorption rate was significantly higher at 60 °C, with 80 % of the total absorption in the first 14 days, while the BPP composites at the immersion of 23 °C, reached equilibrium in the first 30 days. Similar behavior was also observed for the hybrid composites, reached almost 80 % of the total absorption in the first 7 days, when compared with 20 days for the hybrid composites. The presence of external plies of glass effectively decelerates water diffusion into the bamboo polypropylene (BPP) composites. The findings denote a significant observation in which, by substituting few layers of glass with woven-based bamboo in glass-polypropylene composites, offering to a hybrid concept to be possible for developing an alternative, excellent and better performance of light-weight composite.

A Simple Model for Inflexed Multilayered Laminated Glass Beams Based on Refined Zig-Zag Theory

Abstract Laminated glass is a composite made of glass plies sandwiching polymeric interlayers, permanently bonded with a process at high pressure and temperature in autoclave. Within the quasi-elastic approximation, according to which the polymer is linear elastic material whose elastic modulus parametrically depends upon time and environmental temperature, we present a model for inflexed laminated-glass beams in the pre-glass-breakage phase. The approach relies on a modified version of the refined zig-zag theory for composites, in which the glass plies are treated as Euler–Bernoulli beams, whereas the interlayers can only provide a shear-stiffness contribution to the coupling of the glass plies. The kinematic description is greatly simplified and the governing equations can be solved analytically, for laminated packages of any type, when the beam is statically determined. A finite element implementation is proposed for the most general cases. The convergence analysis for the numerical approach and the comparison with the analytical solution in benchmark problems demonstrate the efficiency of the proposed method.

Flexural analysis of hemp, kenaf and glass fibre-reinforced polyester resin

Abstract Natural fibres have a high potential to replace synthetic fibres such as glass in a variety of applications. However, natural fibre-reinforced composites still have some limitations with respect to the mechanical performance especially in high load bearing capabilities. The hybridization of natural fibres with synthetic fibres in the same matrix has proven to create a balancing effect and enhanced the composites performance. Besides that, fibre architectures that include fibres continuity, fibres orientation, fibres arrangement and fibres interlocking are also considered to enhance the overall performance of the composites. In this study, the hemp mat, kenaf mat and glass chopped strand mat were hybridised with woven glass fibres, respectively in polyester resin to form 12 systems of the composites. The hybridization effects of different fibre core material, fibre core thickness and fibre arrangement on flexural response were investigated according to ASTM D7264. The results indicated that hybrid CSM glass/woven glass composite showed the highest flexural strength and modulus compared to hemp/woven glass and kenaf/woven glass composites, with about 377.15 ± 48.41 MPa and 16.74 ± 7.15 GPa. Among natural fibres, kenaf fibre (2WG/K/2WG) composite showed better flexural properties compared to hemp fibre (2WG/H/2WG) composite. 2WG/2G/2WG composites with two plies of CSM glass showed maximum flexural properties. As for hemp/woven glass and kenaf/glass hybrid composites, the flexural properties reached a maximum value in system arrangement of (2:1:2) but it reduced in the system arrangement of (2:2:2) and (2:4:2). On the evaluation effect of fibre arrangement, hemp, kenaf and glass mat used as core (arrange in the middle; (2:2:2)) showed higher flexural properties as compared to the use as skin (arrange in outer; (1:4:1)). (2WG/2K/2WG) showed better flexural properties than (2WG/2H/2WG) as the core, while (H/4WG/H) showed better flexural properties than (K/4WG/K) as skin.

Comparison of Behaviour of Laminated Banister Panels with Embedded Connections

Glass became a very popular building material in recent decades. Modern architecture often works with glass facades, roofs, banisters or columns. However, using glass elements in structures may be problematic due to glass elements connections. The connection must bear all stresses arising during the lifetime period and meet high aesthetical standards at the same time. Various bolted and adhesive connections were developed in order to achieve as transparent look as possible. The embedded laminated connection combines mechanical and adhesive fixing systems. The ongoing research at the Faculty of Civil Engineering of the CTU in Prague is focused on the characteristics of this type of connection. Within this research, two sets of real-scale laminated banister panels with the embedded connection were tested. The first set included the samples consisting of two 8 mm glass plies bonded with two layers of an EVA foil. The second set of samples consisted of one 10 mm glass ply and one 6 mm glass ply also bonded with two layers of an EVA foil. There was one pair of embedded steel countersunk bolts with HDPE liners in each of the lower corners. A short-term vertical load was applied on the samples. During the experiment, stresses and deflections in several points were measured. The experiments showed the collapse mode and a short-term resistance of a laminated glass panel with two sets of embedded point connections under a vertical load. It also allowed comparing the behaviour and resistance of two panels of identical total thickness differing in glass ply compositions.

The Conjugate Beam Effective Thickness Method

The structural performance of laminated glass is strongly dependent on the shear coupling offered by the interlayer between the bounding layered and monolithic limits of the glass plies. The most common simplified design approach consists of defining the effective thickness, i.e., the thickness of a monolithic section with equivalent flexural section properties. The Enhanced Effective Thickness (EET) method has been verified to estimate deflection in laminated glass for a range of load and boundary conditions for two-, three-, and multi-ply beams; however, for some static schemes, the EET method is less accurate for predicting stress. The recently proposed Conjugate Beam Effective Thickness (CBET) method, initially developed for cantilevered laminated glass balustrade applications, accounts for the relative displacement of glass plies across the interlayer for a range of loads and statically determinate boundary conditions. In this paper, the CBET method is extended to the evaluation of two-ply simply supported beams under concentrated, uniformly, and tapered distributed out-of-plane loads. Predicted deflection- and stress-effective thickness obtained from effective thickness methods is compared with finite element model results in illustrative examples, demonstrating improved accuracy. Closed-form formulas are summarized in tables to facilitate the practical application of the CBET method in the design practice.

Effect of patch-parent stacking sequence and patch stiffness on the tensile behaviour of the patch repaired carbon-glass hybrid composite

In this work tensile behaviour of the patch repaired carbon-glass woven hybrid composites was investigated with patches of different stiffnesses and stacking sequences with the aid of digital image correlation and acoustic emission. Two parent hybrid laminates were repaired with eight patches constituting carbon and glass plies. The damage modes are studied to understand their effect on load recovery. The least stiff patch combination with parent laminate having exterior ply as the glass ply exhibited 24.6% higher load than the drilled specimen. The patches with glass ply facing the parent laminate showed better recovery for the same patch stiffness.

Post repair high velocity impact behaviour of carbon-glass hybrid composite: Experimental and numerical study

In this work post repair high velocity impact behaviour of carbon-glass hybrid composite was investigated. Two parent hybrid laminates(H1:G2C4G2 and H2:C2G4C2), two double sided patches (P1: G2C2 and P2: C2G2) and two single sided patches (P3: G2C4G2 and P4: C2G4C2)) were used in this study. The velocities in the range of 80-120 m/s were considered for this study. The effect of patch type and stacking sequence of patch plies on the impact resistance were studied. A 3D finite element model based on continuum damage mechanics approach was also developed to further understand the effect of the ratio of glass to carbon plies in a patch. The Hou damage initiation criteria and strain based damage evolution criteria were incorporated in the proposed numerical model. Overall, the P3 patch repair specimen performed better than all patch repaired specimens and the P2 patch repair specimen performed better than all double side patch repaired specimens. The P3 patch repaired specimen showed an 8% higher ballistic limit than the P2 repaired specimen patch. It was also observed that number of glass plies in the patch govern the damage development in the specimen and residual velocity of projectile.

Post-failure behavior of 2-ply laminated glass plates with different interlayers

Modern design codes, such as the new Eurocode on the design of structural glass components, consider the prediction of the post-failure behavior of these elements of paramount importance for a proper and safe design. In this view, an experimental investigation is presented in the paper, on the mechanical response of undamaged and damaged 2-ply Laminated Glass (LG) under quasi-static loads, with different interlayers, namely polyvinyl butyral (PVB), SentryGlas (SG) and a plasticized version of PVB, Saflex DG41 (DG41). Firstly, undamaged specimens (UDLG) were tested in simply supported configuration (configuration 0) with a vertical load in the middle increased up to the failure of the bottom glass ply. damaged LG specimens (PDLG) were then tested into two different configurations: configuration I, with broken ply below (bottom ply) and configuration II, with broken ply above (top ply). All the presented tests were performed under displacement control. For both configurations, the interlayers influence on the post-breakage behavior was discussed. It is underlined that the global response of the two configurations was completely different: configuration II, which was characterized by a deformed shape opposite to the load direction, showed a good residual stiffness and reached high failure loads. On the contrary, in configuration I, the response was characterized by a low stiffness and load carrying capacity. In addition, also the influence of different glass types was discussed, focusing attention on tempered and toughened glass. The results showed that the contribution of the fractured layer cannot be disregarded in the evaluation of the global stiffness of a PDLG and its contribution is strictly related to the interlayer and glass typologies.

A fractional viscoelastic model for laminated glass sandwich plates under blast actions

A model is proposed to evaluate the effects of explosions on laminated glass plates, made of glass plies bonded by thin polymeric interlayers, in the pre-glass-breakage phase. The novelty consists in the description of the viscoelastic properties of the interlayer, based on fractional calculus. This has noteworthy advantages because the relaxation function of most commercial polymers can be well approximated by power laws in the time interval of interest: in the fractional approach, this trend can be directly described by only two material parameters, whereas the traditional Prony series requires many more coefficients to be calibrated. Modelling of the plate is layerwise and the coupling with an elastic supporting back structure is considered. The glass plies are Kirchhoff–Love plates, whereas the impinging pressure from the explosion follows Friedlander equation. The governing equations, found via Hamilton’s principle, are solved à la Galerkin through a spatial expansion in Fourier series and a step-by-step integration in time using the Grünwald–Letnikov operators. Numerical experiments aim at describing how the fractional parameters of the interlayer, as well the compliance/mass of the back structure, affect the stress and deflection of the laminated plate. Comparisons are made with the commonly used quasi-elastic approximation, which considers the interlayer as linear elastic. The results show that the viscosity of the interlayer cannot in general be neglected and how a compliant back structure can help to safeguard the glass, although its displacement may exceed the serviceability limits. The optimal design shall thus represent a compromise between different effects: despite its limitation, the proposed model can represent a tool to make a correct choice.