Mechanical metamaterials with engineered failure properties typically rely on periodic unit cell geometries or bespoke microstructures to achieve their unique properties. We demonstrate that intelligent use of disorder in metamaterials leads to distributed damage during failure, resulting in enhanced fracture toughness with minimal losses of strength. Toughness depends on the level of disorder, not a specific geometry, and the confined lattices studied exhibit a maximum toughness enhancement at an optimal level of disorder. A mechanics model that relates disorder to toughness without knowledge of the crack path is presented. The model is verified through finite element simulations and experiments utilizing photoelasticity to visualize damage during failure. At the optimal level of disorder, the toughness is more than 2.6× of an ordered lattice of equivalent density.

The process of material cutting emerges from a series of nonlinear phenomena including frictional contact, plastic deformation, and fracture. While cutting dominated by shear deformation is of interest to achieve a smooth material removal and a high-quality surface finish, the fracture-induced chip breaking is of equal importance to prevent the formation of long chips. Here we show that discrepant observations and predictions of these two distinct cutting mechanisms can be reconciled into a unified framework. A simple analytical model is developed to predict the mechanism of chip formation in a homogeneous medium as a function of work piece intrinsic material properties, tool geometry, and the process parameters. The model reveals the existence of a critical depth of cut, below which the chip formation is gradually progressed by plastic deformation in the shear plane, and above which chips break off by abrupt crack propagation. The models’ prediction is validated by systematic in situ orthogonal cutting experiments and literature data for a wide range of materials over multiple length scales.

Macro and microstructural damage was studied in typical glass fibre-reinforced polymer laminates with two types of coating systems – (a) isophtalic gel coat: pure or mixed with SiO₂ nanoparticles 5 wt% (5%N) or 10 wt% (10%N) and (b) a two-layer coating system: urethane-modified vinyl ester-based gel coat and additional polyester barrier coat layer. Accelerated tests were performed at 50℃ for 50 days for specimens with nanoparticle-modified gel and for the specimens with or without a barrier coat. Long-term ageing behaviour at 23℃ was assessed for the two-layer systems. Nanoparticle-reinforced specimens (10%) showed some advantage over ‘barrier coat systems' in terms of blister incubation time (16 and 13 days, respectively), while for 5% and 0% nanoparticles, blister incubation times were 3 and 7 days, respectively. Round and/or acicular blisters were observed on the examined surfaces. The varying size, shape and distribution of blisters was illustrated by macro and micrographs showing various failure modes associated with surface blisters.