A novel technical finding is proposed based on the analytical study of the underlying conservative system of a small mass nonlinear vibration absorber coupled with a main structure. For the system with linear damping under impulsive excitation, a result is obtained that the initial energy for inducing maximum dissipation of energy in the nonlinear attachment is inversely proportional to the cubic stiffness. The technical point coincides with massive numerical simulations precisely. This relationship between the cubic stiffness and the initial conditions facilitates the tuning of a nonlinear vibration absorber for realizing optimal targeted energy transfer.
For the problem on the deviation of actual measurement values between different network positions of visual measurement network system , so present the weighted data fusion algorithm . To distribute the weight coefficients according to the stability of eigenvector and fuse the coordinates , finally get the ultimate expression of fusion estimate. The experiment results present the maximum absolute tolerance of the fusion results is 0.039mm via the weighted data fusion algorithm, the maximum one via traditional data fusion algorithm of the center of point set is 0.056mm , Repeatedly measure 50 times , compared with the traditional algorithm, proposed weighted data fusion algorithm has much better precision and better stability.
Most of imaging algorithms used in guided wave arrays share the same assumption that the signal scattered from defects will propagate uniformly in all directions. However, some recent researches on scattering properties of guided wave in defects demonstrate that the scattered signal is un-uniform even for a circular hole. Scattering properties of defects were studied and effects of sensors distribution strategies were presented in this paper. A 3D FE model was employed to study the sensor arrangement method and two basic imaging methods ellipse and hyperbola algorithm was used. Experiment was implemented in a 3mm aluminum plate with piezoelectric elements. Results show that for crack-like defects and through-hole, both ellipse and hyperbola imaging algorithms were valid. The number and position of transducers affect the accuracy of crack imaging. To detecting different kinds of defect the preferable array arrangement should be set according to the scattering characterization of defect.
Recently, hydroforming has paid dividends in composite forming due to its uniform pressure distribution, which helps in reducing the delamination defects. Considering the need to develop an appropriate criterion for evaluating the formability of FMLs, inspired by sheet metal forming and testing, the uniform pressure loading test was adopted to characterize the formability of semi-cured FMLs by forming limit curve ( FLC). In this paper, both theoretical analysis models considering and ignoring the tangential cohesive effect were established, and the stress expression of the critical zone was given. The results show that the tangential cohesive stress demonstrates a non-negligible influence on the FLC. A new form of comprehensive FLC was given by defining global equivalent strain and global strain ratio and analyzed by the finite element method. In addition, the numerical simulation model and the experimental parameters were verified. A simplified Hashin criterion was proposed and developed into the numerical simulation as a subroutine based on theoretical analysis. Parameters such as blank holder pressure, pressure rate, and temperature were considered both in experiments and simulation. Only fiber stretching damage was distinguished in the cross, single, and arc crack but no wrinkling. As predicted theoretically, a lower forming limit is expected when FMLs are subjected to greater tangential cohesive stress. Finally, with the help of numerical simulation, the influence of different boundary conditions on the comprehensive FLC was studied. Instead of a simple evaluation of FMLs, this comprehensive FLC could be used directly to optimize hydroforming processes in the engineering field.
With the development of visual measurement system , the visual measurement system of single camera which applied in the imaging theory of optical feature points , it has been widespread used in the modern production . Due to the limit of the environment in scene , the visual measurement system of single camera could not measure the shield between the measured objects each other . Focus on this problem , present a kind of the the knowledge of measurement network based on the visual measurement of single camera , set up the measurement network system via the multi-control points . Measure the optical feature points in every network control point via the visual measurement system of single camera; Normalize the measured coordinates into the same world coordinate system , then get the global data , and achieve the overall measurement ; Apply in the three coordinate measuring machine(CMM) to have the simulation experiment , the result indicates that the maximum absolute tolerance between the normalization coordinates via the center of point set and the ones measured by CMM directly is 0.058mm ; But the one between the coordinate repeatedly measured at the position of one network control point is 0.066mm ; So the data normalization has the advantage of more high precision .
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