Experimental and numerical investigation of the effect of asymmetry on the residual strength of a composite sandwich panel

Composite sandwich materials provide high bending performance-to-weight ratios. However, these materials are vulnerable to impact damages which can drastically reduce their load-bearing capability. Presently there is a lack of standardised test methods for impact assessment. This study compares three different test methods for impact assessment; single skin compression after impact (CAI-SS), sandwich compression after impact (CAI-SW) and four-point bending-after-impact (BAI). The CAI-SS test method shows high compressive strength and strain at failure and the tesr is relatively easy to evaluate. For finite size plates with significant impact damage, the CAI-SS test method is recommended for post impact strength assessment. For large sandwich panels with relatively small impact damages the CAI-SW test method could be more relevant since it includes effects of panel asymmetry generated from the impact damage. The BAI test method may be recommended as an alternative to CAI but quite long specimens are required in order to assure compressive failure in the tested face-sheet, making the test both demanding and expensive. On the other hand, lower load levels are required to break the specimens and there is less need for precise machining during specimen manufacturing. A finite element model including progressive damage evolution was used to estimate the post impact strength. The simulations showed generally good agreement with the experiments.

Section: Experimental Methodologymentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Evaluation of test methods and face-sheet thickness effects in damage tolerance assessment of composite sandwich plates

Rajput

Burman

Hallström

2021

“…The results of the examined experiments showed that use of elastomeric foam core for the sandwich beams makes a great residual strength in these components after failure of the top skin. The residual strength of the sandwich structures with crushable foam cores after failure is not usually considerable [24,25]. Another advantage of the elastomeric foam cores is recoverability of the deformations, seen in the core instead of permanent deformations which take place in the crushable foams.…”

Section: Sandwich Beams Under 3pb Conditionsmentioning

confidence: 99%

Experimental investigations on the sandwich composite beams and panels with elastomeric foam core

Nazari

Hosseini‐Toudeshky

Kabir

2017

In this paper, the load-carrying capacity and failure mechanisms of sandwich beams and panels with elastomeric foam core and composite laminate face sheets are investigated. For this purpose, the flexural behavior of laminated composite beams and panels (applied as face sheets) is firstly investigated under three-point bending and central concentrated loads, respectively. Then, the same examination is conducted for the sandwich beams and panels, in which the proposed elastomeric foam is utilized as the core material. It is shown that the failure mechanisms which are associated to the core in the sandwich structures with crushable foams are not considered in the examined sandwich structures. The collapse of the sandwich specimens, examined here, is observed due to the failure of the skins in some steps. By multi-step collapse of these specimens via separately failure of the top and bottom skins, a considerable amount of energy is absorbed between these steps. Due to non-brittle behavior of the core material under loading, a large compression resistance is observed after failure of the top skin which led to the recovery of the load-carrying capacity in the sandwich beams. A similar behavior for the sandwich panels led to the increase of the ultimate strength after appearance of the failure lines on the top skin. The general outcomes of this investigation promise a good influence for the application of elastomeric foam as core material for sandwich structures.

“…In addition to impact, there have been studies that deal with the compressionafter-impact (CAI) behaviour of sandwich panels. The CAI of sandwich panels with damage confined to the face laminates has been extensively investigated in many research works [20][21][22][23][24]. In Shipsha and Zenkert [25], the CAI strength of composite sandwich panels with core crushing damage was studied.…”

Section: Introductionmentioning

confidence: 99%

Residual bending behaviour of sandwich composites after impact

Baran

Weijermars

2018

This work investigates the residual mechanical behaviour of composite sandwich panels in bending after impact loading conditions. The sandwich panels were made of an epoxy/glass face sheet with three different core materials: styrene acrylonitrile foam, polyethylene terephthalate foam and Balsa wood. A three-point bending test was performed in order to determine the reference stiffness. A low-velocity impact test and thereafter the three-point bending test were performed with the same specimens. The failure modes during bending tests were captured using a high-speed camera. It was found that multiple shear cracks with progressive failure were present in the core of styrene acrylonitrile and polyethylene terephthalate panels in bending after impact tests, whereas single shear crack with sudden failure was the case for Balsa panels. The initial bending stiffness decreased approximately 30.5, 35.2 and 55.6% for Balsa, styrene acrylonitrile and polyethylene terephthalate panels, respectively, in bending after impact tests due to the influence of the pre-damage from the low-velocity impact tests. The reduction in collapse force was also quantified for Balsa, styrene acrylonitrile and polyethylene terephthalate panels as 22.8, 4.9 and 22.1%, respectively.