Failure Mode Of Sandwich Panels Research Articles

Fabrication and mechanical properties of thermoplastic corrugated sandwich panel with enhanced face‐core interface

AbstractThermoplastic sandwich structures are widely utilized in engineering fields due to their high specific strength and stiffness, recyclability, and impact toughness. The face‐core interface strength is crucial to maximize the performance benefits of sandwich structures. Two sizes of corrugated sandwich panels with hot‐melt bonding and resistance welding connection methods were fabricated. The mechanical properties of sandwich panels were compared using a combination of experimental, numerical, and analytical investigation. Edgewise compression (EC) and 3‐point bending (3 PB) tests were conducted to obtain load–displacement curves and investigate different failure modes of sandwich panels. The peak edge compression and bending loads of the resistance welded structures were 42% and 92% higher, respectively, and the face‐core interface was always well‐connected compared to those of the hot‐melt bonding. The results indicate that the resistance welding method can be utilized as a core bonding technique for thermoplastic composite sandwich structures and has great potential for aerospace application.Highlights A method that includes hot‐melt bonding and resistance welding are develop to produce thermoplastic composite corrugated sandwich panels (TPC‐CSPs). The TPC‐CSPs fabricated by resistance welding exhibit superior interface connection performance compared to hot‐melt bonding and this method enhance the structural load bearing capacity. The numerical and analytical method were presented to investigate the failure model, which was consistent with the experimental results.

Dynamic response and failure of CFRP Kagome lattice core sandwich panels subjected to low-velocity impact

Dynamic response and failure of carbon fiber reinforced plastic (CFRP) Kagome lattice core sandwich panels subjected to low-velocity impact were investigated experimentally and numerically. The geometrical shapes of the impactor noses are flat, hemispherical, and conical. The active failure modes of fiber fracture, matrix crack, delamination of face sheets, rib inclining/fracture of lattice core, and debonding were observed in experiment. The impactor nose shape has significant influence on the failure modes of sandwich panels. The energy absorption of sandwich panel increases with increasing impact velocity. The sandwich panel struck by the flat impactor has the highest energy absorption among three impactor noses. Finite element (FE) simulations implementing a user-defined material subroutine (VUMAT) of Hashin criterion and progressive degradation were performed and agree well with the experimental results. It is shown that both dynamic response and energy absorption of the sandwich panels are sensitive to the impactor size and impact position.

Low velocity impact penetration response of foam core sandwich panels with face sheets

Foam aluminum sandwich panels have potential applications in many fields because of their excellent performance. This study aims to explore the low velocity penetration dynamic response of foam sandwich panels. Based on the experimental results, a three-stage penetration model is established. Based on the principle of energy conservation, minimum potential energy and accumulating damage theory, the load and displacement time history, energy absorption and initial failure mode of the sandwich panel during penetration are predicted theoretically. The theoretical prediction results are compared with the experimental results, showing that the predicted failure load and deformation are within 10% of the experimental data. This paper provides an analytical method for studying the deformation failure mode and energy absorption mechanism of metal foam sandwich panels, which is helpful to improve the efficiency of metal foam sandwich panels in design.

A couple-stress model to predict the wrinkling stress of sandwich panels with foam cores

Wrinkling is a common failure mode of sandwich panels under in-plane compression. The classic methods often underestimate the wrinkling stress, especially for sandwich panels with low-relative-density foam cores. Hence, an accurate method for predicting wrinkling stress is desirable. This study proposes a new method to compute the wrinkling stress of sandwich panels. The foam core was taken as a couple-stress continuum with characteristic length, and the bending deformation of core materials was contained in the strain energy computation. The results showed that the predicted wrinkling stress agreed dramatically well with the experimental data. The computed wrinkling stress showed a significant size dependence on the cell size of the foam core. The bending deformation of the core material was significant for large characteristic length. Hence, our method expanded the classic work on predicting the wrinkling stress of sandwich panels, and we suggest that it should be used in the wrinkling analysis of sandwich panels with cellular solids.

On the structural parameters of honeycomb-core sandwich panels against low-velocity impact

This paper presents a combined experimental and numerical study on the low-velocity impact behavior of honeycomb-core sandwich panels with different structural parameters, including facesheet thickness, core height, honeycomb cell size, and cell wall thickness. Impact tests were conducted at four different energies using a drop-weight impact facility, and the deformation and damage characteristics of the tested sandwich panels were analyzed by microscopic X-ray computed tomography. The experimental results revealed two distinct failure modes of sandwich panels: namely mode A, with localized damage in both facesheets and core, which is dominated by indentation; and mode B, which is characterized by global bending deflection of the facesheets and overall core crushing. It was found that a sandwich panel with thin facesheets and a high-density honeycomb core (e.g. with a small cell size and/or a thick cell wall) tended to fail in mode A, but core height did not influence the failure mechanism notably. Furthermore, finite element modeling was carried out to gain further understanding of the effects of these structural parameters. The perforation resistance and energy absorption capacity were significantly enhanced with increasing facesheet thickness. Whereas reducing the cell size and/or thickening the cell wall resulted in lower perforation resistance. When the total thickness of facesheets remained a constant, the impact behavior of the sandwich structure could be optimized by controlling the thickness ratio of the front to back facesheets. Finally, cost efficiency analysis was performed to achieve a rational design of the sandwich structure considering both the impact performance and cost.

Quasi-static indentation characteristics of sandwich composites with hybrid facesheets: Experimental and numerical approach

The load response, energy absorption, different damage mechanisms and failure modes of sandwich panels subjected to complete perforation by quasi-static indentation and the insights gleaned are presented in this paper. The experimental campaign was carried out on samples made of different type of facesheets: Aluminium, glass fibre-reinforced plastic and metal-composite hybrid (combined aluminium and GFRP) with two different core heights. Reliable numerical models were developed with appropriate constitutive material and damage model for facesheets and honeycomb core to complement the experimental observations. Good agreement between experimental results and numerical predictions in terms of force-displacement response and perforation damage ensure the fidelity of the developed numerical model. Effects of facesheet type, core height, energy absorbed by the constituent layers, damage evolution history are briefly discussed. It was observed that the energy absorption of sandwich panels and peak indentation force resisted by the top and bottom facesheet are strongly dependent on its metal-volume fraction, whilst unaffected with the height of the core. Recommendations for developing computationally efficient numerical models were provided.

Mechanical properties of Nomex honeycomb sandwich panels under dynamic impact

Through experiments and numerical simulation, the dynamic mechanical behaviors and mechanical properties of Nomex honeycomb sandwich panels under impact loads were investigated. On this basis, the effects of the density of honeycomb cores, face-sheet thickness, punch diameter, and impact energy on impact loads and failure modes were explored. The predicted contact time, impact load, and failure mode were consistent with the test results. Results showed that face-sheet thickness exhibited an extremely significant influence on the impact resistance of Nomex honeycomb sandwich panels; the density of honeycomb cores exerted a certain effect on the structural stiffness; the punch diameter and impact energy also influenced the mechanical properties and failure modes of sandwich panels.

Predicting fracture mechanisms in synthetic foam sandwiches with multi-layered cores using extended cohesive damage model

This paper introduces an investigation on fracture mechanisms of synthetic foam sandwiches with graded multi-layered cores. The extended cohesive damage model (ECDM) is used in investigating detailed fracture mechanisms of this kind of synthetic foam sandwich panels under quasi-static 3-point bending. The ECDM prediction shows very good agreements with experimental work on investigating the sandwiches with homogeneous core and the core with four graded layers. This investigation has found that the failure modes of sandwich panels with multi-layered cores are sliding shear failure dominated fracture in the core along the path above the core-bottom sheet interface instead of pure debonding at interfaces. It has been also found an excellent mechanical performance when the core has multiple graded layers in the investigated sandwiches compared to the case of homogenous core. It is the first time that the correlation between loading capacity and number of graded layers in the core of the investigated synthetic foam sandwiches is explored. The ECDM predicted loading capacity of the investigated sandwich panel with an 8-layered core is increased by 70% compared to a homogenous core. This investigation also shows that the ECDM is a robust tool for predicting fracture mechanisms of synthetic foam sandwiches.

The low-velocity impact and compression after impact (CAI) behavior of foam core sandwich panels with shape memory alloy hybrid face-sheets

Abstract Due to the properties of shape memory effect and super-elasticity, shape memory alloy (SMA) is added into glass fiber reinforced polymer (GFRP) face-sheets of foam core sandwich panels to improve the impact resistence performance by many researchers. This paper tries to discuss the failure mechanism of sandwich panels with GF/ epoxy face-sheets embedded with SMA wires and conventional 304 SS wire nets under low-velocity impact and compression after impact (CAI) tests. The histories of contact force, absorbed energy and deflection during the impact process are obtained by experiment. Besides, the failure modes of sandwich panels with different ply modes are compared by visual inspection and scanning electron microscopy (SEM). CAI tests are conducted with the help of digital image correlation (DIC) technology. Based on the results, the sandwich panels embedded with SMA wires can absorb more impact energy, and show relatively excellent CAI performance. This is because the SMA wires can absorb and transmit the energy to the outer region of GFRP face-sheet due to the super-elasticity-behavior. The failure process and mechanism of the CAI test is also discussed.

Experimental Study on Bending Performance of Composite Sandwich Panel with New Mixed Core

This paper presents an experimental investigation of bending performance of composite sandwich panels with new mixed core, sandwich panels were tested by four-point bending test. Parametric study was conducted to investigate the influence of different core materials on the failure mode, ultimate bearing capacity, stiffness and ductility of composite sandwich panels. The results of the experimental investigation showed that the mixed core can change the failure mode of sandwich panels. The failure mode of wooden panels is characterized by tensile failure of bottom wood, and the failure mode of composite sandwich panels with wood core is that the surface layer and core are stripped and the webs are damaged by shear, while the failure mode of composite sandwich panels with wood and polyurethane foam mixed core is the shear failure of the web. Composite sandwich panels with GFRP-wood-polyurethane foam core have better bending performance and can effectively reduce the weight of panels.

Axial Loading Tests and Simplified Modeling of Sandwich Panels with GFRP Skins and Soft Core at Various Slenderness Ratios

AbstractExperimental and analytical studies were conducted to investigate the axial strength and failure modes of sandwich panels with glass fiber reinforced polymer (GFRP) skins and soft polyurethane core. A total of 45 specimens of 78×150 mm cross-section and of lengths Le varying from 500 to 2,400 mm [i.e., slenderness ratio (KLe∶r) of 15–70, where r is the radius of gyration] were tested concentrically using pin-ends (K=1). The effects of skin thickness and an internal GFRP rib on axial behavior were studied. The study first assessed the level of out-of-straightness and concluded that all specimens generally fall within an acceptable limit of span/1,000. A model based on sandwich panel theory, accounting for excessive shear deformations of the soft core, was used to predict axial strength at a wide range of KLe∶r and then used in a parametric study. It was shown that short panels with KLe∶r of 15–17 experienced local failure, outwards skin wrinkling in non-ribbed panels, or skin crushing in ribbed pa...

Effects of thermal exposure on mechanical behavior of carbon fiber composite pyramidal truss core sandwich panel

An experimental study was performed to investigate the effect of high temperature exposure on mechanical properties of carbon fiber composite sandwich panel with pyramidal truss core. For this purpose, sandwich panels were exposed to different temperatures for different times. Then sandwich panels were tested under out-of-plane compression till failure after thermal exposure. Our results indicated that both the thermal exposure temperature and time were the important factors affecting the failure of sandwich panels. Severe reductions in residual compressive modulus and strength were observed when sandwich panels were exposed to 300°C for 6h. The effect of high temperature exposure on failure mode of sandwich panel was revealed as well. Delamination and low fiber to matrix adhesion caused by the degradation of the matrix properties were found for the specimens exposed to 300°C. The modulus and strength of sandwich panels at different thermal exposure temperatures and times were predicted with proposed method and compared with measured results. Experimental results showed that the predicted values were close to experimental values.

High Velocity Impact Deformation of a Laser Welded Sandwich Panels

Underwater impact and explosion are the main methods that destroy the warships, it cause attention of countries with marine power. The all metal laser welded sandwich panels has the higher stiffness and better mechanical behavior, and be used to protect for warships against impact. This paper analyzed the displacement of sandwich panel on light impact object with different impact velocity , which show that: (1) The top plate penetrate at the impact velocity of 185m/s, then the bottom plate is penetrate when the impact velocity approaches to 275m/s. (2) The displacement of top plate is confined to the scope of 60mm along x-axis and 40mm along Y-axis from the impacting point at a high impact velocity, the failure mode of sandwich panel is serious partial destruction and obvious shear failure.

Temperature effects on the strength and crushing behavior of carbon fiber composite truss sandwich cores

The effects of temperature on the mechanical behaviors of composite rods and carbon fiber composite truss sandwich cores were investigated in this paper. Strength and stiffness of composite rods in fiber-aligned direction were measured in the range of −60°C to 260°C and characterized as functions of temperature. The research on out-of-plane compressive properties of sandwich panels with truss cores for temperature variation indicated that strength and failure modes of sandwich panels were significantly dependent on temperature. The stiffness and strength of composite rods and sandwich panels decreased progressively as temperature increased. The decreasing of stiffness and strength at high temperature was mainly attributed to softening of the polymer matrix. The increasing of stiffness and strength at cryogenic temperature was due to reduced mobility of the polymer chains within the resin matrix and the more closely compacted molecules of resin matrix. In order to provide insight into the effect of temperature on failure mechanism, the interface between fiber and matrix was examined using scanning electron microscope, and good interfacial bonding condition was observed at cryogenic temperature. The stiffness and strength of sandwich panels at different temperatures were predicted with proposed method and compared with measured results. Good agreement was observed between the measured values and predictions.

Local Buckling Design Rules for Profiled Sandwich Panels Based on the Studies of Foam-Filled Steel Beams

Modern composite sandwich constructions have been used very successfully in many aerospace and structural applications. Various aspects of structural behaviour of sandwich panels have been researched for many decades as they are a potential load carrying component in buildings. Sandwich panels exhibit various types of buckling failure modes depending on the types of steel faces used. Local buckling is one of the fundamental failure modes of sandwich panels with profiled faces. To investigate the local buckling behaviour, Davies & Hakmi (1992) conducted a series of bending tests of foam-filled thin-walled steel beams and developed a design method that is now adopted in the European recommendations for the design of sandwich panels (CIB, 2000). However, recent studies by Pokharel & Mahendran (2003; 2004a; 2004b) have shown that this design method is inadequate for sandwich panels with very slender plate elements, and therefore developed a new design rule that is applicable for a wide range of width-to-thickness (b/t) ratios of foam supported plate elements. This research was undertaken to investigate the applicability of these design rules based on the results from Davies & Hakmi’s (1992) bending tests of foam-filled steel beams and a numerical study simulating the bending tests. Both the experimental and numerical results were then compared with the predictions from the current and newly developed design rules. This paper presents the details of Davies & Hakmi’s (1992) bending tests and corresponding numerical modelling, evaluation and comparison of results.

Sandwich Beam with a Periodical and Graded Core Manufactured Using Rapid Prototyping

This article presents a technique for the production of graded sandwich cores, and a study of the effect of lengthwise grading of core properties for the facilitation of transverse loading. A significant failure mode of sandwich panels is caused by indentation of the foam core in regions at which local forces are introduced into the sandwich panel. The aim of this work is to synthesize a microstructure that can diminish this failure mode. By applying a rapid prototyping technique a periodic, open beam structure is synthesized. Additionally, the structure has been graded in the longitudinal direction by alternating over the beam diameter. The structure obtained is joined to aluminium face sheets to form a sandwich beam. The panel has been subjected to a three point bending test and the results have been compared to a finite element model, and further indentation tests show an increased transverse stiffness in the strengthened part of the beam.