4_1: UNIDIRECTIONAL FIBERS CREEP - BAMBOO Bamboo is made mostly of longitudinal cellulose fibers; under bending, the weak links connecting parallel fibers move and allow shear, absorbing energy. The fibers on the external side of the curved beam started to fail by traction, while some fibers in the inner side buckled by compression in a curly pattern. The beam as whole is still in one piece and holding. The strength and flexibility of bamboo has been exploited by human engineering since prehistory and bamboo products are still manufactured in industrial proportions. Subject: Bamboo chopstick bent under hot steam. Likely from a Phyllostachys genera plant. Beam section 5x6 mm, total length 220mm, min radius of curvature 25mm. Lens: Macro 90mm f/16 Theme 4: TOUGHNESS OF COMPOSITES Development of artificial composite materials is today in a golden age; the extreme strength of artificial fibers allows us to fabricate new materials with unprecedented performances. However, when it comes to impact resistance, toughness and flexibility, we still have to rely on bulk materials like metals, plastics and elastomers. Our composites are not yet mature, performing way below the potential of their constituents. The positioning of the reinforcement fibers, their interlocking, the adhesion with the matrix, the control of cracks growth, those are the critical factors that can and need to be improved. Biological tissues instead, being built up from the molecular level, show an high degree of refinement in their micro and mesoscopic structure, resulting in lightweight and extremely tough materials. The images presented try to convey in a visual manner some solutions hidden in natural materials on how they fail progressively while holding structural integrity.