Experimental characterization and computational simulations of the low‐velocity impact behaviour of polypropylene

The objective of this work is to validate predictive models for the simulation of the mechanical response of polypropylene undergoing impact situations. The transferability of material parameters deduced from a particular loading scenario (uniaxial loading) to a different loading situation (multiaxial loading) was studied. The material was modelled with a modified viscoplastic phenomenological model based on the G'Sell–Jonas equation. To perform the numerical simulations, a user‐material subroutine (VUMAT) was implemented in the ABAQUS/explicit finite element code. Constitutive parameters for the model were determined from isostrain rate uniaxial tensile impact test data using an inverse calibration technique. In addition, falling‐weight low‐energy impact tests were performed on disc‐shaped specimens at velocities in the range 0.7 to 3.13 m s^?1. The model predictions were evaluated by comparison of the experimental and finite element response of the falling‐weight impact tests. The G'Sell–Jonas model showed much better predictability than classical elastoplasticity models. It also showed excellent agreement with experimental curves, provided stress‐whitening damage observed experimentally was accounted for in the model using an element failure criterion. © 2013 Society of Chemical Industry     

Effect of interlaminar toughness on the low‐velocity impact damage in composite laminates

Based on the continuum damage mechanics (CDM) and the cohesive zone model (CZM), a numerical analysis method for the evaluation of damage in composite laminates under low‐velocity impact is proposed. The intraply damage including matrix crack and fiber fracture is represented by the CDM which takes into account the progressive failure behavior in the ply, using the damage variable to describe the intraply damage state. The delamination is characterized by a special contact law including the CZM which takes into account the normal crack and the tangential slip. The effect of the interlaminar toughness on the impact damage is investigated, which is as yet seldom discussed in detail. The results reveal that as the interlaminar fracture toughness enhances, the delamination area and the dissipated energy caused by delamination decrease. The contribution of normal crack and tangential slip to delamination is evaluated numerically, and the later one is the dominant delamination type during the impact process. Meanwhile, the numerical prediction has a good agreement with the experimental results. The study is helpful for the optimal design and application of composite laminates, especially for the design of interlaminar toughness according to certain requirements. POLYM. COMPOS. 37:1085–1092, 2016. © 2014 Society of Plastics Engineers     

Fabrication,characterization and low‐velocity impact testing of hybrid sandwich composites with polyurethane/layered silicate foam cores

A series of nanophased hybrid sandwich composites based on polyurethane/montmorillonite (PU/MMT) has been fabricated and characterized. Polyaddition reaction of the polyol premix with 4,4′‐diphenylmethane diisocyanate was applied to obtain nanophased PU foams, which were then used for fabrication of sandwich panels. It has been found that the incorporation of MMT resulted in higher number of PU cells with smaller dimensions and higher anisotropy index (cross sections RI and RII). The obtained materials exhibited improved parameters in terms of thermal insulation properties. The results also show that nanophased sandwich structures are capable of withstanding higher peak loads than those made of neat PU foam cores when subject to low‐velocity impact despite their lower density than that of neat PU foams. This is especially significant for multi‐impact recurrences within the threshold loads and energies studied. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Effect of geometry and loading fractions on energy absorbing properties of fiberglass polymer composite under quasi‐static and low‐velocity impact loadings

The focus of this study is to experimentally investigate the mechanical properties of fiberglass reinforced composite with various aspect ratios and loading fractions in the quasi‐static and low‐velocity impact loading conditions. In this study, short fiberglass reinforced polycarbonate composite materials were fabricated via a solution mixing method and characterized for their tensile properties by varying both fiberglass loading fraction and aspect ratio. The tensile properties including tensile toughness of the fiberglass reinforced composites were characterized and compared. It was observed in this study that the toughness of the composite was dramatically improved whereas the tensile strength and Young's modulus were moderately enhanced over the neat polymer, which were measured to be only up to 15% and 70% increase, respectively. The low‐velocity impact behaviors of the fiberglass composites were also investigated and compared to the tensile toughness of the corresponding composites. Besides, the effect of thickness on their low‐velocity impact properties was investigated. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 40821.     

A new numerical model for the analysis on low‐velocity impact damage evolution of carbon fiber reinforced resin composites

A new numerical simulation method was proposed to predict the mechanical behavior of carbon fiber reinforced resin composites under low‐velocity impact load. The impact damage evolution can be characterized in the form of energy dissipation which can be calculated through the new numerical model. The evolution mechanism of delamination was analyzed through distinguishing between the normal induced delamination and tangential slip induced delamination. The drop weight tests were conducted on composite laminates with five kinds of stacking sequence. Experimental analysis was also presented in this article. The damage area and distribution was investigated through ultrasonic C‐scan. The prediction had a good agreement with the experimental results through the comparison of impact response. © 2016 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017 , 134, 44374.     

High velocity impact behavior of GRP panels containing coarse‐sized sand filler

Ballistic performance of glass reinforced plastic (GRP) composite plates containing coarse sized sand filler was investigated as an attempt towards developing a low cost armored system. In all, 10 different types of plates from 4 to 12 layers of E‐glass chopped strand mat reinforced polyester resin containing 0, 10, and 20% of 600‐ to 700‐μm sized sand filler were tested. A smooth barrel gas gun was used to conduct high velocity tests in the range of 70–185 m/s. Results indicated higher ballistic performance for GRP plates with sand filler in terms of higher ballistic limits (velocity at which at least 50% of samples were partially or fully penetrated the target plates with zero residual velocity), particularly for plates with highest sand filler loadings. Energy absorption associated with these specimens also showed higher performance. Delamination was identified as dominant failure mode, in particular for thicker specimens with highest sand filler loading. Specific energy absorption per weight per unit area for the composite plates indicated diminishing effectiveness with increase in sand filler loading, thereby limiting its possible application to armored system for stationary objects only. POLYM. COMPOS., 2008. © 2008 Society of Plastics Engineers     

CFRP laminates under low‐velocity impact conditions: Influence of matrix and temperature

In this work, carbon fiber‐reinforced composites (CFRP), respectively, based on a vynilester and epoxy resin were loaded under low‐velocity impact condition to highlight the influences of different matrices and temperature on their dynamic response. In particular, measurements were performed at room and the low temperature of ?25°C on samples simply supported by air to exactly simulate the incidental impact during the structure service and having the same thickness. Impact tests were carried out at penetration to obtain the complete load–displacement curve and to measure the penetration energy, and at different energy levels, 5, 10, and 20 J, to investigate the influence of the matrix on the damage start and propagation. After the impact tests, the specimens were nondestructively investigated by the ultrasound technique to measure the delamination. The interesting results obtained on carbon fiber laminates impacted at room and lower temperature are here reported and compared. In general, better behavior was noted for vinyl ester‐based composites, extensively used in the naval field, thanks to their low absorption for humidity. POLYM. ENG. SCI., 59:2429–2437, 2019. © 2019 Society of Plastics Engineers     

High-velocity impact loading in honeycomb sandwich panels reinforced with polymer foam: a numerical approach study

The employment of lightweight structures is one of the most important goals in various industries. The lightweight sandwich panel is an excellent energy absorber and also a perfect way for decreasing the risk of impact. In this paper, a numerical study of high-velocity impact on honeycomb sandwich panels reinforced with polymer foam was performed. The results of numerical simulation are compared with the experimental findings. The numerical modeling of high-velocity penetration process was carried out using nonlinear explicit finite-element code, LS-DYNA. The aluminum honeycomb structure, unfilled honeycomb sandwich panel, and the sandwich panels filled with three types of polyurethane foam (foam 1: 56.94, foam 2: 108.65, and foam 3: 137.13 kg/m³) were investigated to demonstrate damage modes, ballistic limit velocity, absorbed energy, and specific energy absorption (SEA) capacity. The numerical ballistic limit velocity of sandwich panels, filled with three types of foam, was more than that of a bare honeycomb core and unfilled sandwich panel. In addition, the numerical results showed that the sandwich panel filled with the highest density foam could increase the strength of sandwich panel and the numerical specific energy absorption of this structure was 23% more than that of unfilled. Finally, the numerical results were in good agreement with experimental findings.

     

Characterizations of basalt unsaturated polyester laminates under static three‐point bending and low‐velocity impact loadings

This paper reports the responses of basalt unsaturated polyester laminates under static three‐point bending loading and low‐velocity impact. Three kinds of composite materials, unidirectional (0°), cross‐ply (0°/90°) and woven laminates were considered. The laminates were fabricated by layup process and hot pressed under pressure. Static three‐point bending tests and low‐velocity impact tests were conducted to obtain the force–deflection, force–time, deflection–time, velocity–time, and energy–time curves. The results showed that unidirectional (0°) laminates carried more load during static loading, but in the event of dynamic loading, cross‐ply, and woven laminates were more superior. It was observed that the failure of 0° laminates was along the fiber direction while for cross‐ply and woven, the damage was localized, around the impacted locations. From the different combinations of unidirectional (0°), cross‐ply (0°/90°) and woven lamina, the impact behaviors could be optimized with the lowest area density. POLYM. COMPOS., 35:2203–2213, 2014. © 2014 Society of Plastics Engineers     

Processing-properties relationship of sandwich panels with polypropylene-core and polypropylene-matrix composite skins

This paper reports on the development and the optimization of a thermoforming process (compression molding) for thermoplastic sandwich panels. The skins of the panels are fabricated from polypropylene (PP)/continuous glass fibers dry prepregs in the form of a commingled fabric. The use of two different types of core material has been used, a PP foam and a PP honeycomb. Additionally, two alternative methods for the thermoforming process have been analyzed, using either a one-stage or a two-stage process. In the one-step process, skin molding and skin-core bonding are carried out simultaneously. In the two-stage process, the skins are first thermoformed and then bonded to the core as the second stage. The influence of the selected process parameters on the mechanical properties of the panels has been experimentally investigated, leading to the identification of the preferred processing conditions. Polym. Compos. 25:307–318, 2004. © 2004 Society of Plastics Engineers.     

Insulation failure of lightweight composite sandwich panels exposed to flame

A critical consideration for the serviceability of composite sandwich panels is their thermal behaviour during fire incidents. This research aims to observe the thermal performance and investigate the insulation failure of the lightweight concrete sandwich panels (LCSPs) in non-load bearing wall systems. Six standard one-sided coupling fire tests on LCSPs in accordance with Australian standard AS 1530.4 were conducted via an electrical furnace; measured by thermocouples and a thermal camera, to assess the insulation capacity and their behaviour during fire events. The results indicated that the sandwich panels have insulation capacity for 75 to 110 minutes depending on the thickness and density. The bowing of the panels due to the expansion of the exposed steel shield and the consequent de-bonding and cracking of concrete was one of the primary reasons of insulation failure. Additionally, this bowing led to the opening of the joints between the panels, which could allow the heat flows towards the unexposed surface. Moreover, the propagation of accelerated drying shrinkage cracks in the restrained concrete core was another reason for the failure. Lastly, the results suggested the benefits of increasing the thickness and density on thermal performance and insulation failure of the composite sandwich panels.     

The comparison of low‐velocity impact resistance of aluminum/carbon and glass fiber metal laminates

This article presents the low‐velocity impact response of fiber metal laminates, based on aluminum with a polymer composite, reinforced with carbon and glass fibers. The influence of fiber orientations as well as analysis of load‐time history, damage area and damage depth in relation to different energy levels is presented and discussed. The obtained results made it possible to determine characteristic points, which may be responsible for particular stages of the laminate structure degradation process: local microcracks and delaminations, leading to a decrease in the stiffness of the laminate, as well as further damage represented by laminate cracks and its perforation. The damage mechanism of fiber metal laminates is rather complex. In case of carbon fiber laminates, a higher tendency to perforation was observed in comparison to laminates containing glass fibers. Delaminations in composite interlayers and at the metal/composite interface constitute a significant damage form of fiber metal laminates resulting from dynamic loads. Fiber metal laminates with glass fibers absorb energy mainly through plastic deformation as well as through delamination initiation and propagation, whereas laminates containing carbon fibers absorb energy for penetration and perforation of the laminate. POLYM. COMPOS. 37:1056–1063, 2016. © 2014 Society of Plastics Engineers     

Buckling of hybrid laminated composite sandwich panels with transversely flexible cores

Abstract

The structural performance of sandwich panels made with hybrid laminated faces and a transversely flexible core can be optimised by varying the mechanical and geometrical parameters characterising both the faces and the core, taking into account also the whole cost. In particular the hybridisation technique applied to the faces seems to be a very attractive solution, giving an improvement from both a mechanical and economical point of view. However, because of the out of plane flexibility of the core and the great slenderness of these structures, instability problems assume a relevant role from a static point of view, becoming a complex phenomenon as well. In this paper a modified first order shear deformation theory has been used, which treats the displacement field of the sandwich panels as a combination of different buckling modes. Buckling loads are finally obtained as a solution of an eigenvalue problem by means of an energetic algorithm solved by the Rayleigh-Ritz method. The influence of mechanical and geometrical parameters, characterising the composite laminated faces and the core, on buckling phenomena were investigated for different in plane load conditions. A numerical FEM approach was also employed; comparisons between FEM and analytical results, in which some key parameters were varied, show the effectiveness of the analytical model.     

Low‐velocity impact response in composite plates embedding shape memory alloy wires

In this work, the behavior of hybrid composite plates, embedding superelastic shape memory alloy (SMA) wires, subjected to low‐velocity impacts was studied. The impact experiments were performed on glass reinforced thermoset composite plates containing 1% by volume of superelastic thin wires (0.1 mm of diameter) of a SMA. The specimens were impacted with instrumented drop weight impact equipment: different dropping heights were used to attain impact energies from 1 to 500 J. The shape and size of damaged area were analyzed using two nondestructive inspection methods: (1) light scattering under back illumination was used to observe minor damages such as matrix cracks and fiber matrix debonding and (2) the size and shape of large damages such as delaminations were evaluated by infrared thermography. POLYM. COMPOS., 2012. © 2012 Society of Plastics Engineers     

Moisture absorption in foam‐cored composite sandwich structures

The hygroscopic behavior of sandwich structures composed of E‐glass/polyester face sheets bonded to a PVC foam core exposed to 95% relative humidity and immersed in sea‐water is examined herein. Moisture uptake was monitored for 11 months yielding absorption curves for samples of polyester resin, laminated composites, PVC foam core, and a sandwich structure. The coefficients of diffusion and moisture saturation values extracted from the curves are significantly greater for the water immersed condition than for the exposed to elevated moisture one, and point to the foam core as the most absorbing material in the sandwich structure. The measured absorption curves are compared to a diffusion model which employs the calculated coefficient of diffusion, showing good agreement. POLYM. COMPOS., 2010. © 2009 Society of Plastics Engineers     

Direct numerical simulations of dynamic gas‐solid suspensions

Direct numerical simulation results for gas flow through dynamic suspensions of spherical particles is reported. The simulations are performed using an immersed boundary method, with careful correction for the grid resolution effect. The flow systems we have studied vary with mean flow Reynolds number, solids volume fraction, as well as particle/gas density ratio. On the basis of the simulation results, the effect of particle mobility on the gas‐solid drag force is analyzed and introduced into the existing drag correlation that was derived from simulations of stationary particles. This mobility effect is characterized by the granular temperature, which is a result of the particle velocity fluctuation. The modified drag correlation is considered so‐far the most accurate expression for the interphase momentum exchange in computational fluid dynamics models, in which the gas‐solid interactions are not directly resolved. © 2016 American Institute of Chemical Engineers AIChE J, 62: 1958–1969, 2016     

Low‐velocity impact of nanocomposite and polymer plates

Nanocomposites are more widely studied today because of higher stiffness, decreased permeability, thermal stability, and many other properties superior to those of regular polymers. However, manufacturers are concerned about implementing nanocomposites because of their lower impact properties with respect to the base polymer. This study focused on low‐velocity impact tests of a thermoplastic olefin by itself and with 5 wt % nanoclay. The impact tests were conducted at ?40, 23.9, and 65.6°C until the polymer and nanocomposite plates experienced complete striker penetration. The force–time and force–deflection responses obtained from the impact testing provided a means of comparing the impact performances of the two materials. © 2005 Wiley Periodicals, Inc. J Appl Polym Sci 96: 2309–2315, 2005     

Behavior of sandwich structures and spaced plates subjected to high‐velocity impacts

This work evaluates the behavior of sandwich and spaced plates subjected to high‐velocity impacts. The sandwich structures were made of glass/polyester face‐sheet and a PVC foam core. The spaced plates were made of two plates of the same material of the sandwich face‐sheet at a distance equal to the core thickness. The residual velocity, the ballistic limit, and the damage area were selected to compare the response of both structures. The residual velocity and ballistic limit was very similar in both cases. Nevertheless, the damage area of sandwich structures and spaced plates differed due to the dissimilar properties between the sandwich core and the air inside of the spaced plates. An analytical model, based on energy criteria, was applied to estimate the residual velocity of the projectile, the absorbed energy by each face‐sheet, and the ballistic limit in the spaced plates. POLYM. COMPOS., 2011. © 2010 Society of Plastics Engineers     

Development and characterization of an all‐olefin thermoplastic sandwich composite system

In this investigation an all‐olefin thermoplastic sandwich system was developed and characterized. Commingled glass fiber polypropylene (PP) composite was used as skin and HDPE (PE) foam with closed cells as core. Infra‐red heating was used for melting the surfaces of the substrates for surface fusion bonding with a cold press. Two tie layer films, viz. ethylene‐propylene copolymer (EPC) and HDPE/elastomer blend, were used as hot melt adhesives for bonding the substrates. Single lap shear joints were prepared from PP composite and PE foam adherends with a bonding area of 25.4 mm × 25.4 mm to determine the interface strength. EPC tie layer provided higher bond strength (27.4 kg/cm²) to the all‐olefin sandwich system than HDPE/elastomer blend based one (19.7 kg/cm²). For EPC tie layer based sandwiches, a mixed mode a failure was observed in the failed lap shear samples; about 40% is cohesive failure through tie layer, and the rest of failure was adhesive either at PP composite or PE surfaces. Environmental scanning electron micrographs (ESEM) reveal that in the process of surface fusion bonding, PE foam cells in the vicinity of 0.80 mm interphase area were coalesced with high temperature and pressure. No macro level penetration of tie layer melt front into foam cells was observed. As the surface morphology of foam was altered on account of IR surface heating and the PP composite bonding side had a resin‐rich layer, the bonding situation was closer to that between two polymer film surface.     

A new improved high‐order theory for analysis of free vibration of sandwich panels

A new improved high‐order theory is presented to investigate the dynamic behavior of sandwich panels with flexible core. Shear deformation theory is used for the face sheets, whereas the three‐dimensional elasticity theory is used for the core. Displacements in the core are assumed as polynomial with unknown coefficients. Inertia forces, moments of inertia and shear deformations in the core, and the face sheets are taken into consideration. Unlike the previous improved theory, the in‐plane normal and shear stresses in the core are considered. The governing equations and the boundary conditions are derived by Hamilton's principle. Closed form solution is achieved using the Navier method and solving the eigenvalues. The numerical results of present analysis compared with the available results in the literature. It indicates that the present new modified theory is more accurate than the other developed theories for sandwich panels. In this study, the variation of the nondimensional natural frequency with respect to the various parameters is presented. POLYM. COMPOS., 31:2042–2048, 2010. © 2010 Society of Plastics Engineers