Page 1 of 3 ME1332: Design Project 1 for B-Teams – Land Rover Car Chassis Design 1. BACKGROUND A car chassis can be of a truss framework structure for combining lightness and strength. During driving the chassis is loaded by the passenger loading plus inertia of the engine and the reactions through the wheels. Jaguar Land Rover has approached you to do a feasibility study for a new concept Land Rover 4x4. 2. THE CHALLENGE Your team is to design, build and test a suitable Land Rover scale model chassis structure based on a balsa wood truss construction to fit the test rig. Each team member must show an updated logbook at each Design Lab session in order to demonstrate their contribution to each of the following: Model chassis A scale balsa wood model will be built and tested in order to compare with the predicted load capacity of the chassis. Limited material quantities will be issued to teams: 2.1 Generate a Specification that includes criteria for selecting the best design. 2.2 Design a truss framework having maximum load capacity/minimum weight (see 2.12) with the loads at the positions shown in Figure 1. Your structure must remain within the outer envelope and outside the apertures but does not have to follow these lines. The two truss sides are joined by cross-members that must be perpendicular to the truss and whose mass is to be accounted for. There must be sufficient cross-members to prevent twisting of the structure. 2.3 Use truss analysis to predict the load at which the truss will fail under the testing procedure described in Section 4. Each member of the team should propose and analyse their own truss design proposal, including calculations of the estimated model weight and estimated failure load. The maximum load that will be applied is 100N. Loads will be applied using weight hangers at the points indicated in Figure 1. 2.4 Buckling of the framework struts is the most likely failure mode and in order to manage this, you may need to increase the stiffness of the framework members under compression or reduce their length. The buckling loads for members under compression may be calculated using the Euler strut buckling formula: 2 2 2 L EI P = P π (1) Where P is the buckling load; E is the modulus of elasticity for the material; I is the smallest second moment of area of the section; L is the length of the strut; and P2 is a constant which depends on the type of end supports for the strut. In a strut pin jointed at both ends, P2 = 1 but you must research the value applicable to your design. 2.5 Assess the effect of geometric uncertainty as described in the lecture sessions, i.e. the effect of variations in dimensional tolerances on predicted failure. 2.6 Select the best design based on objective quantified selection criteria and improve the selected design, possibly combining it with ideas coming from the other unselected designs. 2.7 Produce a TECHNICAL DRAWING of the final design including the predicted failure load and mass. If additional calculations are required to predict failure load and mass, because of the improvements made with respect to the selected design, do not report the calculations (but include the predicted values). 2.8 Construct your model using the balsa wood, materials and tools supplied. All the construction work must be performed within the timetabled hours. See relevant workshop technician for availability. 2.9 Provide string loop mountings at the loading points shown in figure 1, on which to attach weight hangers. Ensure that you have strong loading points and that the hangers will not bottom-out on the test rig. Ensure that the loading points conform to the positions defined in Figure 1. 2.10 The apertures for driver and passenger access must be as per the dimensions in Figure 1. 2.11 Return all equipment issued and, if you wish, add a team logo/name to the model!Page 2 of 3 2.12 The framework will be weighed prior to the start of the test and will be loaded until failure occurs. The performance will be assessed according to the following performance factor, PF: (2) Where, using the same units as above: delta = (actual load - calculated load)2 + 2* (calculated mass - actual mass)2 Therefore PF is a larger-the-better measure and it penalises model frameworks that are not accurately predicted in terms of mass and strength. The maximum allowable mass is 50g and the minimum strength requirement is 30N. Frameworks that fail to carry the 30N load or have a mass more than 50g will be disqualified and will score zero PF. Also, the PF will be penalised if points 2.2/9/10/11 are not correctly addressed. Balsa wood Material issued to each team will be limited to: (i) 3.2 mm x 3.2 mm square x 914mm = 6 lengths. (ii) 3.2 mm x 6.4 mm rectangular x 914mm = 10 lengths. (iii) 1.6 mm x 76 mm flat sheet x 914mm (joints only, not to be used in place of truss structure) = 1 length. (iv) Important! You must allow for wastage as no further material will be issued. Table 1: Typical mechanical and physical properties of balsa wood Density [kgm-3] Young's modulus [MNm-2] Tensile strength [MNm-2] Shear strength [MNm-2] Along Grain 150 3100 15 2 3. REPORTS (70%) • SUBMITTED IN THREE STAGES: all sections are assessed and feedback generated after the latter deadline. Marks are only awarded to the students identified on each relevant page. • DO NOT EXCEED MAX page numbers shown. Use Arial, Calibri or Times New Roman, 10-point or larger. • All sketches must be clear and can be hand drawn. Technical drawings must be to BS8888. • Calculations must be clearly laid out where specified - typed not hand written. • Report to be on A4 paper, stapled in the top LH corner (no covers, plastic wallets etc.) and the pages numbered. Excess pages will not be read or marked. Deadline for Assignment B: Part B1 (Individual) is 12:00 Friday 3rd FEBRUARY 3.1 Individual author name+ID+TEAM identified in header. Proposed truss design and analysis, including calculations of forces, model mass and failure load estimations, and respective geometric uncertainty calculations. Including framework design (to BS8888). References. (2 pages per student). Deadline for Assignment B: Part B3 (Individual) is 12:00 Wednesday 15th FEBRUARY 3.2 Author name+ID+TEAM identified in page header. Individual team members will also submit their (typed) record of contributions made to Project 1 team meetings by all team members. (1 page) model actual mass (g) 100 model failure load (N) = × delta PFPage 3 of 3 4. MODEL TEST DAY (30%) – Monday 13th FEBRUARY during your designated Design Lab This is the deadline for Assignment B: Part B2. Only contributing team members in attendance will receive this mark. Group presentation before testing. Three-minute presentation giving quantitative evaluation of design solutions and rationale for an improved design. State predicted failure load and mass of structure. Test: The model will be placed on two supports having a gap of 600 mm and each approx 30 mm wide. Loads of 10 N will be applied at the points B, C and D (see Figure 1). Points B, C and D correspond to the load during overturning; driver/passenger/luggage loading; and the load of the motor/transmission assembly. Access to the driver and passenger space is shown and these must be apertures through the structure. The chassis is 100mm to 200mm wide. The front door is an identical mirror image of the rear door. Figure 1: Land Rover model chassis with loading points (point B must be above head height) 4.1 One balsa wood model per design group must be submitted for testing in accordance with Sections 2 and 4. 4.2 You must make sure that suitable mounting points for the weight hangers are available. Cord loops at points B, C and D on the framework are suggested but test to see if they are satisfactory. Also, check that the the access for the driver and passengers agree with Figure 1. 4.3 The framework should support the loads applied for at least 10 seconds. 4.4 Beyond 30N, additional loads at point C will be added until the framework collapses, up to a maximum load of 100N. If failure does not occur at this load then a nominal value of 130 N will be recorded as the failure load, hence designs which would have had a failure load much higher than 130N will be indirectly penalised. 4.5 The total load before collapse will be recorded and then the performance factor PF will be evaluated. 4.6 The group which achieves the highest performance factor PF will be declared the winner. 4.7 Marks for testing of the balsa wood model will be allocated in accordance with the PF achieved. Individual log books will be regularly inspected (rear axle) D A B E (front axle) C Body width is 100 min - 200 max (for loading integrity)