An Analysis model for the design and control of tractor protective cabs

The purpose of this study is to present an analysis model to control and to support the design of tractor protective cabs. The protective cabs are used to protect drivers of tractors by minimizing the likelihood of driver injury resulting from accidental overturning during normal operations. The protective cabs shall be to production specifications and shall be fitted to the appropriate tractor model chassis. These cabs should be designed to meet safety regulations for rolling over protective and falling object protective. These safety requirements are important for driver and therefore protective cabs are tested by international and national standard test procedures as ISO 3463, ISO 5700 and TSE 3412. In fact, there are four methods to examine the safety of driver by using a protective cab when tractor overturns : 1) Real Overturning Test Method : A tractor having protective cab is overturned in a slope. 2) Dynamic Test Method : The strength of the protective structure is tested by simulating such loads as are imposed on the cab when the tractor overturns either to the rear or to the side. It includes the three impact tests from the rear, the front and the side; the two crushing tests at the rear and the front. During impact tests the application of a dynamic load produced by a block with a mass of 2000 kg acting as a pendulum. During crushing tests the application of a vertical load through a beam placed laterally across the uppermost members of the protective structure. 3) Static Test Method : The strength of the protective structure is tested by applying static loads to simulate actual loads which may be imposed on the cab when the tractor overturns either to the rear or to the side. It includes the three horizontal loading tests and the two crushing tests. During horizontal loading test, a horizontal load is applied the rear, the front and the side of the structure. The crushing tests are the same as those in dynamic test method. 4) Prediction Approach : To apply the three test methods that have been briefly explained above, one needs manufactured cabs as well as a lot of time and money. The most important decisions concerning the future cab are made in the early stages of design, when little or no hardware is available for testing and when considerable XUlAccording to standard static test method, five sequence loadings are applied to the protective cab. These are : 1) A rear corner of the cab is loaded. 2) The cab is then crushed at the rear by a static load. 3) A loading on the side of cab is applied. 4) A vertically crushing at the front with a static load. 5) Finally a load at the front on the corner diagonally opposite that (1) is applied. These loading sequences have been applied in the same order in the KABAN program. In the first, the third and the fifth loading stages, when energy reaches to a certain limit which is calculated according to tractor mass, loading procedure is stopped and unloading procedure starts. In the second and the fourth crushing stages when the load reaches to a certain limit loading ends and unloading starts. At the end of the every stage any part of cab must not intrude into zone of driver's working space. If it intrudes, the program is interrupted. This shows that the cab is unsafe. The developed KABAN program was applied to 2 real different cabs and the obtained outputs have been compared and discussed with those obtained from tests. The result is very encouraging and it can be stated that the KABAN program will be a powerful tool to control and to support the design of protective cab. The first part of KABAN program gives possibility to search the effects of different kinds of soils, the angles of slopes, the treads of tractors, the heights of tractor center of gravity, the widths and the heights of cabs on the rolling over. The second part of KABAN program controls the strength of protective cab structure in a very similar way to standard static test method and gives quite compatible results. It has been shown that it is possible to reduce material weight used in design as far as 20 percent providing some protective requirements. xvmtime and money would be necessary to evaluate the various design alternatives to produce an optimum cab design. Although there are some works to calculate protective cab, there is no generally accepted analytical procedure to substitute the expensive laboratory tests yet. In this study, a comprehensive mathematical model is developed to control the safety requirements of manufactured protective cabs as well as to support their design in the early stages of design. Based on this model a computer program in FORTRAN- 77 called KABAN has been prepared. The developed analysis model for protective cabs contains two main parts. In the first part, it has been searched how a tractor equipped with a cab rolls over and over after accidental overturning on slopes and which geometric dimensions of protective cab can stop to roll over. In the second part, the carrying structure of protective cab has been analyzed by using finite element method, so that the cab could have sufficient strength for rolling over protective and falling object protective. On slopes tractors overturn 85 percent on their sides by accident when they loss their stability. During this process the potential energy of tractor mass turns into kinetic energy. The tractor overturning and strikes with a rotational velocity on the ground first on its back tire then at the corner of cab which sinks into ground. Some parts of kinetic energy is absorbed by soil. In the literature the sinkage of cab corner into soil is assumed as 10 cm, 20 cm and 30 cm. But in this work the sinkage and the absorbed energy by soil are calculated by using Bekker's pressure-sinkage relationship obtained from plate penetration tests as (1) where p is the pressure on the ground, t is the sinkage, b is the smaller dimension on the loading area, n is the exponent of deformation, kcand k^are cohesive and frictional module of deformation respectively. After the cab corner sinks into soil, if the rest of kinetic energy is still sufficient or in other words the rotational velocity of tractor is not zero, the tractor rolls over and over. The developed analysis model is based on the equations of energy transformation and gives a possibility to predict the optimum cab dimensions related soil conditions, slopes and tractor dimensions. xivAccording to standard static test method, five sequence loadings are applied to the protective cab. These are : 1) A rear corner of the cab is loaded. 2) The cab is then crushed at the rear by a static load. 3) A loading on the side of cab is applied. 4) A vertically crushing at the front with a static load. 5) Finally a load at the front on the corner diagonally opposite that (1) is applied. These loading sequences have been applied in the same order in the KABAN program. In the first, the third and the fifth loading stages, when energy reaches to a certain limit which is calculated according to tractor mass, loading procedure is stopped and unloading procedure starts. In the second and the fourth crushing stages when the load reaches to a certain limit loading ends and unloading starts. At the end of the every stage any part of cab must not intrude into zone of driver's working space. If it intrudes, the program is interrupted. This shows that the cab is unsafe. The developed KABAN program was applied to 2 real different cabs and the obtained outputs have been compared and discussed with those obtained from tests. The result is very encouraging and it can be stated that the KABAN program will be a powerful tool to control and to support the design of protective cab. The first part of KABAN program gives possibility to search the effects of different kinds of soils, the angles of slopes, the treads of tractors, the heights of tractor center of gravity, the widths and the heights of cabs on the rolling over. The second part of KABAN program controls the strength of protective cab structure in a very similar way to standard static test method and gives quite compatible results. It has been shown that it is possible to reduce material weight used in design as far as 20 percent providing some protective requirements. xvmtime and money would be necessary to evaluate the various design alternatives to produce an optimum cab design. Although there are some works to calculate protective cab, there is no generally accepted analytical procedure to substitute the expensive laboratory tests yet. In this study, a comprehensive mathematical model is developed to control the safety requirements of manufactured protective cabs as well as to support their design in the early stages of design. Based on this model a computer program in FORTRAN- 77 called KABAN has been prepared. The developed analysis model for protective cabs contains two main parts. In the first part, it has been searched how a tractor equipped with a cab rolls over and over after accidental overturning on slopes and which geometric dimensions of protective cab can stop to roll over. In the second part, the carrying structure of protective cab has been analyzed by using finite element method, so that the cab could have sufficient strength for rolling over protective and falling object protective. On slopes tractors overturn 85 percent on their sides by accident when they loss their stability. During this process the potential energy of tractor mass turns into kinetic energy. The tractor overturning and strikes with a rotational velocity on the ground first on its back tire then at the corner of cab which sinks into ground. Some parts of kinetic energy is absorbed by soil. In the literature the sinkage of cab corner into soil is assumed as 10 cm, 20 cm and 30 cm. But in this work the sinkage and the absorbed energy by soil are calculated by using Bekker's pressure-sinkage relationship obtained from plate penetration tests as (1) where p is the pressure on the ground, t is the sinkage, b is the smaller dimension on the loading area, n is the exponent of deformation, kcand k^are cohesive and frictional module of deformation respectively. After the cab corner sinks into soil, if the rest of kinetic energy is still sufficient or in other words the rotational velocity of tractor is not zero, the tractor rolls over and over. The developed analysis model is based on the equations of energy transformation and gives a possibility to predict the optimum cab dimensions related soil conditions, slopes and tractor dimensions. xivAccording to standard static test method, five sequence loadings are applied to the protective cab. These are : 1) A rear corner of the cab is loaded. 2) The cab is then crushed at the rear by a static load. 3) A loading on the side of cab is applied. 4) A vertically crushing at the front with a static load. 5) Finally a load at the front on the corner diagonally opposite that (1) is applied. These loading sequences have been applied in the same order in the KABAN program. In the first, the third and the fifth loading stages, when energy reaches to a certain limit which is calculated according to tractor mass, loading procedure is stopped and unloading procedure starts. In the second and the fourth crushing stages when the load reaches to a certain limit loading ends and unloading starts. At the end of the every stage any part of cab must not intrude into zone of driver's working space. If it intrudes, the program is interrupted. This shows that the cab is unsafe. The developed KABAN program was applied to 2 real different cabs and the obtained outputs have been compared and discussed with those obtained from tests. The result is very encouraging and it can be stated that the KABAN program will be a powerful tool to control and to support the design of protective cab. The first part of KABAN program gives possibility to search the effects of different kinds of soils, the angles of slopes, the treads of tractors, the heights of tractor center of gravity, the widths and the heights of cabs on the rolling over. The second part of KABAN program controls the strength of protective cab structure in a very similar way to standard static test method and gives quite compatible results. It has been shown that it is possible to reduce material weight used in design as far as 20 percent providing some protective requirements. xvm