![]() ![]() Both of these forces will induce the same failure stress, whose value depends on the strength of the material. If we don't take into account defects of any kind, it is clear that the material will fail under a bending force which is smaller than the corresponding tensile force. Conversely, a homogeneous material with defects only on its surfaces (e.g., due to scratches) might have a higher tensile strength than flexural strength. Therefore, it is common for flexural strengths to be higher than tensile strengths for the same material. However, if the same material was subjected to only tensile forces then all the fibers in the material are at the same stress and failure will initiate when the weakest fiber reaches its limiting tensile stress. ![]() When a material is bent only the extreme fibers are at the largest stress so, if those fibers are free from defects, the flexural strength will be controlled by the strength of those intact 'fibers'. In fact, most materials have small or large defects in them which act to concentrate the stresses locally, effectively causing a localized weakness. The flexural strength would be the same as the tensile strength if the material were homogeneous. Most materials generally fail under tensile stress before they fail under compressive stress Flexural versus tensile strength These inner and outer edges of the beam or rod are known as the 'extreme fibers'. At the outside of the bend (convex face) the stress will be at its maximum tensile value. At the edge of the object on the inside of the bend (concave face) the stress will be at its maximum compressive stress value. ![]() 1), it experiences a range of stresses across its depth (Fig. When an object is formed of a single material, like a wooden beam or a steel rod, is bent (Fig. 2 - Stress distribution through beam thickness University of Arizona Opto-Mechanical Papers Reference. "Flexure Mounts for High Resolution Optical Elements" (PPT). "Application of Flexure Structures to Active and Adaptive Opto-Mechanical Mechanisms" (PDF). "Three-degree-of-freedom flexure-based manipulator for high-resolution spatial micromanipulation". "Eliminating Underconstraint in Double Parallelogram Flexure Mechanisms". Additionally, special care must be taken to design the flexure to avoid material yielding or fatigue, both of which are potential failure modes in a flexure design. This makes flexures a critical design feature used in optical instrumentation such as interferometers.ĭue to their mode of action, flexures are used for limited range motions and cannot replace long-travel or continuous-rotation adjustments. Flexures are able to achieve much lower resolution limits (in some cases measured in the nanometer scale), because they depend on bending and/or torsion of flexible elements, rather than surface interaction of many parts (as with a ball bearing). It’s no secret that we think flexures are pretty cool, and we’ve featured a number of projects that leverage these compliant mechanisms to great effect. Additionally, conventional bearings or linear slides often exhibit positioning hysteresis due to backlash and friction. High precision alignment tasks might not be possible when friction or stiction are present. In the field of precision engineering (especially high-precision motion control), flexures have several key advantages. Using compound flexures, complex motion profiles with specific degrees of freedom and relatively long travel distances are possible. Since single flexure features are limited both in travel capability and degrees of freedom available, compound flexure systems are designed using combinations of these component features.
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