Lunar Rover Stress Analysis PDF

 

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Project Report

Group Members: Ahmad Nawab [email protected]   [email protected]

Arslan Saqib [email protected] [email protected]  

Uzair Shakeel [email protected]   [email protected]

Mohammad Ali [email protected] [email protected]  

 

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Table of Contents Turnitin Originality Report

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Introduction ................................................................................................................................................. 3 Methods ........................................................................................................................................................ 4 Drawings, Part Lists and Bill of Materials ............................................................................................... 5 Assumptions................................................................................................................................................. 7 Data Section ................................................................................................................................................. 8 Calculations ................................................................................................................................................. 8 References

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Turnitin Originality Report          

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Processed on: 20-Dec-2019 23:47 PKT

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ID: 1237560216

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Word Count: 1348

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Submitted: 1

final report By Arsalan Saqib  Similarity Index

2% Similarity by Source

Internet Sources: 0% Publications: 0% Student Papers: 2%

1% match (student papers from 18-Oct-2019) Submitted to Colorado School of Mines on 2019-10-18  2019-10-18   1% match (student papers from 27-Apr-2011) Submitted to University of Malaya on 2011-04-27  2011-04-27  ` Project Report Group Members: Ahmad Nawab [email protected] Arslan Saqib [email protected] Uzair Shakeel [email protected] uzairshakeel@roc ketmail.com Mohammad Ali [email protected] [email protected]

Introduction: The goal of the project was to develop dev elop a lunar electric rover and perform a complete stress analysis its body of the rover to ensure that the rover meets the safety requirements and would not fail on its journey to the moon during its time there while keep keeping ing the weight of the rover as minimum as possible. In the following sections, we will explain in detail the assumptions that we made, the list of appropriate materials and their respective  properties, and the complete structural and design analysis of the rover. Reference for the data and information pertaining to the report are mentioned at the end.

Method: Approach:

We first modelled the craft that we were going to shape in SolidWorks which would then be followed by calculations in Math-Cad. Much of the design specifications such as the weight of Chassis and Payload was directly taken tak en from the problem statement. As well as

 

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number of wheels (i.e. 12). Thus, it was ideal to first design the model then adjust and follow-up with calculations.

Engineering Concepts Used:

For analyzing the model, we used a called-out assembly approach in which we analyzed all the parts individually and applied various concepts on it. Our first step was to analyze the cylinder that also carries our payload and astronauts for this we implemented Thin-Walled Vessel analysis by calculating Hoop stresses, radial and longitudinal  stresses. This gave us internal  and its comparison to the external pressure of the vessel. This was then followed by static analysis of Chassis and its cross beams; this was done  by using section and truss analysis learned in the basics of Engineering Statics. These These however represent the constant stresses applied at all times, in order to test the limits of our material body we calculated the maximum stress at the time of impact this was done by assuming that impact occurs at h=0 to simplify the calculations however maximum possible Height (h) for which the spring would be able to sustain the deformation was also calculated.

Technical Research:

Technical research was extensive and constrained by physical limitations such as the material  being able to sustain maximum load while having minimum weight. Thus, all possible calculations were permuted on three distinct materials with different properties to decide what the best material to use would be. The details of said materials is further discussed in Section 3.

Also, for the Chassis we used a standardized W-beam (---------(------------) --) as per the requirement of the  problem statement. In order to compensate for other stresses not anticipated we have hav e chosen a factor of safety of 3  which means that all calculations are done with incorporating the factor of safety in the calculations.

 

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Drawings, Parts List and Bill of Materials: a)  Rendered drawing

 

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 b) Drawing:

c)  Parts List: The parts list is given as follows. The numbers indicated in the drawing symbolize the respective elements on which they the y are written. 1.  Pressure Vessel i.e. the container where the payload pa yload and the astronauts will be staying 2.  Ribs: Ribs are used to create stability and to help uniformly distribute the load of the cylinder on the chassis 3.  Chassis: Chassis consists of W section beam 4.  Wheels: There are 12 wheels in the drawing 5.  Suspension item no

part number

1 2 3 4 5

1 2 3 4 5

description W section Cylinder Rod 150mm diameter Spring Tire

quantity

1 6 6 12

 

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d) Bill of Materials: Pressure Vessel: 

The cylinder in the pressure vessel has a diameter of 1.7 meters, a length o off 2.8 meters, and the two semi-spheres at the end have a diameter of 1.7 meters. Wheels:

The wheels have a diameter of 0.990 meters and a width of 0.35 meters. There are a total of twelve wheels. Chassis:

The chassis has a length of 4.65 meters and a width of 1.622 meters Suspension:

Three different materials were used in case of suspension. There are six springs in the rover each supporting two wheels. Three different springs used: 1.  Music Wire ASTM A228 2.  Hard Drawn ASTM A227 3.  Stainless Steel ASTM A316

Assumptions: We made a few assumptions in order to simplify the calculations during the structural and design analysis of the material.

  To ensure that the rover exceeds the safety requirements even in the most ex extreme treme and

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demanding cases, we performed the analysis anal ysis with a safety factor of 3.0

  The load distribution of the cylinder i.e. the pressure p ressure vessel is assumed to be uniform

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throughout the entire length of the chassis.    No buckling occurs in the pressure vessel, as it is a cylinder   In impact loading, the value of h i.e. the height from which it is dropped is assumed to be 0. However, we do calculate the height from above which if dropped the springs in the suspension would not be able to sustain the impact

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Data Section a)  Materials Data Table Material

Allowable stress (MPa)

Allowable temperature o

Aluminum alloy

420

( C) 350

Stainless steel

520

870

Carbon fiber

450

300

Music wire

500

120

Hard drawn

498

150

 b) Load data In our case the load which we require is 120000N, however the material cannot decide the load, but the appropriate area and safety factor can lead us to the safe way against failure.

Calculations: c)  Loading due to internal Pressurization: The vessel has a thickness ratio i.e. r/t of 42.5 which means that the ccylinder ylinder is a thin cylinder. The calculations for internal pressurization are as follows

 

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d) Buckling of the Module Walls:

We assumed the buckling to be zero since the module is only a cylinder where the pressure of 1 atm is acting from inside out.

e)  Static Loading on the module due to the payload: We assume the loading is uniformly distributed over the entire cross-section of the chassis. First we find the entire weight of the payload. Then we divide it by the total length of chassis to find the distribution of the load per unit length on earth and further the area of the chassis to find the average stress and then we find the bending moment and shear stress diagrams. We do this for all three materials. We will include the diagrams of only aluminium alloy because we found it the most suitable for our module. It is inexpensive when you compare it to carbon fibre and weighs less than Stainless Steel.

 

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 Now, the bending moment diagrams for the beams in the chassis where the material is aluminium is given as belows. These are : For Central Beam:

 

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For Beam 2:

 

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For Beam 3:

 

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For Beam 4:

 

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Impact Loads upon Landing: As already mentioned, we have chosen three springs for suspension.

  Hard Draw   Music Wire   Stainless Steel

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H is assumed as being 0

 

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 Note: These calculations are performed with aluminium as the optimum material. material.

Fatigue Loads:

Figure: S-N curve for aluminum alloy

Figure: S-N curve for stainless steel

 

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Figure: S-N curve for carbon fiber As observed in all of the graphs when 0.3 MPa is observed against number of cycles it almost tends to infinity

Thermal Stresses: The thermal stresses for all three materials at the day and night of moon are shown in the following calculations. The MathCad screenshots for calculations ffor or the thermal stresses stresses are attached below

 

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acceleration/deceleration celeration during take-off take-off and re-entry re-entry g) Loading due to acceleration/de

 

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The following calculations were performed to measure the shear stresses imparted due to launch of the spacecraft that was carrying the rover.

References: Data for springs taken from: https://www.acxesspring.com/compression-spring-calculations.html https://www.acxesspring.com/compression-spring-calculations.html  

Escape velocities on average taken from:

https://www.sciencelearn.org.nz/resources/397-calculating-rocket-acceleration  https://www.sciencelearn.org.nz/resources/397-calculating-rocket-acceleration 

Data Sections taken from: https://www.unitedaluminum.com/chemical-composition-and-properties-of-aluminum-alloys/ 

Details of materials taken from: 

Solid Works Libraries 

Details of W-Beam and Other standard accessories: Solid Works Libraries 

 

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Equations and formulas

Mechanics of Materials Hibbler 6th edition