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How One Grad Student deals with STRESS

While most of us are trying to reduce the level of stress in our lives, Pete McKeighan, a graduate student in Mechanical Engineering, spends his time in ME's Materials Lab stressing things to the max! One of the research areas studied by the Materials Lab, directed by Professor Ben Hillberry, involves testing a materials property called KdIcu which characterizes the fracture behavior of materials. In very simple terms, Pete runs an experiment that sinusoidally beats on a metallic specimen until it "grows a crack suitable for fracture". The applied loading is produced by a MTS servo-hydraulic test machine which applies loads from -20,000 to 20,000 lbs. Pete has developed a nifty software system that handles data acquisition, controls the experiment and performs data analysis in a fashion that simplifies the testing procedure and gives the user critical feedback during the experiment. The software, named EZ KdIcu, was developed over a ten month period and consists of about 4000 lines of "C" code. It makes use of the Suntool, Sunwindow, Pixrect, and CRC plotting libraries and floating point optimization. Pete took advantage of the Sun's graphics capabilities to make the software easy to use with mouse picked menu options and to give the user plenty of visual feedback with immediate data plotting. The figure below shows a typical Sun console screen during execution of the program.

               figure in newsletter showing screen

The software was developed for a specific combination of hardware, consisting of the Materials Lab's MTS servo-hydraulic test machine, a Sun 3/180 standalone workstation (matlab) and Burr-Brown data conversion boards (A/D and D/A). The two 12 bit 8 channel Burr-Brown (Tucson, AZ) data acquisition boards are installed in the VME bus of the Sun. These boards each have their own internal on-board memories (16K words for the D/A and 32K words for the A/D) and triggers. Their conversion rates or sampling periods are extremely fast. For the A/D it varies between 3 and 256 microseconds between points with a step size of 1 microsecond. The D/A internal trigger can convert data every 1.5 to 127.5 microseconds with a step size of 500 nsec. The data acquisition boards are some of the first to be used with Suns at Purdue and are controlled by a special psuedo device driver (using "mmap", a Sun UNIX system call) written by Charles Mok, a Purdue EE student.

Some advantages of the system include:

• Complete turn-key begin to end test software
• Adaptive feedback control during fatigue cycling
• Achieves real-time control in a UNIX environment
• Uses multi-tasking capability of UNIX to run processes in parallel
• Menu-driven, user-friendly, mouse picked user interfaces
• Provides data plotting "on-the-fly"
• A/D & D/A input/output rates independent of Sun CPU (due to Burr-Brown on-board memories and triggers)
• Extremely fast A/D & D/A
• Complete post-fracture analysis of results
• Harnesses speed and computational capability of the Sun

In the past, software systems similar to EZ KdIcu have been used in the Materials lab (as well as commercially) with PC's. This application utilizes key advantages inherent in the Sun UNIX environment. It's computational speed and graphical output surpasses that typically found with PC's. EZ KdIcu represents the first generation of real-time control software used in the Materials lab that has been achieved with UNIX. As UNIX becomes increasingly popular, we will be seeing more of this type of application.

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