Specific Properties of Novel Two- Dimensional Square Honeycomb Composite Structures M.R.M.Rejab, W.A.W.Hassan, J.P.Siregar and D.Bachtiar 1

Outline 2 1.Introduction 2.Motivation 3.Square Honeycomb Sandwich Structures 4.Experimental Work and Results 5.Specific Energy and Energy Absorption 6. Conclusions 7. Further Works

Introduction 3 Sandwich structures ~ fibre reinforced plastic skins + a cellular core = superior weight specific stiffness and strength properties In recent years, many researchers have proposed various core designs with an improved quasi-static and dynamic performance : polymeric and aluminium foams, metallic trusses, honeycomb cores (hexagonal, triangular) and prismatic cores (diamond lattice and corrugation).

Introduction 4 Previous studies have suggested that square honeycomb cores having a higher relative density are preferable for use in high severity loading situations, such as blast loading as a result of their superior crushing resistance and in-plane tensile strength (Wierzbicki et al, 1983). YearDesignNovel TechniquesResults Coté et. al stainless steel (SS) sheets -6x6 cells - Slotting and then brazing the assembly -compared the SS core with AL hexagonal honeycomb core, same relative density and cell aspect ratio. -SS core offered a higher compression strength and absorb more energy compared

Introduction 5 YearDesignNovel TechniquesResults Russel et. al CFRP -6 x 6 cells - Slotting, assembling and adhesively bonding composite laminate sheets with various fibre orientations; [0/90], [±45]. -CFRP core with a relative density of 0.2, with a weave [0/90] for specimen based on 6 x 6 cells gives a higher compressive strength and energy absorption

Introduction 6 YearDesignNovel TechniquesResults Deshpande et. al GFRP/PMI foam The cell walls of the square honeycomb comprise sandwich plates made from glass fiber/epoxy composite skins and a PMI foam core. The square honeycomb core shows promise as it has a substantially higher through- thickness compressive strength than an equivalent sandwich panel with a monolithic composite core.

Introduction 7 YearDesignNovel TechniquesResults Rejab et. al ?? ?

Motivation 8 The current work focuses on manufacturing novel square honeycomb cores and with recyclable materials The compressive responses when subjected to uniform lateral loading are then investigated. The specific strength and specific energy absorption are explained quantitatively and then compared with other competing cores design.

Square Honeycomb Sandwich Structures 9 Design of Square Honeycomb Core (a) 2 x 2 unit cells with slotting technique assembly(b) Unit cell and relative density Parameter for study: D=30mm L=20mm H=varies thicknesses

10 Design of Square Honeycomb Core (a) Core structure(b) Core with semi-rigid PVC foam (H130) Foam (20mm x 20mm x 30mm) Square Honeycomb Sandwich Structures

11 NoMaterialYoung’s Modulus, E(GPa) Ultimate Tensile Strength, UTS (MPa) 1Unidirectional Glass Fibre UD001/ Woven Carbon Fibre prepreg EP121- C Self Reinforced Polypropylene- Curv TM – C100A Semi-rigid PVC foam (H130) Material properties Adhesive properties 1. Source of data from Primco Limited datasheet ; 2.Source of data from Gurit AG datasheets 3.Source of data from ProPex Fabrics datasheet ; 4. Source of data from Diviniycell datasheets NoMaterial Lap Shear Strength, LSS (MPa)Remarks 1Araldite 420 A/B Structural Adhesive43Cured at 120 o C for 1 hour 2Xiro Colano PP Film (60μm)11155 o C for binding 1.Source of data from Hunstman Advanced Materials datasheet 2.Source of data from Collano Smart bonding datasheet Square Honeycomb Sandwich Structures

12 Material, geometry and densities of the square honeycomb cores LabelGF1GF1FGF2GF2FCF1CF1FCF2CF2FSRPP MaterialUnidirectional GFRPWoven CFRP Woven PP Fibre direction[0/90] s [0/90/0/90] s [0/90] Wall thickness, H (mm) Core relative density, 0.1 With foam 0.2 With foam 0.1 With foam 0.2 With foam 0.3 Core density, (kg/m 3 ) Square Honeycomb Sandwich Structures

13 1. Adhesive bonding (epoxy) for GFRP & CFRP specimens 2. Fusion technique (PP film ~thickness of 60μm) for SRPP specimen Fabrication of Sandwich Structures Square Honeycomb Sandwich Structures Skin PP film Core Adhesive lines

Experimental Work 14 Stress-strain curves of GFRP square honeycomb sandwich structures Compressive responses of GFRP specimens (different relative density)

Experimental Work 15 Stress-strain curves of GFRP square honeycomb sandwich structures Compressive responses of GFRP specimens (adding foam core)

Experimental Work 16 Stress-strain curves of CFRP square honeycomb sandwich structures Compressive responses of CFRP specimens (different relative density)

Experimental Work 17 Stress-strain curves of CFRP square honeycomb sandwich structures Compressive responses of CFRP specimens (adding foam core)

Experimental Work 18 Stress-strain curve of SRPP square honeycomb sandwich structure Compressive responses of SRPP specimen

Specific Energy and Energy Absorption 19 The compressive strength and energy absorption of all the square honeycomb cores were divided by weight of the core, to yield a strength-to-weight ratio or specific strength (σ sp ) and specific energy absorption (E sp ) at a strain ε = 0.7 are compared using this intrinsic property. The specific strength and specific energy absorption of the square honeycomb sandwich structures

Specific Energy and Energy Absorption 20 The specific strength and specific energy absorption of the competing core types design

Specific Energy and Energy Absorption 21 The specific strength and specific energy absorption of the competing PP core types design

Conclusions 22 The manufacturing route and compressive responses of the square honeycomb cores of three different materials subjected to uniform lateral compression were discussed in detail. The following conclusions are made: 1.The square honeycomb cores were made from slotting technique and they have outstanding properties in terms of the σ sp and E sp compared with other commercial core. The CFRP cores are the best type of material for this novel design and fabrication process. 2. The SRPP square honeycomb sandwich structure is a new novel sandwich structure where a thin PP film is used to bond the skins and core, and made them 100% recyclable sandwich structure. This potential core type design and material is a suitable candidate for aerospace applications in a near future.

Further Works 23 1.Modeling with FE 2.Experiments would be extended to transverse shear properties using Arcan testing technique and the behaviour of square honeycomb sandwich structure under various dynamic loadings.

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