baja sae brazil structural report

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Bajara Team Report

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Introduo (Quem; O que; Como, Por que; Quando, Onde; Quanto)

Bajara Team Report

IntroductionThe Bajara Team from the Federal University of the West of Par, located in Santarm - Par - Brazil, carried out simulations of several situations that could occur, using Ansys software, before the construction of its off - road vehicle. The general purpose is to participate in the 22nd SAE Brazil Baja Competition that occured in the city of So Jos dos Campos - SP - Brazil. The vehicle's roll cage is the object of study.

The roll cage is the sustaining structure of all vehicle subsystems. It is also responsible for protecting the pilot's life on specific conditions of impact. A structure for this purpose shall be deformed and ruptured before transferring the energy of any loads suffered to the subsystems or to the pilot.

Objectives Simulate the response of vehicle's roll cage in the following situations: free body modal analysis; rigid body modal analysis; roll cage's behavior when it's subjected to frontal and lateral collisions; roll cage's behavior in rollovers. All of this is necessary to the identification of sharp or fatigue frequencies at welding points when the vehicle is traveling on uneven ground or accidents and it is important do determinate if pilots life is protected.

VocabularyThe following vocabulary will be adopted :Rear Roll Hoop (RRH) ;Roll Hoop Overhead members (RHO);Lower Frame Side members (LFS) ;Front Bracing members (FBM) ;Lateral Cross Member (LC) or (FLC);

Figure 1: Roll cage tubes.

Modelo de anlise

Figure 2: Chassis model designed in a computer aided design program (CAD).Figure 3:Real model picture.

Figure 4: Details of the geometry used in ANSYSFigure 5 : Details of the other masses (pilot, engine and steering system) that are part of the structure.

Figura 6: about the mesh applied in the geometry.

Figure 7: units of measurement adopted..

O material do chassi: ao SAE 1020Table1:steel pipes material.

Anlise moda de corpo livre

Frequency(Hz) As the first six frequencies are zero, Ansys had no trouble recognizing a geometry.

Figure 8: The first six frequencies are zero in free body modal analysis.Table 2 :the first Twelve natural frequencies of the structure.

Rigid body modal analysis

Vista geral

Figure 9: six first modes of vibrating with the structure attached to the suspension system.Table 3: Six first frequencies of rigid body.

52,094 HzTorsional frequency capable of causing fatigue to RHO and LC joints.

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71,743 Hz

Torsional frequency capable of causing fatigue to LFS and USM joints.

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76,859Hz

Torsional frequency capable of causing fatigue to LFS and USM joints and with greater intensity and involving more parts of the structure.

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90,001Hz

Torsional frequency capable of causing fatigue to RHO joints causing fatigue to it's welds. Other regions of the roll cage also dissipate energy .Click on the image to animate

132,4Hz

Torsional frequency capable of causing fatigue to the joints at the rear of the frame where the engine and fuel tank are fixed. The energy is also dissipated through RHO.

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146,6Hz

Torsional frequency capable of causing fatigue to RHO joints.

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Static structural analysis

This is true for rollover and collision analysis.Figure 10: details of static structural analysis.

RolloverThe forces applied to the roll cage were calculated with basis on vehicle's mass and adr59 from the Australian Protocol. The forces used are: front load; side load; vertical load. All these applied to LC upper front. The choice of this element is due to this being the least resistant part of the structure in a possible rollover. The hypothesis adopted for the value of the forces is based on the speed developed by the vehicle in the competion conditions. It is possible to deduce the height of jump force of impact with the groundwhen the vehicle passes through a ramp in its maximum speed.

Front load5880N

Details of forceRelation time (s) Vs Force (N)

The previous figure and the animation above shows the deflections. It is observed in the structure that the maximum deflection point is in the LC, exact location of application of the rollover frontal force. It is also possible to notice that the deformation is greater in RHO tubes. The deformations presented are within the safety and comfort limits of 150 mm from SAE and 100 mm from adr59. The largest deflections are observed in the FBM.

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4440N

Details of forceRelation time (s) Vs Force (N)

The previous figure shows deflections contours. The limits of deflections are within those recommended by the SAE (150 mm) and adr59 (100 mm). The amplitude of such displacements begins to cause the application of undesired forces to the pilot, but is not, however, dangerous.

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11760N

Details of forceRelation time (s) Vs Force (N)

The figure shows the deflections contour. The points of greatest deflection are LC and RHO. The range of displacement shows comfort and absence of danger to the pilot.

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Collision ForcesThe collision forces presented in the model were estimated based on the linear momentum variation rate. The mass used was the vehicles mass with all its subsystems which is approximately 250 kg. The speed used was 60 km / h, the maximum speed in which the effects of air resistance are negligible.

249000N249000N

Details of forceRelation time (s) Vs Force (N)

This force was estimated when the vehicle is in a straight line and with maximum speed (60 km / h). The figure shows the deflections contour. The deflection is larger in the Front Bracing Members (FBM) and propagates to the back of the structure decreasing in amplitude as it progresses. Its maximum value is within the limits of safety and comfort(SAE and adr59).

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249000N

Details of forceRelation time (s) Vs Force (N)

The previous figure and the animation above shows the deflections contour. Maximum deflections show that the safety limit is not exceeded, but much of the impact energy will be transmitted to the pilot.

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ConclusionThe free body and rigid body modal analyzes clearly show that the built structure is subject to vibrations that can quickly wear out your weld points when the vehicle operates under required conditions for a long time. This problem will be solved by changing the geometry of the cage by placing additional tubes to dampen such frequencies.The collision and rollover assumptions adopted are the worst possible that the team was able to identify. The simulations show that even in these situations the physical integrity of the pilot will be protected although the chassis may suffer irreversible damage.The next steps will gradually transform the vehicle into an agricultural equipment capable of serving small producers who do not need very large machines, but at the same time can no longer use hand tools. For this the design requirements will be more robust to be able to specify a machine that, as in the initial design, is able to walk on extremely rugged terrain and full of obstacles and can pull heavy loads.

SourcesAnsys Costumer Portal(tutoriais sobre o ANSYS). Available in Vehicle Standard (Australian Design Rule59/00 Standards For Omnibus Rollover Strength) 2007. Available in: < https://www.legislation.gov.au/Details/F2012C00535 > REGULAMENTO BAJA SAE BRASIL CAPTULO 7 REQUISITOS MNIMOS DE SEGURANA. Available in: < http://www.saebrasil.org.br/eventos/ProgramasEstudantis/site/baja2011/Arquivos/RBSB%207%20-%20Requisitos%20Minimos%20de%20Seguranca%20-%20Emenda%202.pdf >