Behavior Of Sandwich Composites Research Articles

Experimental and numerical studies on quasi‐static behavior of sandwich composites with nano clay modified Kevlar facesheets and aluminum honeycomb core

AbstractThis study investigates the influence of nano clay reinforcement on the mechanical behavior of Kevlar/epoxy composite laminates and sandwich structures subjected to quasi‐static punch shear loading. Three types of composite face sheets were fabricated using hand lay‐up technique: Kevlar/epoxy neat, 0.5, and 1 wt. % of nano clay. The mechanical properties of these composites were characterized through compression, shear, and tensile tests. Sandwich structures were then constructed using the fabricated face sheets and an aluminum honeycomb core. Quasi‐static punch shear tests were performed on the composite laminates and sandwich specimens using hemispherical impactors. Numerical simulations of the punch shear tests were conducted in LS‐Dyna, employing appropriate material models and contact definitions for the constituent materials. Furthermore, to further investigate the failure mechanisms, scanning electron microscopy (SEM) analysis was conducted on the fractured Kevlar/epoxy composite plate specimens. The comparison between the experimental outcomes and numerical data demonstrated a strong correspondence, indicating consistency between the two methodologies. In conclusion, the incorporation of 0.5 wt. % nano clay into the Kevlar/epoxy composite resulted in a 5.09% increase in shear strength and an 11.29% increase in maximum reaction force. The study provides insights into the effect of nano clay reinforcement on the punch shear resistance and energy absorption capabilities of Kevlar/epoxy composites and sandwich structures.Highlights Proper alignment of the nano clay within the epoxy was achieved. The most efficient rate of nano clay was observed to be 0.5% by weight. The mechanical properties of nano clay‐containing composites were improved. Quasi‐static punch shear tests were performed numerically and experimentally. Numerical results were in close agreement with experimental results.

Characterization of sandwich beams with shear damages by linear and nonlinear vibration methods

The aim of the present work is to study the vibration behavior of sandwich composites with shear damages on the foams. The effect of the densities of damage on the linear and nonlinear vibration parameters is studied. The sandwich materials used in this study is constructed with glass fiber laminates as skins and with PVC closed-cell foams with density 60 and 100 kg m−3 as core. After a serie of vibration tests, the change of natural frequencies and modal damping due to the damage and the foam densities. For an intact specimen, the resonance frequency was constant when we increase the excitation amplitude. For damaged specimens, the resonance frequencies decrease and the loss factors increase proportionally with the increasing excitation amplitude. The nonlinear parameters corresponding to the elastic modulus and damping were determined for each frequency modes and each damage and foam densities. The results showed that nonlinear dissipative parameters were more sensitive to damage than linear elastic and dissipative parameters.

Fatigue of Sandwich Composites in Air and Seawater

In this study, the fatigue behaviour of sandwich composites was investigated in both, air and seawater. S–N curves were obtained for different stress levels. 3-point bending (3PB) tests were also performed to investigate strength degradation during the fatigue test. Finite element analyses were carried out to determine the stress distribution in the test coupons used in bending tests. These were used to predict the failure of the composite and to interpret the experimental results. There is good agreement between finite element analysis and experimental results at lower loads. Small deviations were observed at higher loads due to the influence of defects. The typical failure modes observed under quasi-static 3PBT were debonding, fibre pull-out and matrix cracking.

Interfacial Creep Fracture Behavior of Foam Core Sandwich Composites with Different Resin

Interfacial creep fracture behavior of sandwich composites consisting of E-glass/ unsaturated polyester (UPE) resin and E-glass/vinyl ester (VE) resin facings over PMI foam core has been experimentally investigated. Digital image correlation (DIC) method was employed in the double cantilever beam (DCB) test to measure the creep displacement field surrounding the crack tip. Crack opening displacements (COD) at various creep time were extracted from the creep displacement field and mode I stress intensity factors were determined using the small region COD-based linear extrapolation method. Significant increments of COD and nominal stress intensity factor are found in specimen with UPE resin and specimen with VE resin after 24 hours creep test. It is also found that specimen with UPE resin has a better interfacial creep fracture resistance than that of specimen with VE resin.

Damage Behavior of Foam Core Sandwich Composites Subjected to Quasi-Static Indentation Testing

Damage behavior of foam core sandwich composites subjected to quasi-static indentation testing was investigated detailedly. Force-displacement curves and the cross-sections of damaged sandwich panels were analyzed. Effects of core thickness, face-sheet thickness and toughness of face-sheet materials were discussed by comparison with different specimens subjected to quasi-static indentation testing. Results showed that damage behavior of sandwich composites had identical feature. Collapse of foam core initially appeared, and then foam core generated crack. Delamination and fiber breakage of upper face-sheet occurred. Finally, the foam core and the face-sheet were disengaged. For the specimens with thick foam cores, the foam crack extended in longitudinal direction was caused. However, for the specimens with thin foam cores, the foam cracked in transverse direction. After face-sheets were toughened with PAEK, the damage resistance and the maximum force of the sandwich panels increased. Also, the shear angle of foam crack changed to be lager. Compared with the penetrated damage behavior of sandwich panels with thin face-sheets, the upper face-sheets of the former the specimens with thick face-sheets bulged partially and could not be penetrated.

A review of noise control methods for composite structures.

Composite materials and structures offer great promise to all air vehicles and are being increasingly considered for lightweight advanced applications. However, composite structures are efficient radiators of noise mainly due to excitation and propagation of supersonic bending and/or shear waves in the structures. Composite skin-stringer structures mostly support supersonic flexural or bending waves propagating in the laminated structure whereas noise radiation by sandwich structures is dominated by supersonic shear waves in the core. The vibro-acoustic behavior of sandwich composites has been studied by several investigators. Wave number diagrams have been useful in identifying supersonic flexural and shear waves in composite structures. It has been shown that the radiating wave number components increase with increasing plate stiffness, causing increased sound radiation. Although design criteria for sandwich composites in terms of sub-sonic core wave speeds have been evolved, skin-stringer composite structures must use added noise control treatments. Noise control of composite structures, thus, still presents a significant technical challenge as the main advantages afforded by these structures, such as low weight and high strength, must not be compromised by added treatments. This paper presents a review of recent advances in the noise control techniques for composite structures.

Elastic-plastic deformation of sandwich rod on elastic basis

Sandwich composite material possesses advantages of both light weight and high strength. Although the mechanical behaviors of sandwich composite material with the influence of single external environment have been intensively studied, little work has been done in the study of mechanical property, in view of the nonlinear behavior of sandwich composites in the complicated external environments. In this paper, the problem about the bending of the three-layer elastic-plastic rod located on the elastic base, with a compressibly physical nonlinear core, has been studied. The mechanical response of the designed three-layer elements consisting of two bearing layers and a core has been examined. The complicated problem about curving of the three-layer rod located on the elastic base has been solved. The convergence of the proposed method of elastic solutions is examined to convince that the solution is acceptable. The calculated results indicate that the plasticity and physical nonlinearity of materials have a great influence on the deformation of the sandwich rod on the elastic basis.

Parameters of Construction for Applications of Metal Foams

ABSTRACTThis article will present characteristics that have great importance for the industrial use of metal foam structures. In detail, these areDesign criteria for detachable joint connectionsInvestigation of the thermal behavior of sandwich composites