Redundancy and robustness of brittle laminated plates. Overlooked aspects in structural glass

It is a consolidated belief that the reliability of brittle plates is increased using laminated layers instead of a monolith: redundancy permits stress redistribution after partial breakage. To quantify this effect, the retro-cumulative function of plate strength is calculated for inflected laminates with a variable number of plies using the failure modes approach. The material is elastic perfectly-brittle and its strength may be characterized by different statistics, implying either volume-size-effect, area-size-effect, or no-size-effect. The plate is analysed in limit conditions for what concerns the capability of the adhesive layers to transfer shear stresses. Robustness is discussed by assuming that an accidental event may break one of the plies. The type of size-effect plays a decisive role. Under the same maximum tensile stress in the sound state, lamination is always beneficial only for volume-size-effect. For area-size-effect, the negative effect of the new surface from lamination is counterbalanced by stress redistribution only for the lower quantiles of the strength distribution. The same is true under an accidental event. With no-size-effect, the gain from lamination is again appreciable only at low failure probabilities. These findings raise questions about the positive effects of lamination for structural glass, strongly characterized by an area size effect.