failure. The substrate was determined to be stainless steel, indicating that it came from a refrigerated store or similar location. Although little time remained to embark on a thorough experimental programme revolving around this panel specifically, with the gained understanding of the nature of the adhesion now established for the sandwich panels it is possible to have an understanding of the causes of these blisters. This type of failure is the most problematic for the manufacturer as it occurs with products already in use. As noted in the literature temperature variations in use can cause stresses in the materials which have been linked to the appearance of the blister failure. Although it is unlikely to cause an issue regarding safety or the structural integrity of the building, or even affect the thermal insulating properties, customers for this product consider the unsightly appearance of these blisters, which are very apparent on the outside surface of the building, unacceptable. Experimental method Introduction Shown in Figure 91 is the panel as received, it was approximately 2.5 x 1m. It demonstrates the area and appearance of the blistered region. It is important to note that this failure occurs on the exterior face of the building as this implies that this is the blister has occurred to the side which the foaming polyurethane is applied. Figure 91 Received blister failed panel Sample preparation When this panel was cut by hacksaw there was an obvious stress relieving effect in the substrate as it straightened (from being bent to form the blister) and delaminated from the foam bulk. This can be seen in Figure 92. Also demonstrated is the detailing of the formed substrate to which the foam was applied. As can be seen it is complex with a design that obstructs the flow of a fluid.
failure. The substrate was determined to be stainless steel, indicating that it came from a refrigerated store or similar location. Although little time remained to embark on a thorough experimental programme revolving around this panel specifically, with the gained understanding of the nature of the adhesion now established for the sandwich panels it is possible to have an understanding of the causes of these blisters. This type of failure is the most problematic for the manufacturer as it occurs with products already in use. As noted in the literature temperature variations in use can cause stresses in the materials which have been linked to the appearance of the blister failure. Although it is unlikely to cause an issue regarding safety or the structural integrity of the building, or even affect the thermal insulating properties, customers for this product consider the unsightly appearance of these blisters, which are very apparent on the outside surface of the building, unacceptable. Experimental method Introduction Shown in Figure 91 is the panel as received, it was approximately 2.5 x 1m. It demonstrates the area and appearance of the blistered region. It is important to note that this failure occurs on the exterior face of the building as this implies that this is the blister has occurred to the side which the foaming polyurethane is applied. Figure 91 Received blister failed panel Sample preparation When this panel was cut by hacksaw there was an obvious stress relieving effect in the substrate as it straightened (from being bent to form the blister) and delaminated from the foam bulk. This can be seen in Figure 92. Also demonstrated is the detailing of the formed substrate to which the foam was applied. As can be seen it is complex with a design that obstructs the flow of a fluid.
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