Bone and other natural material exhibit a combination of strength and toughness that far exceeds that of synthetic structural materials. Bone's toughness is a result of numerous extrinsic and intrinsic toughening mechanisms that operate synergistically at multiple length scales to produce a tough material. At the system level however no theory or organizational principle exists to explain how s...

In 1995, Brouwer proved that the toughness of a connected k-regular graph G is at least k/λ − 2, where λ is the maximum absolute value of the non-trivial eigenvalues of G. Brouwer conjectured that one can improve this lower bound to k/λ − 1 and that many graphs (especially graphs attaining equality in the Hoffman ratio bound for the independence number) have toughness equal to k/λ. In this pape...

A missing cornerstone in the development of tough micro/nano fibre systems is an understanding of the fibre failure mechanisms, which stems from the limitation in observing the fracture of objects with dimensions one hundredth of the width of a hair strand. Tensile testing in the electron microscope is herein adopted to reveal the fracture behaviour of a novel type of toughened electrospun poly...

Microdamage resulting from fatigue or 'wear and tear' loading contributes to bone fragility; however, the full extent of its influence is not completely understood. Linear microcracks (∼50-100 μm) and diffuse damage (clusters of sublamellar-sized cracks) are the two major bone microdamage types, each with different mechanical and biological consequences. Healthy bone, due to its numerous micros...

In previous studies, enamel showed indications to occlude small cracks in-vivo and exhibited R-curve behaviors for bigger cracks ex-vivo. This study quantifies the crack tip's toughness (K(I0),K(III0)), the crack's closure stress and the cohesive zone size at the crack tip of enamel and investigates the toughening mechanisms near the crack tip down to the length scale of a single enamel crystal...

Bone is more difficult to break than to split. Although this is well known, and many studies exist on the behaviour of long cracks in bone, there is a need for data on the orientation-dependent crack-growth resistance behaviour of human cortical bone that accurately assesses its toughness at appropriate size scales. Here, we use in situ mechanical testing to examine how physiologically pertinen...

Delamination is a predominant failure mechanism in composite structures. In the present study, double cantilever beam tests were performed to investigate the effects of temperature and fiber orientation on the Mode I interlaminar fracture toughness, G I , of carbon fiber-reinforced epoxy composites, T800H/#3631. The values of G I for three kinds of laminates, [0 12 //0 12 ], [22.5/-22.5/0 8 /-2...

Fracture toughness, strength, and elastic modulus of poly(methyl methacrylate) (PMMA)and poly(buty1 methacrylate) (PBMA)-impregnated alumina ceramics were measured as a function of polymer volume fraction, mean polymer particle size, and interfacial bonding between the polymer and ceramic. Fracture toughness was found to increase with increasing polymer volume fraction and decreasing polymer pa...

Variations in physical toughness between muscles and animals are a function of growth rate and extend of collagen type I and III. The current study was designed to investigate the ability of growth rate, collagen concentration, collagen synthesizing and degrading genes on two different fibroblast cells derived from Hanwoo m. longissimus dorsi (LD) and semimembranosus (SM) muscles. Fibroblast ce...

This study uses observations of mechanisms from previous work (the “undamaged cone”, toughness and extent of permanent out-of-plane deformation) to examine parametrically their effects on residual compression after impact (CAI) strength using finite element models. In previous experimental work, tougher material systems exhibited up to 30% greater CAI strength for a given damage area. Based on ...