Free vibration of functionally graded material beams with surface-bonded piezoelectric layers in thermal environment

Free vibration of statically thermal postbuckled functionally graded material （FGM） beams with surface-bonded piezoelectric layers subject to both temperature rise and voltage is studied. By accurately considering the axial extension and based on the Euler-Bernoulli beam theory, geometrically nonlinear dynamic governing equations for FGM beams with surface-bonded piezoelectric layers subject to thermo-electro- mechanical loadings are formulated. It is assumed that the material properties of the middle FGM layer vary continuously as a power law function of the thickness coordinate, and the piezoelectric layers are isotropic and homogenous. By assuming that the amplitude of the beam vibration is small and its response is harmonic, the above mentioned non-linear partial differential equations are reduced to two sets of coupled ordinary differential equations. One is for the postbuckling, and the other is for the linear vibration of the beam superimposed upon the postbuckled configuration. Using a shooting method to solve the two sets of ordinary differential equations with fixed-fixed boundary conditions numerically, the response of postbuckling and free vibration in the vicinity of the postbuckled configuration of the beam with fixed-fixed ends and subject to transversely nonuniform heating and uniform electric field is obtained. Thermo-electric postbuckling equilibrium paths and characteristic curves of the first three natural frequencies versus the temperature, the electricity, and the material gradient parameters are plotted. It is found that the three lowest frequencies of the prebuckled beam decrease with the increase of the temperature, but those of a buckled beam increase monotonically with the temperature rise. The results also show that the tensional force produced in the piezoelectric layers by the voltage can efficiently increase the critical buckling temperature and the natural frequency.

Hybrid Additive Manufacturing of Forming Tools

Additive manufacturing(AM)is widely used in the automotive industry and has been expanded to include aerospace,marine,and rail.High flexibility and the possibility of manufacturing complex parts in AM motivate the integration of additive manu-facturing with classical forming technologies,which can improve tooling concepts and reduce costs.This study presents three applications of this integration.First,the possibility of successful utilization of selective laser melting for manufacturing extrusion tools with complex cooling channels and paths for thermocouples is reported,leading to significantly reduced inner die temperatures during the extrusion process.Second,sheet lamination is integrated with laser metal deposition(LMD)to manufacture deep-drawing dies.Promising results are achieved in reducing the stair step effect,which is the main challenge in sheet lamination,by LMD and following post-processing such as milling,ball burnishing,and laser polishing.The new manufacturing route shows that LMD can economically and efficiently reduce the stair step effect and omit the hardening step from the conventional manufacturing process route.Finally,LMD is used to manufacture a hot stamping punch with improved surface roughness by ball burnishing and near-surface complex cooling channels.The experimental results show that the manufactured punch has lower temperatures during hot stamping compared with the conventionally manufactured punch.This study shows the successful integration of AM processes with classical forming processes.

Correlation between microstructure and tensile behavior of metal–intermetallic laminate compound with different initial Ni foil thickness

Ni-base metal–intermetallic laminate composites were obtained from in situ reaction synthesis between Ni and Al foils by utilizing plasma activated sintering. The effects of Ni foil thickness on the microstructure and tensile properties of the composites were investigated. The results show that the phases forming during reaction synthesis are independent of the starting thickness of the Ni foils. However, thicker reacted layers are obtained in the samples fabricated from 100 lm Ni foils（Ni100） than those obtained in the samples from 50 lm Ni foils（Ni50）when treated at the same process. The tensile strength of Ni100 samples increases with the temperature increasing at the expense of ductility. Dissimilarly, Ni50 composites treated at higher temperatures exhibit enhanced strength and ductility. Both Ni50 and Ni100 laminate fracture in a similar mechanism. Cracking first occurs in the brittle intermetallic layers. These original cracks result in shear bands in Ni layers emitted from the crack tips, and thus producing local stress concentration, which initiates new cracks in adjacent intermetallic layers. The multiplication of cracks and shear bands leads to the failure of the laminates.