Cyclic Mechanical Fatigue Lifetime of Bi0.5Na0.5TiO3-Based Eco-Piezoceramics

The mechanical strength and cyclic fatigue behavior of PIC700 commercial eco-piezoceramic disks are investigated under biaxial loading on unpoled and poled samples. The bending strength of unpoled samples was higher than those of poled ones. Fatigue tests were conducted under a load ratio of 10 at a frequency of 20 Hz with a sinusoidal waveform. The curve fitting for the S-N fatigue diagram is used to predict the lifetime of these eco-piezoceramics and describe their fatigue behavior. It was also found that the unpoled samples exhibited higher fatigue resistance than the poled ones. The fatigue limit of maximum load for ten million cycles of unpoled and poled samples was estimated to be 160 and 135 MPa, respectively. The detailed observations of the fatigue fracture surfaces by scanning electron microscopy (SEM) indicated that a wavy surface with a mixture of transgranular and intergranular fractures occurred preferentially in the case of the poled material. On the other hand, transgranular fractures seem to be predominant in the unpoled samples. It appears that the poling process causes the change in failure characteristics due to domain orientation that leaves an anisotropic stress field in the material. The poled ceramics possess a local stress concentration created by the orientation under the electric poling field of the 90° ferroelectric–ferroelastic domains. Under this local stress concentration, a microstructural degeneration is induced by domain switching under the cyclic load that accelerates crack growth, thereby reducing fatigue lifetime.

Improving fatigue performance of surface-damaged Ti-6Al-4V alloy via ultrasonic surface rolling process

Surface damages caused by markings, like laser marking and mechanical marking are detrimental to the fatigue performance of the components. To improve the fatigue performance of laser marked or mechanical marked Ti-6Al-4V alloy, ultrasonic surface rolling process (USRP) was performed on Ti-6Al-4V alloy prior to marking. The results showed that laser marking induced a porous and loose oxidized layer which severely decreased the fatigue performance of the substrate. And the mechanical marking slightly decreased the fatigue performance of the substrate due to the local stress concentration at the bottom of the pits. After USRP pretreatment, the detrimental effect of laser marking on the fatigue performance of the substrate was eliminated while the fatigue performance of mechanical marking sample was significantly improved by a factor of 3. That was because the USRP-induced residual compressive stress suppressed the crack early propagation. Key words: Titanium alloy; Fatigue; Ultrasonic surface rolling process; Surface damage; Residual compressive stress; Laser marking, Mechanical marking

Effect of Coal Loading Conditions on Structural Characteristics of LFTS

Indonesia is a main country supplying coal in the Asia-Pacific region, it is important to ensure a stable coal supply to Japan. Because the topography of the seabed near East Kalimantan Island, Indonesia’s main coal production area, is shallow, it is difficult for bulk carriers to reach the coast. Therefore, Large-Scale Floating Coal Transshipment Station (LFTS) was proposed, which will be used as a relay base between coal-barging barges from land and bulk carriers offshore. Installing an LFTS offshore from East Kalimantan is expected to improve coal transport productivity. LFTS can store coal equivalent to five times the capacity of one bulk carrier (total 500,000T), and can accommodate 2 bulk carriers at the same time during offloading. The scale of LFTS is 590m × 160m. The LFTS has a flat spread and the elastic behavior becomes the dominant Structure. The upper part of the LFTS is different rigidity partly because the partition wall to be loaded by dividing the coal into each quality is provided. Loaded coal not only changes the draft of the LFTS but also greatly deforms the LFTS and is expected to cause local stress concentration on the structural members. Therefore, this paper investigates wave response characteristics and stress characteristics with the coal loading of the LFTS, and then evaluation of structural strength by limit state design method. In this study, linear potential theory and the finite element method (FEM) were used to analyze the static hydroelastic motion under various coal loading condition and wave response of LFTS. And, to grasp the local stress concentration occurring inside the LFTS by using the response results, a detailed model modeling a complicated internal structure was prepared. Zooming analysis which is a method of giving the deformation result by the whole model of LFTS as forced displacement to the local detailed model was carried out. As a result, depending on the coal loading condition and wave conditions, it became clear that LFTS will be in a tough situation.

Determination of DC06+ZE Sheet Crack Cause

The present work deals with determination of the cause of crack occurring in a part of car body manufactured from deep-drawing sheet. UHR-SEM, EDS, EBSD and measurement of microhardness were used for evaluation of the structure, local deformation and crack formation mechanism. A material analysis discovered foreign particles in the material. These particles were identified as MgAl2O4 with BCC lattice. The occurrence of these hard particles led to local stress concentration, decrease in mechanical strength and sheet breach due to tensile stress during deformation.

Reduction of Local Stress Concentration on Nanosheet in Layered Nanoparticles with Water Molecules

The local stress concentration on 2D nanosheets is investigated for saponite layered nanoparticles by means of X-ray diffraction (XRD) and positronium (Ps) annihilation spectroscopy. XRD experiments indicated that the layered structure for the mechanochemically milled sample is maintained in the presence of H 2 O molecules. Ps annihilation studies of self-assembly revealed that the 2D nanosheets are well in-plane ordered after uniaxial pressure compaction without H 2 O molecules due to the efficient propagation of stress concentration. The present results of both XRD and Ps lifetime spectroscopy clearly demonstrates that the stress concentration on the 2D nanosheets can be reduced in the presence of H 2 O molecules.