Structural Behavior of Digitally Fabricated Thin-Walled Timber Columns

This paper aims to investigate the structural behavior of digitally fabricated thin-walled timber sections with edge connectivity provided by integral mechanical press-fit joints. Experimental, numerical, and analytical investigations have been developed to accurately characterize the press-fit section behavior and their failure modes. Plywood fiber orientation, material thickness, and connection tightness are considered as potential factors that may affect the performance of the press-fit jointing system. Experimental testing of square hollow sections (SHSs) under uniaxial compressive loading showed failure of sections through both conventional crushing and novel pop-off bifurcation failures. Pop-off buckling behaviors were shown to be governed by the integral joint transverse stiffness and its magnitude relative to a critical edge stiffness value. Columns with joint transverse stiffness value less than the critical edge stiffness value exhibited pop-off failures. These joint stiffness values were obtained from testing of unloaded joints and were used to obtain accurate predictions of column failure modes. Joint stiffness values for loaded joints were then predicted with an interpolation model mapping axial strain to a tighter connection tolerance and these were used to obtain accurate estimations for column failure load in most of the tested column types. Comparative investigations showed thin-walled sections with integral joints only to be capable of matching the compressive capacities of glued sections, for instances where crushing governed. Similarly, the weight-specific compressive capacity of timber sections was found to be comparable to thin-walled steel sections when crushing governs.

An Investigation of Wear of Ball End Milling Cutter for High-Speed Milling of Hardened Cr12MoV Steel

The high-speed milling experiments on hardened Cr12MoV steel were carried out with ball end milling cutter of different edge parameters. The influences of helix angle and rake angle on tool life and surface roughness were focused on. Meanwhile, the impacts of edge parameters on cutting edge stiffness and flank wear were analyzed on the condition of high-speed milling. It carried out that smaller helix angle and negative rake angle selected during high speed milling can guarantee quality of surface manufactured as well as longer tool life.

Electromechanical coupling between the atria and mitral valve

Anterior leaflet (AL) stiffening during isovolumic contraction (IVC) may aid mitral valve closure. We tested the hypothesis that AL stiffening requires atrial depolarization. Ten sheep had radioopaque-marker arrays implanted in the left ventricle, mitral annulus, AL, and papillary muscle tips. Four-dimensional marker coordinates ( x, y, z, and t) were obtained from biplane videofluoroscopy at baseline (control, CTRL) and during basal interventricular-septal pacing (no atrial contraction, NAC; 110–117 beats/min) to generate ventricular depolarization not preceded by atrial depolarization. Circumferential and radial stiffness values, reflecting force generation in three leaflet regions (annular, belly, and free-edge), were obtained from finite-element analysis of AL displacements in response to transleaflet pressure changes during both IVC and isovolumic relaxation (IVR). In CTRL, IVC circumferential and radial stiffness was 46 ± 6% greater than IVR stiffness in all regions ( P < 0.001). In NAC, AL annular IVC stiffness decreased by 25% ( P = 0.004) in the circumferential and 31% ( P = 0.005) in the radial directions relative to CTRL, without affecting edge stiffness. Thus AL annular stiffening during IVC was abolished when atrial depolarization did not precede ventricular systole, in support of the hypothesis. The likely mechanism underlying AL annular stiffening during IVC is contraction of cardiac muscle that extends into the leaflet and requires atrial excitation. The AL edge has no cardiac muscle, and thus IVC AL edge stiffness was not affected by loss of atrial depolarization. These findings suggest one reason why heart block, atrial dysrhythmias, or ventricular pacing may be accompanied by mitral regurgitation or may worsen regurgitation when already present.

Free Vibration Analysis of Rectangular Plates with Nonuniform Lateral Elastic Edge Support

The method of superposition is utilized to obtain a solution for the free vibration of thin rectangular plates resting on non-uniform lateral elastic edge supports. The stiffness of the elastic supports may have any desired distribution along the edges, including discontinuities and local concentrations. Convergence is found to be rapid. Graphical results are plotted for square plates in order to verify that proper frequency limits are approached as the edge stiffness approach limits of zero and infinity. Results are tabulated for square and nonsquare plates in order that other researchers will have data against which they can compare their results.