Flexure hinge

Hinge Flex Life. An unusual and very interesting property of these resins is the flexural hinge life (see Table Vl)(2). 

Failure modes JS joint shear, CH column flexural hinging, FD FRP debonding Means computed with respect to T C... 

In this section some examples of precision engineering prototypes are presented that apply electrically heated shape memory actuators as driving elements. Further on flexure hinges of pseudo-elastic SM alloys will be presented. 

The micro gripper in Fig. 6.61 consists of a silicon structure with a dimension of approximately 7 x 4mm. In the open position the gripping jaws are 0.5 mm apart. The flexure hinges have a minimum thickness of 30 im. By machining a sputtered NiTi foil the SMA actuator has been realized with a minimum thickness of 30 pm. The gripping force averages by circa 11 mN. 

Fig. 6.62. CompUant spatial robot with 3 DOF and optimized design of a flexure hinge with 2 DOF [91]...

SM actuators may have very many different shapes and offer a variety of shape changes (i. e. actuator strokes). This property can be exploited so as to adapt the SM elements shape to the actuating task. As an application example, a miniature parallel gripper with electrically heated SM wires integrated into its mechanical structure was presented. Further on the performance of pseudo-elastic shape memory flexure hinges in parallel robots for micro-assembly tasks was shown. The future opportunity for thin-fllm SM actuators to drive micromechanical systems and devices was demonstrated by a miniature silicon gripper. 

Hesselbach, J. Raatz, A. Kunzmann, H. Performance of Pseudo-Elastic Flexure Hinges in Parallel Robots for Micro-Assembly Tasks. Annals of the CIRP, Vol. 53/1, (2004), pp. 329-332... 

Recently, another approach has been proposed by Asakawa et al Instead of using an acoustic wave, they used the deformation of a flexure hinge prepared in the cantilever holder to drive a cantilever. To illustrate the effect of the flexure drive mechanism, they made two cantilever holders with the same structure but made of different materials. One of them is made of SS316, and the other is made of polyetheretherketone (PEEK). The former is too hard to be deformed by the impulsive force generated by the vibration of the piezo actuator, while the latter is compliant enough to be deformed by that. This difference is illustrated in the simulation results obtained by the finite element method (Fig. 18.3a,b). 

The amplitude and phase curves obtained with the SS316 holder are distorted by the random peaks caused by the spurious resonances (Fig. 18.3c,e). On the contrary, such peaks are suppressed in the curves obtained with the PEEK holder (Fig. 18.3d,f). While the amplitude curve obtained by the PEEK holder shows almost an ideal response, the phase curve deviates from the ideal response. This is because of the linear phase delay caused by the finite delay time required for the deformation of the flexure hinge. However,... 

Figure 18.3 The 2D distribution of vibration amplitude in the simplifled model of the flexure hinge made of (a) SS316 and (b] PEEK simulated by the finite element method. Amplitude and phase curves obtained in water by the cantilever holder with the holder body made of (c, e] SS316 and (d, f] PEEK. The cantilever was driven with an excitation signal having an amplitude of 50, 100, or 150 mV. Note that the measured phase curves in (e] and (f] appear as a single curve due to their small dependence on the excitation amplitude. Abbreviation-. 2D, two dimensional.

Numerical Modeling of Masonry Infilled Reinforced Comer crashing (with flexural hinges in columns), (b)... 

Concrete Frame Buildings, Fig. 2 Typical damage Sliding along bed Joints (with flexural hinges in coliunns). 

Structural dements resist blast loads by developing an internal resistance based on material stress and section properties. To design or analyze the response of an element it is necessary to determine the relationship between resistance and deflection. In flexural response, stress rises in direct proportion to strain in the member. Because resistance is also a function of material stress, it also rises in proportion to strain. After the stress in the outer fibers reaches the yield limit, (lie relationship between stress and strain, and thus resistance, becomes nonlinear. As the outer fibers of the member continue to yield, stress in the interior of the section also begins to yield and a plastic hinge is formed at the locations of maximum moment in the member. If premature buckling is prevented, deformation continues as llic member absorbs load until rupture strains arc achieved. 

Physically, whenever a sample is pulled (tensile), squashed (compression), sliced in two (shear), flexed like the two sides of a hinge (flexureX or twisted (torsionX the ratio of the stress to the strain at any point in these motions is the tensile, compression, shear, flexure, or torsion modulus. 

---