scholarly journals Flexural Response of Degraded Polyurethane Foam Core Sandwich Beam with Initial Crack between Facesheet and Core

Materials ◽  
2020 ◽  
Vol 13 (23) ◽  
pp. 5399
Author(s):  
Gurpinder Singh Dhaliwal ◽  
Golam M. Newaz
Keyword(s):  
Loading Rate ◽  
Peak Load ◽  
Sandwich Beam ◽  
Initial Crack ◽  
Flexural Behavior ◽  
Sandwich Beams ◽  
Damage Initiation ◽  
The Core ◽  
Flexural Response ◽  
Core Thickness

Structural systems developed from novel materials that are more durable and less prone to maintenance during the service lifetime are in great demand. Due to many advantages such as being lightweight as well as having high strength, corrosion resistance, and durability, the sandwich composites structures, in particular, have attracted attention as favorable materials for speedy and durable structural constructions. In the present research, an experimental investigation is carried out to investigate the flexural response of sandwich beams with a pre-cracked core-upper facesheet interface located at one end of the beam. During the development of the sandwich beams, an initial pre-cracked debond was created between the core and facesheet by placing a Teflon sheet at the interface. Both three-point and four-point flexural tests were conducted to characterize the flexural behavior of the sandwich beams. The effects of the loading rate, core thickness, and placement of the initial interfacial crack under a compressive or tensile stress state on the response and failure mechanism of Carbon Fiber-Reinforced Polymer (CFRP)/Polyurethane (PU) foam sandwich beams were investigated. It was found that the crack tip of the initial debonding between the upper facesheet and the core served as a damage initiation trigger followed by the fracture failure of the core due to the growth of the initial crack into the core in an out-of-plane mode. Finally, this leads to facesheet damage and rupture under flexural loadings. An increase in the core thickness resulted in a higher peak load, but the failure of the sandwich beam was observed to occur at significantly lower displacement values. It was found that the behavior of sandwich beams with higher core thickness was loading rate-sensitive, resulting in stiffer response as the loading rate was increased from 0.05 to 1.5 mm/s. This change in stiffness (10–15%) could be related to the squeezing of all pore space, resulting in the collapse of cell walls and thereby making the cell behave as a solid material. As a result, the occurrence of the densification phase in thick core beams occurs at a faster rate, which in turn makes the thick cored sandwich beams exhibit loading rate-sensitive behavior.

scholarly journals The Effects of an Interlayer Debond on the Flexural Behavior of Three-Layer Beams

Coatings ◽  
2019 ◽  
Vol 9 (4) ◽  
pp. 258 ◽  
Author(s):  
Ilaria Monetto
Keyword(s):  
Sandwich Beam ◽  
Flexural Behavior ◽  
Analytical Models ◽  
Model Parameters ◽  
Flexural Stiffness ◽  
Three Point Bending ◽  
Composite Action ◽  
The Core ◽  
Flexural Response ◽  
Multilayered Systems

Debonds at the interfaces between layers of multilayered systems make the degree of the composite action reduce. As a consequence, the global stiffness of such composites decreases. In order to investigate this reduction, even simplified analytical models are preferable to numerical analyses. This paper analyzes the flexural response of a three-point bending three-layer beam having a debonded portion at the upper interface to investigate the effects of the interlayer debond on the flexural stiffness of the three-layer beam and to examine the feasibility of detecting the presence of possible manufacturing or in-service flaws. A more general model proposed and validated previously by the author was specialized to solve the equilibrium problem considered. A parametric analysis was then performed on varying the model parameters and evaluating the maximum deflection to compare with that for perfectly bonded layers as a measure of the reduction of the flexural stiffness due to the presence of the debond. The numerical results obtained show that the flexural behavior of the sandwich beam under consideration is affected strongly by the length of the debond but only moderately by its position along the interface unless the outer faces are quite stiffer than the core.

scholarly journals Characteristics of CFRP/PU foam and GFRP/PU sandwich beams having initial debond between facesheet and core

2021 ◽  
Vol 3 (3) ◽  
Author(s):  
Gurpinder Singh Dhaliwal
Keyword(s):  
Polyurethane Foam ◽  
Sandwich Beam ◽  
Fiber Reinforced Polymer ◽  
Flexural Behavior ◽  
Face Sheet ◽  
Sandwich Beams ◽  
Fiber Reinforced ◽  
The Core ◽  
Reinforced Polymer ◽  
Pu Foam

AbstractIn the present investigation, we present, the flexural characteristics of carbon fiber reinforced polymer/polyurethane foam and glass fiber reinforced polymer/polyurethane foam sandwich beams having partial debonding between facesheet and core that acts interfacial degradation and hinders the load transfer between facesheets and core. An initial pre-crack between core and face sheet is created by placing a Teflon sheet at the interface on one end of the beams during the manufacturing of sandwich beams. A comparative analysis is carried out to study the effect of using CFRP and Eglass prepregs as face sheet material on such sandwich beams. The flexural behavior of GFRP/PU sandwich beams having initial debond is characterized and analyzed under both three- and four-point loadings. Lastly, the effect of varying the support span length on the flexural response of CFRP/PU sandwich beam having initial debond is also investigated. It was found that the degraded sandwich beams having woven CFRP facesheets have slightly higher stiffness and peak load level as compared to the sandwich beam having cross ply GFRP facesheets. GFRP/PU foam sandwich beam showed higher ductile behavior prior to progressive failure of the sandwich beam. It was observed that the crack tip of the implanted interfacial debond acts as a medium to trigger the interfacial damage followed by the shear failure of the core due to the progression of the initial crack into the core.

Finite Elements for Curved Sandwich Beams

1977 ◽  
Vol 28 (2) ◽  
pp. 123-141 ◽  
Author(s):  
P J Holt ◽  
J P H Webber
Keyword(s):  
Finite Elements ◽  
Stiffness Matrix ◽  
Test Cases ◽  
Sandwich Beams ◽  
Honeycomb Core ◽  
The Core ◽  
The Face ◽  
Core Thickness ◽  
Displacement Approach ◽  
Circular Sandwich Ring

SummaryThe formulation of curved finite elements to represent a two-dimensional circular sandwich ring with honeycomb core and laminated faces is investigated. Assumed stress hybrid and equilibrium methods are found to be easier to employ in this case than the displacement approach. Using these methods, an element stiffness matrix is developed. The approximations of membrane faces and an infinite core normal stiffness are then used to develop simpler elements. Test cases show that these assumptions may become invalid, but that they are adequate for most practical cases where the core thickness to radius ratio and the face thickness to core thickness ratio are both low.

The effect of interface debonding on flexural behaviour of composite sandwich beams

2018 ◽  
Vol 22 (4) ◽  
pp. 1132-1156 ◽  
Author(s):  
Mohsen Mansourinik ◽  
Fathollah Taheri-Behrooz
Keyword(s):  
Cohesive Zone Model ◽  
Sandwich Beam ◽  
Interface Debonding ◽  
Zone Model ◽  
Nonlinear Behaviour ◽  
Loading Capacity ◽  
Sandwich Beams ◽  
Failure Initiation ◽  
The Core ◽  
Composite Skins

In the current article, the behaviour of sandwich beams with and without initial core–skin debonding is studied under flexural loads through numerical and experimental procedures. Sandwich beams with three different lengths of 100, 180 and 280 mm and two types of composite skin layups of [0/90]2 and [45/–45]2 are fabricated. An initial artificial debonding is created between core and face sheets during manufacturing the flawed sandwich beams. Numerical simulations and experiments of the short- and medium-sized intact beams revealed that the dominant failure mode is foam yielding and crushing. Thus, the composite skins layup sequence has almost no effect on the failure initiation and growth of those beams. However, in the long-sized sandwich beams, the layup sequence changed the load–displacement response of the beams. Moreover, ignoring the nonlinear behaviour of the composite skins caused a remarkable deviation from the experiment. It is shown that sandwich beams with initial debonding placed in tension side had a negligible effect on the loading capacity of the beams, while those on the compression side had remarkable effects. For instance, the ultimate load of the long-sized beam decreased by 56% compared to the intact sandwich beam. Similarly, in the medium-sized beam, the core–skin debonding in the compressive side caused near 20% reduction in the loading capacity compared to the corresponding intact beam. The cohesive zone model and the extended finite element method were utilized successfully to capture crack initiation and propagation between the core–skin interfaces as well as inside the foam core. Acceptable agreement was observed between the experiment and numerical results.

Three-Point Bending Shear Stress of Wooden Sandwich Composite

2016 ◽  
Vol 852 ◽  
pp. 1337-1341
Author(s):  
Xin Feng Wu ◽  
Jian Ying Xu ◽  
Jing Xin Hao ◽  
Rui Liao ◽  
Zhu Zhong
Keyword(s):  
Shear Stress ◽  
Shear Force ◽  
Sandwich Beam ◽  
Single Layer ◽  
Skin Layer ◽  
Sandwich Composite ◽  
Three Point Bending ◽  
The Core ◽  
Sandwich Construction ◽  
Core Thickness

The effect of construction parameters and material type on bending shear stress and shear force was analyzed systematically. It is shown that maximum bending shear stress of sandwich construction is smaller than homogeneous single layer beam with same cross section if the skin has higher modulus than the core. Besides the effect of core or skin layer to shear force is almost identical for sandwich composite composed by different materials with same construction parameter. In addition, the shear force can be taken almost by the core of sandwich beam only if the ratio of core thickness to the whole is more than. Otherwise the resistance to shear force of skin layer should be considered to calculate the shear deformation. The results can provide basic theory for design optimization of sandwich construction.

The Efficiency of Auxetic Cores in Sandwich Beams Subjected to Low-Velocity Impact

2020 ◽  
Vol 12 (06) ◽  
pp. 2050061
Author(s):  
Mohammad Hedayatian ◽  
A. R. Daneshmehr ◽  
G. H. Liaghat
Keyword(s):  
Impact Energy ◽  
Test Procedure ◽  
Peak Load ◽  
Sandwich Beam ◽  
Low Velocity Impact ◽  
Sandwich Beams ◽  
Low Velocity ◽  
Velocity Impact ◽  
Unit Cells ◽  
Impact Area

This paper experimentally investigates the behavior of sandwich beam with auxetic core subjected to low-velocity impact loading. Two types of sandwich beams with different topologies of auxetic cellular cores were produced. Furthermore, a test procedure involving a cylindrical impactor was developed, and a parametric study was designed and performed. The results revealed that, at the same level of impact energy, the peak load decreased by increasing the re-entrant angle would make the auxetic sample with the highest re-entrant angle an ideal candidate for protective applications. However, in other applications where the structure needs to be protected from damage at a higher level of impact energy, the auxetic sample with the lowest re-entrant angle exhibited the best performance due to the highest amount of failure energy. Finally, the results showed that once the core structure changed from the conventional to auxetic, the energy level leading to damage to the structure increased so that it was escalated by a factor of 2 in the auxetic sample compared to the conventional sample. This is due to the negative Poisson’s ratio effect of structure that makes unit cells be drawn into the projectile impact area and, in turn, the structure is strengthened.

scholarly journals Simplified analytical model for tapered sandwich beams using variable stiffness materials

2016 ◽  
Vol 19 (1) ◽  
pp. 3-25 ◽  
Author(s):  
Qing Ai ◽  
Paul M Weaver
Keyword(s):  
Sandwich Beam ◽  
Shear Deformation Theory ◽  
Variable Stiffness ◽  
Axial Stiffness ◽  
Beam Model ◽  
Sandwich Beams ◽  
Element Analysis ◽  
The Core ◽  
The Face ◽  
Potential Energy Method

A simplified layer-wise sandwich beam model to capture the effects of a combination of geometric taper and variable stiffness of the core on the static response of a sandwich beam is developed. In the present model, the face sheets are assumed to behave as Euler beams and the core is modelled with a first-order shear deformation theory. With geometrical compatibility enforced at both upper and lower skin/core interfaces, the beam’s field functions are reduced to only three, namely the extensional, transverse and rotational displacements at the mid-plane of the core. The minimum total potential energy method is used in combination with the Ritz technique to obtain an approximate solution. Geometrically nonlinear effects are considered in the present formulation by introducing von Kármán strains into the face sheets and core. Two types of sandwich beams, uniform and tapered, with different boundary conditions are studied. Results show that the proposed model provides accurate prediction of displacements and stresses, compared to three-dimensional finite element analysis. It is found that due to the axial stiffness variation in the core, displacements of beams and stresses of face sheets and core are significantly affected. The potential design space is shown to be expanded by utilizing variable stiffness materials in sandwich constructions.

Static Response of Stiff-Cored Unsymmetric Sandwich Beams

1976 ◽  
Vol 98 (2) ◽  
pp. 391-396 ◽  
Author(s):  
D. K. Rao
Keyword(s):  
Variational Method ◽  
Flexural Rigidity ◽  
Sandwich Beam ◽  
Sandwich Beams ◽  
Static Response ◽  
Simply Supported ◽  
The Core ◽  
Distributed Load ◽  
Very High ◽  
Maximum Stresses

Improved equations governing the deflection of an unsymmetric sandwich beam (which include the effect of extensional and bending rigidities of its stiff core) are derived using a variational method. The effect of face-thickness ratio on the contribution of the core to the overall flexural rigidity is studied. Numerical results for simply supported and fixed-fixed beams subjected to a uniformly distributed load are obtained by using Laplace transforms. These results show that ignoring the bending and extensional effects of a stiff core can cause errors in maximum deflections as high as 20 percent. The corresponding errors in stresses are very high, and they vary from 10 to 150 percent. Hence, it is suggested that the extensional and bending effects of the core should be taken into account when one is interested in calculating the maximum stresses in stiff-cored beams.

scholarly journals Vibration Analysis of Carbon Fiber Reinforced Laminated Composite Skin with Glass Honeycomb Sandwich Beam Using HSDT

2017 ◽  
Vol 61 (3) ◽  
pp. 213 ◽  
Author(s):  
Mageshwaran Subramani ◽  
Ananda Babu Arumugam ◽  
Manoharan Ramamoorthy
Keyword(s):  
Finite Element ◽  
Aspect Ratio ◽  
Vibration Analysis ◽  
Natural Frequencies ◽  
Sandwich Beam ◽  
Laminated Composite ◽  
Element Model ◽  
Composite Sandwich ◽  
The Core ◽  
Core Thickness

In this paper, the vibration analysis of uniform laminated composite sandwich beam with a viscoelastic core was studied. The governing equation of motion of the laminated composite sandwich beam has been derived based on higher order shear deformation theory (HSDT) in finite element model (FEM). The developed finite element model has been validated in terms of natural frequencies with the experimental values and the available literature. Various parametric studies have been performed to examine the impact of the core thickness, ply orientation and aspect ratio of the uniform laminated composite sandwich beam in response to free vibration for various boundary conditions. From the results it was concluded that that natural frequencies could be increased with increasing the core thickness and decreased with increasing the aspect ratio.

Characterization of the Flexural Behavior of SMP Sandwich Beam

2010 ◽  
Vol 123-125 ◽  
pp. 939-942 ◽  
Author(s):  
Zheng Fa Li ◽  
Zheng Dao Wang
Keyword(s):  
Shape Memory ◽  
Sandwich Structures ◽  
Sandwich Beam ◽  
Shape Memory Polymers ◽  
Flexural Behavior ◽  
Sandwich Beams ◽  
Lower Recovery

Shape memory polymers (SMPs) can have a large frozen strain but providing much lower recovery stresses. To overcome such disadvantage, sandwich structures consisted of a SMP core and two thin metallic skins was considered. Due to much compliance of the SMP core, SMP sandwich beam is buckled at a lower packaging strain. Buckling is the fundamental character of SMP sandwich beam under bending. The critical buckling parameters about two types of SMP sandwich beams were theoretically derived.

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