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Journal ArticleDOI

Polygonal deformation of a metallic foil subjected to impact by an axisymmetric indenter

TL;DR: In this article, a stack consisting of layers of soft elastomer and thin metallic film is subjected to low intensity impact by releasing an axisymmetric spherical indenter from a vertical height, the foils buried within the stack undergoes large deformation and fracture.
Abstract: When a stack consisting of layers of soft elastomer and thin metallic film is subjected to low intensity impact by releasing an axisymmetric spherical indenter from a vertical height, the foils buried within the stack undergoes large deformation and fracture. The shape of the deformed area nevertheless remains circular, its radius first increases with the depth from the surface of the stack and then decreases. In contrast, here we show that the symmetry of the deformed area breaks down when instead of a smooth elastomeric layer, one with topographical patterns is used in the stack. The metallic foil deforms through a polygonal area. The size and shape of the polygonal area vary with the flexibility of foil, geometry and dimension of the patterns and the intensity of the impact. For example, for one elastomeric layer decorated with pillars arranged in a square array, the damaged area turns rectangular to hexagonal and then to octagonal with increasing severity of impact, very much similar to polygo...
References
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PatentDOI
06 Apr 2012-Science
TL;DR: In this article, the authors present stretchable and printable semiconductors and electronic circuits capable of providing good performance when stretched, compressed, flexed, or otherwise deformed.
Abstract: The present invention provides stretchable, and optionally printable, semiconductors and electronic circuits capable of providing good performance when stretched, compressed, flexed or otherwise deformed. Stretchable semiconductors and electronic circuits of the present invention preferred for some applications are flexible, in addition to being stretchable, and thus are capable of significant elongation, flexing, bending or other deformation along one or more axes. Further, stretchable semiconductors and electronic circuits of the present invention may be adapted to a wide range of device configurations to provide fully flexible electronic and optoelectronic devices.

1,673 citations

Journal ArticleDOI
TL;DR: An operative treatment of an articular surface injury must produce better long-term joint function than would be expected if the injury was left untreated or treated by irrigation and debridement alone.
Abstract: The acute and repetitive impact and torsional joint loading that occurs during participation in sports can damage articular surfaces causing pain, joint dysfunction, and effusions. In some instances, this articular surface damage leads to progressive joint degeneration. Three classes of chondral and osteochondral injuries can be identified based on the type of tissue damage and the repair response: (1) damage to the joint surface that does not cause visible mechanical disruption of the articular surface, but does cause chondral damage and may cause subchondral bone injury; (2) mechanical disruption of the articular surface limited to articular cartilage; and (3) mechanical disruption of articular cartilage and subchondral bone. In most instances, joints can repair damage that does not disrupt the articular surface if they are protected from additional injury. Mechanical disruption of articular cartilage stimulates chondrocyte synthetic activity, but it rarely results in repair of the injury. Disruption of subchondral bone stimulates chondral and bony repair, but it rarely restores an articular surface that duplicates the biologic and mechanical properties of normal articular cartilage. In selected patients, surgeons have used operative treatments including penetrating subchondral bone, soft tissue grafts, and cell transplants and osteochondral autografts and allografts to restore articular surfaces after chondral injuries. Experimental studies indicate that use of artificial matrices and growth factors also may promote formation of a new joint surface. However, an operative treatment of an articular surface injury that will benefit patients must not just provide a new joint surface, it must produce better long-term joint function than would be expected if the injury was left untreated or treated by irrigation and debridement alone. Therefore, before selecting a treatment for a patient with an articular cartilage injury, the surgeon should define the type of injury and understand its likely natural history.

568 citations

Journal ArticleDOI
TL;DR: The ability of surface wrinkling to yield new insights into particularly challenging materials systems such as ultrathin films, polymer brushes, polyelectrolyte multilayer assemblies, ultrasoft materials, and nanoscale structured materials is highlighted.
Abstract: Surface instabilities in soft matter have been the subject of increasingly innovative research aimed at better understanding the physics of their formation and their utility in patterning, organizing, and measuring materials properties on the micro and nanoscale. The focus of this Review is on a type of instability pattern known as surface wrinkling, covering the general concepts of this phenomenon and several recent applications involving the measurement of thin-film properties. The ability of surface wrinkling to yield new insights into particularly challenging materials systems such as ultrathin films, polymer brushes, polyelectrolyte multilayer assemblies, ultrasoft materials, and nanoscale structured materials is highlighted. A perspective on the future directions of this maturing field, including the prospects for advanced thin-film metrology methods, facile surface patterning, and the control of topology-sensitive phenomena, such as wetting and adhesion, is also presented.

496 citations

Journal ArticleDOI
TL;DR: In this paper, the authors investigate the low velocity impact load level at which a composite laminate will delaminate and find that a sudden load drop occurs due to specimen stiffness loss as a result of laminate level damage.
Abstract: An investigation of the low velocity impact load level at which a composite laminate will delaminate is presented. The delamination threshold load is described as the load level, obtained from the load–time history or load–displacement plot, at which a sudden load drop occurs due to specimen stiffness loss as a result of laminate level damage. Approximately 500 low velocity impact load–time histories from the Air Force Research Laboratory (AFRL) Low Velocity Impact Database are used to investigate the delamination threshold load. The database contains laminate impact test data for graphite/epoxy (AS4/3501-6), graphite/PEEK (AS4/APC-2), and graphite/BMI (IM7/5260) material systems. The delamination threshold load observations are compared to C-scan damage measurements of impacted specimens to determine if the sudden load drop corresponds to delamination development.

477 citations

Journal ArticleDOI
TL;DR: In this paper, the authors identified the mechanism of elastic stretchability in the films with micro-cracks and showed that the metal film experiences only small strains and deforms elastically without suffering fatigue.
Abstract: Gold films on an elastomeric substrate can be stretched and relaxed reversibly by tens of percent. The films initially form in two different structures, one continuous and the other containing tribranched microcracks. We have identified the mechanism of elastic stretchability in the films with microcracks. The metal, which is much stiffer than the elastomer, forms a percolating network. To accommodate the large elongation of the elastomeric substrate, the metal network twists and deflects out of the plane but remains bonded to the soft substrate. Consequently, the metal film experiences only small strains and deforms elastically without suffering fatigue.

431 citations