Search results for "stiffne"
showing 10 items of 533 documents
Experimental Characterization of the Properties of Double-Lap Needled and Hybrid Joints of Carbon/Epoxy Composites
2015
The effect of through-thickness reinforcement by thin 1 mm steel needles (z-pins) on the static tensile strength of double-lap joints of a carbon/epoxy composite was investigated. Two types of joints—z-pinned and hybrid (including glued ones)—were considered. The joints were reinforced in the overlap region with 9, 25, or 36 z-pins. Comparing mechanical properties of the double-lap joints with the corresponding characteristics of their unpinned counterparts, the z-pins were found to be highly effective: the strength and stiffness of the pinned joints increased up to 300% and 280%, respectively. These improvements were due to a transition in the failure mechanism from debonding of the joint …
The Use of Atomic Force Microscopy in Determining the Stiffness and Adhesion Force of Human Dentin After Exposure to Bleaching Agents
2009
Introduction: Oxidant bleaching agents may induce several alterations on mineralized teeth tissues. Our aim is to study,at the ultrastructurallevel,mechanicalmodifications induced on dentin after exposure to different bleaching agents.Methods: Nanoindentation performed with atomic force microscopy was used to measure changes in dentin stiffness as well as the adhesion force between the tip and the tissue both in intertubular and peritubulardentin.Foreachspecimen,dentinlocalization, and bleaching agent, 100 independent nanoindentations were performed. Carbamide peroxide (30%) and hydrogenperoxide(35%) wereusedasbleaching agents. Results: A significant reduction of both stiffness and adhesion…
Lessons Learned on the Tensile and Bond Behavior of Fabric Reinforced Cementitious Matrix (FRCM) Composites
2020
Fabric Reinforced Cementitious Matrix (FRCM) composites represent an effective, compatible and cost-efficient solution for strengthening and retrofitting existing structures. A strong research effort was done to investigate the tensile and bond properties of these materials, as well as the overall behaviour of strengthened members. A Round Robin Test was organized by Rilem TC 250-CSM on 28 FRCM composites comprising basalt, carbon, glass, PBO, aramid and steel textiles, embedded in either cement, lime or geopolymer mortars, to collect an experimental dataset and define test protocols. This paper collects the outcomes of this study to highlight fundamental properties of FRCM and to investiga…
Constitutive Numerical Model of FRCM Strips Under Traction
2020
In this paper, the tensile behavior of Fiber Reinforced Cementitious Matrix (FRCM) strips is investigated through Finite Element (FE) models. The most adopted numerical modeling approaches for the simulation of the fiber-matrix interface law are described. Among them, the cohesive model is then used for the generation of FE models which are able to simulate the response under traction of FRCM strips tested in laboratory whose results are available in the technical literature. Tests on basalt, PBO and carbon coated FRCM specimens are taken into account also considering different mechanical ratios of the textile reinforcement. The comparison between FE results and experimental data allows val…
Experimental analysis and micromechanical models of high performance renewable agave reinforced biocomposites
2017
Abstract The present work deals with the experimental study of high performance biocomposites reinforced with optimized agave fibers, as well as the successive implementation of reliable micromechanical models that can be used at the design stage. In detail, systematical experimental analyses performed on biocomposites with epoxy or PLA matrix, have permitted to highlight that for short fibers biocomposites the reinforcing leads to a significant improvement of the matrix stiffness, whereas the particular damage mechanism based essentially on the matrix failure with consequent tensile failure of the fibers aligned with the applied load, does not allow to obtain an actual reinforcing of the m…
Structural factor in bending testing of fivefold twinned nanowires revealed by finite element analysis
2016
In this study, we performed finite element method simulations to investigate the effect of the structure on the elastic response of Ag and Au nanowires (NWs) with a fivefold twinned crystal structure in bending tests. Two different models of a pentagonal NW were created: a 'uniform model' having an isotropic continuous structure and a 'segmented model' consisting of five anisotropic domains. Two asymmetrical mechanical test configurations were simulated: cantilevered beam bending and 3-point bending. The dimensions of the NW, the test configurations, as well as the force and the displacement ranges were based on the previously obtained experimental data. The results of the simulations demon…
On nonlinear behavior in brittle heterogeneous materials
2006
Abstract Many modern fiber-reinforced composite materials are ‘brittle’, in the sense that their strain to failure under quasi-static loading is typically of the order of 1% when loaded in directions generally controlled by fiber fracture, and the energy-to-failure under the quasi-static loading curve is typically small. For this reason, analysis of these materials is typically done under assumptions of linear elasticity, usually for homogeneous materials or material layers in a laminate. This is in contrast to ‘ductile’ metal behavior in which elastic–plastic behavior is widely discussed. What is most remarkable is the fact that for long-term behavior, the situation is nearly reversed in m…
A comparative study of fatigue behaviour of flax/epoxy and glass/epoxy composites
2012
Experimental investigations on flax and glass fabrics reinforced epoxy specimens, i.e. FFRE and GFRE, submitted to fatigue tests are presented in this paper. Samples having [0/90]3S and [±45]3S stacking sequences, with similar fibre volume fractions have been tested under tension–tension fatigue loading. The specific stress-number of cycles to failure (S–N) curves, show that for the [0/90]3S specimens, FFRE have lower fatigue endurance than GFRE, but the [±45]3S FFRE specimens offer better specific fatigue endurance than similar GFRE, in the studied life range (<2 × 10^6). Overall, the three-stage stiffness degradation is observed in all cases except for [0/90]3S FFRE specimens, which prese…
Mechanical properties of Macadamia nutshell powder and PLA bio-composites
2016
AbstractA study on the mechanical properties of Macadamia nutshell powder/PLA bio-composites is presented in this paper. The effects of powder weight content, powder condition and processing methods are investigated with the aid of Design of Experiments. It is shown from the results that both the stiffness and strength are dependent on the weight content of Macadamia nutshell powders. The elastic modulus increases 9.8% when the Macadamia nutshell powder content is 40%. Both flexural and tensile strengths decrease with increasing Macadamia nutshell powder content. On average, when the Macadamia nutshell powder content is 40%, the decreases in the flexural and tensile strengths are 42 and 63%…
Viscoelastic properties of the Achilles tendon in vivo
2013
It has been postulated that human tendons are viscoelastic and their mechanical properties time-dependent. Although Achilles tendon (AT) mechanics are widely reported, there is no consensus about AT viscoelastic properties such as loading rate dependency or hysteresis, in vivo. AT force-elongation characteristics were determined from 14 subjects in an ankle dynamometer at different loading rates using motion capture assisted ultrasonography. AT stiffness and elongation were determined between 10 – 80% of maximum voluntary contraction (MVC) force at fast and slow loading rates. As subjects were unable to consistently match the target unloading rate in the slow condition, AT hysteresis was on…