Volume 53, Issue 6

This study addresses the determination of the fatigue life and its failure locations of the vehicle cylindrical LPG fuel tanks using both experimental and finite element analysis (FEA) methods. The experimental investigations performed as an accelerated fatigue tests are carried out using a hydraulics test unit in which the cylinders are internally pressurized by hydraulic oil. The LPG cylinders are subjected to repeated cyclic pressure varying from zero to service pressure of the tank. The FEA modeling of these tanks are developed in three dimensional (3D) using non-uniform geometrical parameters and nonlinear material properties. These models are also subjected to zero-based high cycle fatigue pressure load considering the stress life approach. The FEA modeling process is also simulated in non-homogeneous material conditions. Therefore, the fatigue life performance and failure location of the cylindrical LPG fuel tanks are predicted and compared to the experimental results.

This work presents a method to improve visualisation of metallographic structures in titanium containing alloys. After conventional selective chemical etching with Kroll’s reagent, the surface of the sample specimen is manually dyed with a phtalocyanine based lacquer. The results are highly detailed and sharp coloured images when investigated with Optical Microscopy, providing much more information compared to the grey shaded, etching only approach.

Accredited metallography laboratories are required to estimate the uncertainty of the result of every test carried out. This presents a particular challenge in evaluating the cleanliness of a metal as usually a particle distribution – log-normal at best and represented by a tiny sample size – is truncated and split into discrete classes. Therefore, neither indirect (top-down) nor direct (bottom-up) methods succeed in estimating the uncertainty of cleanliness evaluations. For these reasons, such evaluations should be viewed through a process surveillance lens, particularly when discussing results or setting acceptance thresholds.

All of us have seen it: a raindrop running down the windowpane. It stops at a certain point, is met by a second raindrop and the two join up before continuing to run down the pane. Very small irregularities or dirt on the windowpane appear to stop the course of the raindrops. If the surface was entirely smooth and chemically clean, the raindrops would be able to flow unhindered. Surface defects such as small bumps and dimples as well as chemical contaminants stop the liquid drops. These are everyday phenomena everyone knows and can observe with the naked eye.