Software_System_Architecture_and_Design_Features.pdf (1311946Bytes)
I helped a friend in coding a data logging software for a custom built fatigue testing machine and would like to share.
1.1 Introduction
When material parts fail statically, they usually developed a very large deflection because the stress exceeds the yield strength of the material. This can be easily identified and the machine part replace before failure. However, fatigue failures give no such indication; the machine component will just fail suddenly, and dangerously. Fatigue failures occurs due to dynamic loading which produce repeated or fluctuating stresses within the material over a period of time. Fatigue testing machines allow machine component test samples to be tested under dynamic loading condition so that proper maintenance procedure can be put in place by maintenance engineers to prevent abrupt failure during service. With the appropriate data logging system installed on a fatigue testing machines, as entailed in this project, specimen test results can be accurately, documented, stored and analyzed.
1.2 Rationale
The fatigue testing machine is already built but it has no data logging system. By installing a computerize data logging system specimens test results can be effectively documented, store and analyzed. Standardization of the machine can then be achieve so that bachelor and graduate student can be given the opportunity to performed laboratory tests and research on standard test samples as well as other samples up to one inch.
1.3 Objectives
1.To design and installed a computerized data logging system on a Custom built fatigue testing machine located in the Strength Laboratory.
2. To test the accuracy of the Custom built fatigue testing machine by performing standard specimen tests with steel, aluminum and brass samples.
1.4 Project Scope
Through extensive research and analysis a cost effective and reliable computerized data logging system will be design and constructed for the already built fatigue testing machine located in the Strength Laboratory. This system will be installed and standard specimen tests conducted using steel (RF1010) samples, Aluminum (RF1020) samples and brass (RF 1030) samples. Similar sample tests will be conducted on the newly commission computerized rotating fatigue testing machine (SM1090) located in the Strength Laboratory, the results will be compared and the accuracy of the data logging system and the Custom built fatigue machine will be validated.
1.5 Results Discussion
Based on the results obtained from the test samples of Aluminum and Brass it can be presume that for the Custom Built fatigue testing machine, Aluminum - the time to failure varied 89.66 s from the mean time of 64.4 s, “Neck Diameter” vary 0.00013 mm from the mean value of 4.06 mm, Total count Vary 51, 462.3 from the mean value of 1,302.6 and Load vary 0.0005 N from the mean load of 71.12 N. For Brass - the time to failure varied 103,049.3 s (28.6 hrs.) from the mean time 1,278.4 s (0.36 hrs.), “Neck Diameter” vary 0.00013 mm from the mean diameter of 4.06 mm, Total count Vary 40,627,022.3 from the mean Load of 25,528.6.
From the Result obtain for the SM1090 fatigue testing machine, Aluminum - time to failure varied 149.33 s from the mean time of 69.33 s, “Neck Diameter” vary 0.00015 mm from the mean Diameter of 4.06 mm, Total count Vary 51,977.34 from the mean count of 1,333.33 and Load vary 0.084 N from the mean Load of 71.57 N. For Brass - time to failure varied 240,897.34 s from a mean time of 961.33 s, “Neck Diameter” vary 0.00015 mm from the mean value of 4.06 mm, Total count Vary 48,101,552.33 from the mean count of 18,473.33 and Load vary 1.33 N from the mean load of 72.6 N.
The variance from the mean values obtain from Custom Built fatigue testing machines as compare to that obtain from the SM1090 fatigue testing machine is lower in value. This indicate that there is smaller variation within the data obtain from the Custom Built fatigue testing and also account for the accuracy of the machine when compared. Smaller variation in the data obtain for aluminum and brass samples when tested at the same Load and “Neck Diameter” as shown in Table 9 is also a strong indication of the accuracy of the machine. Moreover, observation on the test samples after failure indicates that all the test samples fail along the same area.
The results shows that both machines are comparable, and that the Custom Built fatigue testing may even have a higher degree of accuracy base the lower degree of variation of its values from the mean. Analyzing the difference in variance obtain from the test samples from both, shows that the resulting fluctuation is quite small in relation to the sample size and within a reasonable range.
The Steel sample was tested at increasing load. This was done to test the capacity of the Load cell. However beyond the equivalent load of 458.18 N, the mild steel test sample experience severe bending, and further testing had to be abandoned. Such a load is impossible to be applied to SM1090 which can only handle a maximum load of 73 N. Therefore, the load cell is capable of testing steel, brass and aluminum samples of “neck diameter” 4.04 -4.07 mm. The graphs obtained from the tests conducted on both machines shows the fatigue loading conditions at each point on the test specimen base on the Data Capture Rate. The Test samples or specimen experience a series of momentarily stress variation due to the slight changes in its bending moment throughout it cyclical rotational speed. In Addition, eight and six hour’s tests were done on a steel sample at zero loading to test the durability of the RR- 2015 Data Capture Unit as well as an attempt to max out as many digits on the LCD as possible. The LCD can display up to 12 digits (1012) but it was only possible test it up to six digits (106).
Conclusion
From the analysis done on the test results, it can be concluded that the RR- Data Capture Unit installed on the Custom Built Fatigue Testing Machine is comparable and is as accurate as the Data Acquisition System found on the SM1090 Fatigue Testing Machines. The only limiting factor for SM1090 was it small sample size, and this was because the machine developed mechanical problems during sample testing. Presently, it is out of service awaiting mechanical parts. From the 6 hours and 9 hours test completed on the Custom Built Fatigue Testing Machine, demonstrate that the RR – 2015 Data Capture Unit is Robust, durable and have the ability to test specimen up to 1inch. It can be presume that the main objectives of this project were successfully achieved. A computerized data capture unit was designed, build, installed and tested on the Custom Built Fatigue Testing Machine and result obtain from standard test done on Aluminum and Brass sample indicate that the machine is standardize in relation to SM1090 Fatigue Testing Machine.
