1. SANDWICH COMPOSITE BEAMS for STRUCTURAL APPLICATIONS
de Aguiar, José M. ,
Faculdade de Tecnologia de São Paulo, FATEC-SP
Centro Estadual de Educação Tecnológica Paula Souza. CEETEPS
Praça Coronel Fernando Prestes, 30 - Bom Retiro - São Paulo-SP - CEP  
de Aguiar, João B. ,
Universidade Federal do ABC
Centro de Engenharia, Modelagem e Ciências Sociais Aplicadas.  Av. dos Estados, 5501 Bangu Santo Andre, SP - Brasil

2. Structural Sandwich Composite Beam
Special laminated composite type produced by bonding thin stiff skins (two) to lightweight thick core;
Sandwich beam made of:
Core material : modified phenolic (endure harsh weather, resists chemical and corrosion, extreme temperatures, low humidity absorption)
Skin material : bi-axial glass fiber
Advantage:
elevated bending stiffness/weight ratio;
high impact strenght and corrosion resistance;
high strength core can hold mechanical connectors ( compared to honeycomb and trussed core options)
high strength core holds compressive load compared to traditional soft cores.
Structural beam sections can be formed by gluing sandwiches beam modules due to limited thicknesses availability:
Horizontal skins
Vertical skins H H

3. Four point bending test
Property
Skin
Core
Young´s Module (MPa)
14280
1150
Maximum tensile stress (MPa)
242 14
Maximum compressive stress (MPa)
211 21
Thickness (mm)
1.92
16.16

5. Rectangular beam – Horizontal position
Rectangular beam – Horizontal position. Vertical displacements (1LSW_F) Load P=4550 N H
Dimensions B H L
Horizontal
50 mm
20 mm
400 mm
Core material W mm

6. Core material: Tensile stress less than 5 % of max core tensile stress Tension cracks appear at bottom of core material
Mechanical Property
Compressive
Tensile
Core max stress
21 MPa
14 MPa

7. Bottom skin layer: Tensile stress less then 15% of max tensile skin stress
Mechanical Property
Skin
Core
Max tensile stress
242 MPa
14 MPa

8. Failure Mode: compressive skin failure Compressive skin stress less than 1% of max compressive stress
“Specimen 1LSW-F failed due to compressive failure of the fibre composite skin followed by delamination between the core and the skin.” A.C.Manalo
Mechanical Property
Skin
Core
Max compressive stress
211 MPa
21 MPa

9. Rectangular beam – Vertical position.
Vertical displacements (1LSW_E) Load P=5000 N
“The load capacity of specimen 1LSW-E increased linearly with deflection but showed reduction in stiffness at a load of around 5000 N due to the tensile cracking of the core.” A.C.Manalo H
Skin
Core
Young´s Module
14280 (MPa)
1150 MPa
Vertical Position
B=20 (mm)
H=50 (mm)
Thickness
1.92 (mm)
16.16 (mm)

10. Core material: Tensile stress exceeds core max tensile stress
“Tensile core cracks were also observed in specimen 1LSW-E. The presence of non-horizontal skin prevented the premature failure of the core” A.C.Manalo
Dimensions B H L
Horizontal
20 mm
50 mm
400 mm
Mechanical Property
Skin
Core
Max tensile stress
242 MPa
14 MPa H

11. Failure Mode: Progressive compressive failure of non-horizontal skins
“The specimen 1LSW-E failed due to progressive compressive failure of the skin followed by tensile failure of the skins. “ A.C. Manalo
Mechanical Property
Compressive
Stress
Tensile
Skin
242 MPa
211 MPa

12. Conclusions
FEM results permits to infer the failure scenario shown on flexural testing of structural composite beams;
Fem models for glueded laminated sandwiches : side by side and piled up cross-sections can be developed to speculate about failure modes;
The beam strength depends on the number and combination of laminated skins;
The effect of load-distribution of the gluing certainly needs to be taken into account into the failure scenario.
Lack of information on non-linear effects as well as number and fiber orientation limits considerably the fem modeling simulations.