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ACCELERATED TEST OF MAS 65 DEEP SOIL LOOSENING MACHINE FRAME Matache Mihai 1) , Voicu Gheorghe 2) , Cardei Petru 1) , Vladut Valentin 1) , Persu Catalin 1) , Iulian Voicea 1) 1) INMA Bucharest / Romania; 2) P.U. Bucharest / Romania

Accelerated Test of Mas 65 Deep Soil Loosening

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Testare in regim accelerat a cadrului de rezistenta a masinii MAS65

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ACCELERATED TEST OF MAS 65 DEEP SOIL LOOSENING MACHINE FRAME

ACCELERATED TEST OF MAS 65 DEEP SOIL LOOSENING MACHINE FRAME Matache Mihai1), Voicu Gheorghe2), Cardei Petru1), Vladut Valentin1), Persu Catalin1), Iulian Voicea1)1)INMA Bucharest / Romania; 2)P.U. Bucharest / Romania

The resistance frame of the MAS 65 deep soil loosening machine, also called frame, represents an essential component for its optimum functioning. The machines frame is subjected to composed mechanical strains during exploitation which could destroy its integrity. The verification of the frames resistance could be made directly in the field, through the exploitation of several hundred hectares during a working season or in laboratory conditions. Within the paper it is presented the testing method in laboratory, through simulating the field strains, based on the real stress spectrum at which the structure is subjected. After applying a rain flow type cycle counting algorithm and synthetizing a test program based on it, the frame is tested in accelerated regime within laboratory, being mounted on a testing stand fitted with hydraulic actuator. The test purpose is to experimentally determine the frames exploitation resistance in a reasonable amount of time and with minimum costs. The presented testing method could be generalized for most of agricultural equipment, representing a powerful tool in stages of designing and validation of a new product.Introduction

Testing of technical equipment before emerging on the market represents a base condition for assessing their reliability, safety in exploitation as also the obtained performances. This testing can be performed in exploitation conditions but its costly and uses large amounts of time, usually reaching the expected life of the equipment. An alternative is represented by accelerated testing. Accelerated testing can be obtained through many methods [1] by which we remind the compression of the testing period together with raising the strain level or raising the frequency and/or amplitude of strains, in function of the requirements. Thus we can obtain shorter testing periods, direct proportional with the acceleration factor [4].

IntroductionAgricultural machinery manufacturing industry is characterized by the same testing patterns in what concerns their performances as the other technical equipment. The principles used remain the same ones as in the aeronautical [5] or car manufacturing industries. Thus is very important to identify the stress spectrum at which the car is subjected. Based on this, on the used materiel properties, and after applying a cycle counting algorithm and correlated with a damage addition rule (e.g. Palmer-Miner), one could determine the expected life of the structure. Also it could be realized an accelerated testing program [7,8] at which the structure to be subjected in laboratory conditions for assuring a minimum life expectancy, for example a minimum number of seasons in which the structure could be exploited.

IntroductionThe main strains of agricultural machines are of mechanical type and they have a direct effect on their resistance structures, also called frames. In this paper we refer to the deep soil loosening machine MAS 65, whose frame is highly stressed in exploitation. Because of this reason there could appear permanent deformations or fissures which could affect its structural integrity and the working capacity. For avoiding such situations, the frame has to be tested in the field and/or in laboratory conditions. In order to obtain the results which evaluate the frame from the resistance in exploitation point of view, we chose to identify the stress spectrum in the field, based on which to synthetize an accelerated testing program in laboratory conditions. After that the frame was subjected to this testing program, simulating the usage during one exploitation season.

Method

In order to obtain the most stressed points in exploitation of the MAS 65 resistance frame, first we performed a finite element analysis, in static regime on the machines structural model

Deep soil loosening machine MAS The field of equivalent stress (Von Mises) into the structure, in PaMethod

Real stress spectrum obtained after in field experiments, for the working element of the MAS 65 machineMethodMethodMethodMethodMethodMethod

Accelerated testing stand for the resistance frame of MAS 65 machineResults and discussions

After field experiments we obtained the diagrams presented in figure 3. The total observed time obtained by concatenation was ttot=110 seconds. Applying the rainflow counting algorithm to the obtained signal, with a gate factor of 10%, it resulted a total number of 498 stress cycles

Fig. 6. Rainflow cycle counting algorithm results Results and discussionsThe obtained cycles were divided by their range stress in 10 bin of equal width, with a common mean stress.

Fig. 7. Number of cycles per testing bins Results and discussionsNo of binNo of cyclesai (MPa)i (Hz)ti (sec)Ti (sec)102.846700024238.540114.9493.4328.3135314.23358.9611.715.9141219.92696.402.651.875525.62034.981.101.006431.31374.070.880.987037.00710008042.70050009048.393900010154.08732.360.220.42Results of the proposed testing algorithm Results and discussions

Synthetized test program Results and discussionsTaking into account that we estimated a surface of 150 ha worked/season, with a medium working speed of 2 km/h and a medium working width of 1.5 m, the total number of stress cycles estimated per season was of 8964000. This fact implied the repetition of the accelerated testing program by 18000 times. The total amount of accelerated testing time was of 192.5 hours compared with the 500 hours of conventional testing. After completion of the tests we didnt find any fissures, ruptures or deformations in the frame of MAS 65 machine.Results and discussionsThe tests acceleration method used was that of weighted raising the test frequencies, according to equation 6. Performing the ratio between the initial total time of the concatenated signal and the total time of the synthetized signal, we got an acceleration factor AF=2.857, which is very closed to the value of 3 obtained by other researchers for agricultural machinery and tractors . In this way a working season could be simulated in 8 days of testing, the costs for this activity being much smaller than that of conventional testing. Also the time in which we get the results allows for assessment of machines performances much quicker than in the conventional manner. Conclusions

As we can observe the rainflow counting algorithm does not contain any information referring to frequency of stress cycles. In the paper we proposed a calculus algorithm for the testing frequencies which takes into account the stress range, so that the testing frequency to be invers proportional with the stress range. This permits a correct frequency response of the testing stand and also a good acceleration factor.

Conclusions

Agricultural machines for which we estimate a high degree of mechanical stress during exploitation, the determination of life expectancy and of reliability indicators in normal conditions presumes a large amount of testing time. Because of that one can choose accelerated testing methods. Those are tests performed at higher or quicker stress levels, compared with the normal stress level, in order to intensify the failure mechanisms of the equipment, and as an economical result the shortening of the testing period and the reducing of testing costs, in the conditions of keeping the same failure mechanisms. Within the accelerated tests we accept the hypothesis that the life expectancy of the product decreases proportional with the intensifying of the stress. Conclusions

Tests in laboratory conditions will not describe totally the real situation from the field, because there are constraints regarding the geometry of the testing stand, limitations of the testing devices as also the missing of some field factors (for example speeds, accelerations, moving elements). Still this type of testing remains a valuable tool for engineers because of the possibilities to obtain in a very short amount of time informations regarding the structural integrity of the equipment, its reliability, failure mechanisms, etc. Also the acceleration method and the value of the acceleration factor have to respect the engineers good practice guides.References

[1]. Alex Porter (2006). Accelerated testing and Validation[2]. Buzdugan Gh. (1980). Strength of Materials, Technical Publishing House, Bucharest[3]. Cardei P. and others (2012). Structural analysis and new materials focused on mechanics, mechatronics, maintenance and operation of technical equipment for agriculture and food industry, Terra Nova Publishing House, Iasi[4]. C.M. Sonsino (2006). Fatigue Testing Under Variable Amplitude Loading, International Journal of Fatigue volume 29 10801089.[5]. Gassner E. (1939). Festigkeitsversuche mit wiederholter Beanspruchung im Flugzeugbau (Strength tests under repeated loading for aeronautical engineering). Luftwissen;6:614.[6]. Michele Mattetti, Giovanni Molari, Enrico Sedoni (2012). Methodology for the realisation of accelerated structural tests on tractors, Biosystems Engineering, volum 113, pp 266271. [7]. Vldu V., Biri S., Bungescu S., Dima I., Punescu D.(2004). Computer-aided test of the disk harrow GD 3.2 in simulated and accelerated regime on the hydropulse installation and the stress states analysis, ANALS OF THE FACULTY OF ENGINEERING HUNEDOARA, Tome II, Fascicule 1, P.U. of Timioara, pp. 25-30, ISSN 1584-2665, Editura MIRTON, Timioara - Romnia;[8]. Vldu V., Gngu V., Pirn I., Bjenaru S., Biri S., Bungescu S.(2007). Complex tests of the resistance structures in simulated and accelerated regime on hydropulse installation, PROCEEDINGS OF THE 35 INTERNATIONAL SYMPOSIUM ON AGRICULTURAL ENGINEERING "Actual Tasks on Agricultural Engineering", pp 393-404, ISSN 1333-2651, Opatija - Croaia[9]. Wirsching, P. H., Mohsen Shehata, A.(1977).Fatigue Under Wide Band Random Stresses Using the Rain-Flow Method. Journal of Engineering Materials and Technology.

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