Bonding strength, skin/core

A pressure of 25 psi and temperature of 175°C are required for 1 h to cure the epoxynylon adhesive. Because of their excellent filleting properties and high peel strength, epoxy-nylon adhesives are often used to bond aluminum skins to honeycomb core in aircraft structures. In these applications, climbing drum peel strengths in excess of 150 lb/in have been achieved. 

On the basis of these results, the sandwich moulding process was investigated by use of the controlled formation of chemical bonds for the improvement of the bond strength in the interface of the two components - the skin and the core component. The advantage of this process is a longer melt contact time during the mould filling period. 

After the tensile test no delamination between skin and core was observed in the fracture region, demonstrating the excellent bond strength (Fig. 17). 

No skin parts form deformed or stretched lips. The separation of the components by the peel test or by splitting with a wedge and the determination of the bond strength between skin and core component by measuring methods was not possible. 

It is reported that sandwich panels are being produced in the USA by pultrusion. In this process a plywood core is completely encased in a 3 mm thick glass polyester skin, resin penetrating the plywood during production to give increased bond strength and moisture resistance. 

Tensile Tests. The tensile strength of an adhesive joint is seldom reported in the adhesive supplier s literature because pure tensile stress is not often encountered in actual production. An exception to this is the tensile test of the bonds between the skins and core of a... 

One application is honeycomb sandwich construction that consists of thin high strength prepreg skins bonded to a thicker honeycomb, foam, or balsa core. The advantages are very low weight, high stiffness, durable, design freedom, and reduced production costs. 

---