Cruciform specimens biaxial extension performance relationship to constitutive identification

Main desired features of biaxial tests are: uniformity of stresses and strains; high strain levels in gauge areas; reliable constitutive parameters identification. Despite cruciform specimen suitability to modern tensile devices, standard testing techniques are still debated because of difficulties in matching these demands. This work aims at providing rational performance objectives and efficient cruciform specimens shapes in view of constitutive parameter fitting. Objective performance is evaluated along particular lines lying on principal directions in equibiaxial tensile tests. A rich specimen profile geometry is purposely optimized in silico by varying cost function and material compressibility. Experimental tests, monitored via digital image correlation, are carried out for validation. New shapes are designed and tested in a biaxial tensile apparatus and show to perform better than existing ones. Parameter fitting is efficiently performed by only exploiting full field strain measurements along lines. Small gauge areas and small fillet radii cruciform specimens get closer to the ideal behavior. For constitutive parameters identification in two-dimensional tensile experiments, data analysis on gauge lines deformation suffices

Analysis of residual stresses in thermoelastic multilayer cylinders

The topic faced here is the modeling of an axisymmetric multilayer structure. An exact analytical formulation is proposed in the framework of the plane strain problem for a cylinder encircled by annular layers. Isotropic linear thermoelastic materials constitute the body. Perfect and imperfect contacts between the layers are made available for the analysis. The derived exact solution is compared to finite element simulations. Numerical applications are shown in order to study the dependency of the residual stress distribution on the constituent material properties during a cooling process. The role of residual stresses in brittle materials, particularly ceramics, is discussed

Influence of fracture criteria on dynamic fracture propagation in a discrete chain

The extent to which time-dependent fracture criteria affect the dynamic behavior of fracture in a discrete structure is discussed in this work. The simplest case of a semi-infinite isotropic chain of oscillators has been studied. Two history-dependent criteria are compared to the classical one of threshold elongation for linear bonds. The results show that steady-state regimes can be reached in the low subsonic crack speed range where it is impossible according to the classical criterion. Repercussions in terms of load and crack opening versus velocity are explained in detail. A strong qualitative influence of history-dependent criteria is observed at low subsonic crack velocities, especially in relation to achievable steady-state propagation regimes

Stability and sensitivity analysis of bird flapping flight

This paper investigates stability analysis of flapping flight. Due to time-varying aerodynamic forces, such systems do not display fixed points of equilibrium. The problem is therefore approached via a limit cycle analysis based on Floquet theory. Stability is assessed from the eigenvalues of the Jacobian matrix associated to the limit cycle, also known as the Floquet multipliers. We developed this framework to analyze the flapping flight equations of motion of a bird in the longitudinal plane. Such a system is known to be not only non-linear and time-dependent, but also driven by state-dependent forcing aerodynamic forces. A model accounting for wing morphing under prescribed kinematics is developed for generating realistic state-dependent aerodynamic forces. The morphing wing geometry results from the envelope of continuously articulated rigid bodies, modeling bones and feather rachises, and capturing biologically relevant degrees of freedom. A sensitivity analysis is carried out which allows studying several flight configurations in trimmed state. Our numerical results show that in such a system one instability mode is ubiquitous, thus suggesting the importance of sensory feedback to achieve steady-state flapping flight in birds. The effect of wingbeat amplitude, governed by the shoulder joint, is found to be crucial in tuning the gait towards level flight, but marginally affects stability. In contrast, the relative position between the wing and the center of mass is found to significantly affect the values of Floquet multipliers, suggesting that the distribution of pitching moment plays a very important role in flapping flight stability

SARS-CoV-2 Infection Incidence and Outcome Before and After Full Vaccination in Patients With Monoclonal Gammopathy of Undetermined Significance

N