Simulation and automation of aluminium panel shot peen forming

We present a methodology for automated forming of metal plates into freeformshapes using shot peening. The methodology is based on a simulation softwarethat computes the peening pattern and simulates the effect of its application.The pattern generation requires preliminary experimental characterizationof the treatment. The treatment is applied by a shot peening robot. The program for the robot is generated automatically according to the peening pattern. We validate the methodology with a series of tests. Namely, we form nine aluminum plates into doubly curved shapes and we also shape model airplane wing skins. The article describes the complete workflow and the experimental results.

Damage quantification of aluminum plates using SC-DTW method based on Lamb waves

Lamb waves were utilized to quantify micro-crack damage in aluminum plates, and the scattering and mode conversion of Lamb waves passing through cracks were analyzed. The dynamic time warping (DWT) method was used to match and compare each Lamb wave time series that represented different damage degrees. The matching difference between the damaged plate and undamaged plate was taken as a marker to measure the damage degree of the workpiece. At the same time, due to the pathological alignment of traditional DTW methods, the shape context (SC) profile recognition method was introduced to optimize the algorithm for calculating the distance between sampling points in the DTW method and solve the pathological alignment problem. Finally, the SC-DTW method based on Lamb waves was verified by the finite element simulation model and bending test of aluminum plates. The results showed that the method was feasible for quantifying the damage degree of aluminum plates and had a great advantage in the analysis and processing of time series in low-sampling frequency and high-noise scenarios.

An Infrared DoLP Model Considering the Radiation Coupling Effect

The polarization degree of objects in the marine background are affected by infrared radiation from sea surface. Taking into account the radiation coupling effect (RCE), a degree of linear polarization (DoLP) model is deduced. The DoLP of painted aluminum plates at different observation angles are simulated. The simulation results show the trend of the DoLP of the object decreases first and then increases as the observation angle θO, with the minimum value at θO=53∘. Nevertheless, we get a monotonically increasing trend and the minimum value is at θO=0∘ without considering RCE. The experimental results accord closely with those of the simulation with RCE. This conclusion is useful for the polarization detection and identification of infrared objects in the marine background.

Influence of Cold Rolled Deformation Degree and Heating Rates on Crystallite Dimension and Recrystallization Fraction of Aluminum Plates

In order to study the microstructure evolution rule of pure aluminum plates during different cold-rolled (CR) deformation degrees and annealing processes, samples with aCR deformation of 50~85%, heating rates of 60~100 °C/min and annealing at the target temperature of 350~500 °C were investigated. The microstructure, crystallite dimension and grain boundary characteristics were characterized by the methods of polarizing microscope (PM) and electron backscattered diffraction (EBSD). The results showed that the crystallite dimension of the initial state was 102 μm and ends up completely broken with an increase in the CR deformation degree. When the CR deformation increases to 85%, the deformed micro-bands were very small, with a band spacing of 5~10 μm. At this time, the grain distortion is more serious, there are more high-density grain defects, such as dislocations, and there is a high deformation of the storage energy, which is the energy preparation for the subsequent finished products to withstand the annealing process. The recrystallization fraction was higher with an increase in annealing temperature. After completed recrystallization, the grains showed an equiaxed shape. Orientation imaging and misorientation angle analysis showed that the red-oriented grains of the (001) plane, which had preferred nucleation, recrystallization and rapid grain growth. Final grains of the completed recrystallization are relatively coarse. Under the same deformation, the average crystallite dimension of the recrystallized grains decreases with an increase in annealing heating rate.

Finite Element Analysis and Preliminary Dynamic Tests of Laboratory Bridge Model

A preliminary dynamic test of a two-span continuous girder bridge is reported in this paper, including the design specifications, the numerical model, and the modal identification result. This laboratory bridge is made of aluminum plates and connected via bolts. The finite element method is applied to build a numerical model of the bridge to aid the design and test plan. Several ambient vibration tests are conducted to extract the modal parameters, e.g., modal frequencies, damping ratios, and mode shapes, of the constructed bridge, and the Bayesian FFT algorithm is used for modal identification. We compare the identified results with those predicted by the finite element model and vary the magnitude of load to investigate its potential influence on the modal parameters. Damage cases by loosening structure members are also considered, and significant changes are observed in modal frequencies. The constructed model will be used as a benchmark for damage identification, model updating, and condition assessment, etc.

Application of Electron Beam Welding Technique for Joining Ultrafine-Grained Aluminum Plates

The present study is the first attempt to join ultrafine-grained materials by electron beam welding. The aim of the study was to check the feasibility and effectiveness of this type of welding for thermally unstable materials. The results obtained are of high interest, while the welding did cause a decline in mechanical properties, the results were comparable to those obtained using solid-state welding, but with a significant advantage of narrower fusion- and heat-affected zones.