We introduce a Monte-Carlo model for describing the factors controlling the tensile strength and elongation at break of multi-layer nonwoven sheets. Our results indicate that sheet fracture starts through partial delamination of the layers, which results in a change in slope of the stress-strain curve. Upon further straining, fiber strands in the layers start to break in shear and the process rapidly leads to catastrophic failure of the sheet. The importance of delamination strength, layer nonuniformities and fiber properties are discussed.