Energy absorption in sandwich laminate structures Robert White IM 2005

INTRODUCTION Sandwich laminate boat hulls Maximum survivable impact speed at sea? Due to the nature of composite structures defining energy absorption abilities for composites is different from structures made from traditional homogenous materials. (Saarela, O. Airasmaa, I. Kokko, J. Skrifvars, M. Komppa, V Komposiittirakenteet. Muoviyhdistys, Helsinki)

GOAL Energy absorption properties of sandwich laminates. Develop simplified spring force model to predict behaviour of laminate during slow, non-cutting, non- bending penetration. Test the model against results of tests made on 7 different Divinycell - glass fibre sandwich laminates. Test procedure: non-cutting, non-bending penetration test.

MATHEMATICAL MODEL Kinetic energy of a moving body: When the boat collides with the object, momentum is converted to velocity (v1) through the following function: The amount of energy absorbed by the composite can be found by integrating the force over distance: (I.S. Grant, W.R. Phillips 2001)

MATHEMATICAL MODEL Since the change in energy is known the equation can be seen as: Or when solving for the displacement of the collision into the foam: Assuming the laminates behave like a spring during a collision

FOAM CORES DIAB DIVINYCELL foam cores MaterialTensile strengthCompressive strength H2509,2 MPa6,2 MPa H1003,5 MPa2,0 MPa H80GS (grid-scored)2,5 MPa1,4 MPa P1502,45 MPa2,30 MPa H601,8 MPa0,9 MPa H45GS (grid-scored)1,4 MPa0,6 MPa P601,10 MPa0,55 MPa

H45GS H60

P60 P150

MAKING THE LAMINATES Bi-axial -45/45 E-glass fibre 430g, Atlac 580 AC 300 vinyl ester One shot lamination

SANDWICH PANEL Skin of fibres laminated on both sides of a foam core

TESTING LAMINATES Non-cutting Non-bending 13,5mm sphere Destructive test

TESTING LAMINATES H60 H100

TESTING LAMINATES

Straight line at beginning of graph. y-value can be related as spring constant k. reasonable to assume that a simple spring model to determine performance of foam cores in a collision situation.

CORRELATION OF MODEL TO CORES Relationship between the manufacturers stated compression and shear modulus values and the k –value derived from actual tensile tests exists for compressive modulus at a rate of 90,5%. In the case of shear modulus the rate of occurrence is 88,34%.

CORRELATION OF MODEL TO CORES

MODEL AT WORK The tests imply that the cores exhibit performance that can be modelled in a simple way. Practical application of results to find out the max. allowable speed: z value is mass-ratio:

MODEL AT WORK BUSTER X COLLIDING WITH SEA CONTAINER

MODEL AT WORK NAUTOR SWAN 60 COLLISION WITH SEA CONTAINER H250P150H100H80GSP60H60H45GS k725,68547,50530,24507,15460,18446,62362,31 k*(x*100)* , , , , , , ,00 ∆E36,2827,3826,5125,3623,0122,3318,12 m/s0,080,07 0,06

MODEL AT WORK H250P150H100H80GSP60H60H45GS k725,68547,5530,24507,15460,18446,62362,31 k*(x*100)* , , , , , , ,00 ∆E2 322, , , , , , ,39 m/s2,822,452,412,362,252,211,99 H250P150H100H80GSP60H60H45GS k725,68547,5530,24507,15460,18446,62362,31 k*(x*100)* , , , , , , ,00 ∆E2 322, , , , , , ,39 m/s2,061,791,761,721,641,611,45 Buster X colliding with Buster X Nautor Swan colliding with Buster X

DISCUSSION Performance of the laminate in a collision situation will change depending on the type of reinforcement, the resin and the way the laminate has been manufactured. Age, wear and conditions affect laminates. Laminates studied in this thesis had four layers of glass fibre on each side of the foam core. How do sandwich laminates behave with different reinforcement and matrix materials?

DISCUSSION When a cut or groove extends through the foam connecting the top and bottom skin the compression properties of the laminate change. Tests that simulate a cutting, glancing collision could be advisable to produce information on how the foam and fibre laminates behave.

DISCUSSION So far there are few reliable ways to pre- determine the final strength of a composite laminate in a way that would allow for estimates between varying amounts of fibre layers. Future research into developing systems that could be fibre and resin specific in determining the resulting strength of the structure could be useful.

CONCLUSIONS Relationship between the datasheet properties of compressive and shear modulus of most of the foam core materials tested and their actual energy absorbing capabilities shown to exist. Sandwich laminates display a reasonably straight force over distance line before the end of elastic deformation occurs. This means that these laminates contain a section of their behaviour under load that can, within reason be modelled using an applied spring model equation.

QUESTIONS