International audienceA strong correlation (R² >0.96) is found between machined surfaces and their fatigue limits. In a larger study, the four- point bending fatigue limit was determined on steel specimens milled with two different conditions, in two directions, with and without residual stresses relieved. Curvature analysis is shown here, based on Heron's formula, as a function of scale and position, on profiles extracted parallel to the direction of maximum tensile stress, from areal texture measurements. Several combinations of parameters are regressed linearly with the fatigue limits over a range of scales. The strongest correlations are found with the mean curvature plus two standard deviations, at a scale of 610μm. The correlation varies smoothly, although not monotonously, with respect to decreasing scale, with R² falling to zero at 100μm

The design of an optimal and versatile haptic device should enable human to achieve complex remote tasks in a safe and ergonomic environment. The paper presents a design strategy applied to the development of the Delthaptic, a new 6-DOF parallel haptic device. The Delthaptic is based on a coupled-parallel structure. It combines two Delta robots, linked to the two extremities of the customized ball-screw handle, to obtain its 6 degrees of freedom. The proposed haptic device provides a large and singularity-free workspace while keeping the benefits of parallel mechanisms. The design process first consists in a phase of structural design where the mechanical architecture is defined in order to meet requirements. During a second step, the parameters of this architecture are optimized by minimizing objective functions based on desired kinematic performances. Then, a generic procedure is proposed to select the actuation with respect to dynamic capability-based criteria as well as technological aspects. Actuators and transmission systems are chosen for the Delthaptic. A prototype of the haptic device is built to experimentally assess its mechanical functioning and check the design requirements.