The rise of NDE In the early 1970s the discipline of fracture mechanics emerged This enabled one to predict whether a crack of a certain size would fail under a specific load if certain properties were known Laws were developed to predict the rate of growth of cracks (fatigue) under cyclic loading Components with KNOWN defects could still be used if it could be established that they were not of a critical, failure producing size
Ultrasonic testing Ultrasonic testing uses high-frequency sound waves that are directed into a material to locate changes in material properties The most common approach is pulse-echo where sound is introduced to the object and reflections (echoes) are returned to a receiver from internal imperfections The reflected wave signal is transformed into an electrical signal by a transducer
Enabling a learning environment Complex theory can be engaged with through practical application of ideas - labs Cost of a traditional lab prohibitive –Ultrasonic probes –Unique flaw arrangements A virtual environment can be created through the simulation of a process
Ultrasonic testing in practice
Creating the virtual environment 33 crew rescued off Eastern Cape coast More than 30 crew members were forced to abandon the 299-metre bulk carrier Alexandros T in life-rafts when it started sinking some 300 nautical miles off Port Alfred on the Eastern Cape Coast. Salvage vessel Smit Amandla, passing ships and the National Sea Rescue Institute (NSRI) plucked the 33 sailors to safety late last night in five- metre swells and 45 knot winds. The Alexandros T was sailing from Brazil to China, when it broke up, took on water and sank. Hellenberg said the reason for the vessel sinking had not yet been established.
Sinking of Alexandros T shows a design rethink is necessary These Capesize vessels - three rugby fields in length - are very susceptible to the power of the sea. With a heavy swell on the quarter, they flex significantly, a phenomenon factored in by their designers. Nevertheless, while the wing tanks and the ore cargo impart some rigidity to the lower part of the hull, stresses on the rest of the ribs and side plating can be severe. Corrosion around the wing tanks can be difficult to detect and treat, and subsequent weaknesses in the plating will inevitably cause cracks that are exploited by heavy seas or by the iron ore slurry created in a flooded hold.
Developing a three-part virtual laboratory Use an ultrasonic probe to locate the flaws Process the data collected with an oscilloscope Write a assessment of the flaws as the ship engineer
Flaw location Moving an ultrasonic probe across the hull of a ship An accurate representation of what the output on a real oscilloscope would have been Students have their own randomly generated flaws (within set parameters) to detect
Finding the flaws
Analysing the data Each spreadsheet is personalised Depth and orientation of the flaws are determined Calculations straightforward Interpretation of the results is not obvious
Interpreting the results Students take the role of the ships engineer Justify their assessment as to whether the ship can continue in service Alexandros T used frame the activity Need to draw on their tacit knowledge of engineering draw from other courses
The value of ET to me Using technology in this way allowed me to create a learning environment that is difficult to achieve in a traditional laboratory setting It is possible to introduce complex practical aspects into a course that can help build on the theoretical content students have traditionally received