Finite element analysis of stress and strain distributions in mortise and loose tenon furniture joints

We studied the effect of loose tenon dimensions on stress and strain distributions in T-shaped mortise and loose tenon （M＆amp;LT） furni-ture joints under uniaxial bending loads, and determined the effects of loose tenon length （30, 45, 60, and 90 mm） and loose tenon thickness （6 and 8 mm） on bending moment capacity of M＆amp;LT joints constructed with polyvinyl acetate （PVAc） adhesive. Stress and strain distributions in joint elements were then estimated for each joint using ANSYS finite element （FE） software. The bending moment capacity of joints increased significantly with thickness and length of the tenon. Based on the FE analysis results, under uniaxial bending, the highest shear stress values were obtained in the middle parts of the tenon, while the highest shear elastic strain values were estimated in glue lines between the tenon sur-faces and walls of the mortise. Shear stress and shear elastic strain values in joint elements generally increased with tenon dimensions and corre-sponding bending moment capacities. There was consistency between predicted maximum shear stress values and failure modes of the joints.

Nano-refinement of the face-centered cubic Zr(Fe,Cr)_(2)secondary phase particles in Zircaloy-4 alloy via localized-shearing/bending-driven fracture under high-temperature compression

Nanoparticles are extensively introduced to improve the mechanical,physical,and chemical properties of alloys.In the present study,the underlying nano-refinement mechanisms of face-centered cubic Zr(Fe,Cr)_(2)secondary phase particles(SPPs)that precipitated in Zircaloy-4 alloy under high-temperature compression were investigated in detail by utilizing high-resolution transmission electron microscopy(HRTEM)and conventional TEM techniques.The frequently observed Zr(Fe,Cr)_(2)SPPs were incoherent with the matrix and exhibited brittle fracture behaviors without measurable plasticity.HRTEM observations revealed two mechanisms underlying the nano-refinement of incoherent micro-sized SPPs via localized shear fracture on{11¯2}SPP and nanoprecipitate-assisted bending fracture,respectively.The latter was,for the first time,found to occur when the movements of large SPPs were blocked by nanometer-sized SPP during alloy deformation.Accordingly,two force models were proposed to visualize their potential nano-refinement processes.The knowledge attained from this study sheds new light on the deformation behaviors of Zr(Fe,Cr)_(2)SPPs and their associated size refinement mechanisms under high-temperature compression,and is expected to greatly benefit the process optimization of zirconium alloys to achieve precipitate nano-refinement.

Design of ultrasonic elliptical vibration cutting system for tungsten heavy alloy

Nanoscale surface roughness of tungsten heavy alloy components is required in the nuclear industry and precision instruments.In this study,a high-performance ultrasonic elliptical vibration cutting(UEVC)system is developed to solve the precision machining problem of tungsten heavy alloy.A new design method of stepped bending vibration horn based on Timoshenko’s theory is first proposed,and its design process is greatly simplified.The arrangement and working principle of piezoelectric transducers on the ultrasonic vibrator using the fifth resonant mode of bending are analyzed to realize the dual-bending vibration modes.A cutting tool is installed at the end of the ultrasonic vibration unit to output the ultrasonic elliptical vibration locus,which is verified by finite element method.The vibration unit can display different three-degree-of-freedom(3-DOF)UEVC characteristics by adjusting the corresponding position of the unit and workpiece.A dual-channel ultrasonic power supply is developed to excite the ultrasonic vibration unit,which makes the UEVC system present the resonant frequency of 41 kHz and the maximum amplitude of 14.2μm.Different microtopography and surface roughness are obtained by the cutting experiments of tungsten heavy alloy hemispherical workpiece with the UEVC system,which validates the proposed design’s technical capability and provides optimization basis for further improving the machining quality of the curved surface components of tungsten heavy alloy.