solid lab

SKMM3941-CAR STRUCTURE ANALYSIS (BENDING CHARACTERISTIC) MAKMAL III SEM 2 2014/2015

CAR STRUCTURE ANALYSIS (BENDING CHARACTERISTIC)1. TITLECar Structure Analysis (Bending Characteristic)

2. INTORDUCTIONA car is a wheeled, self-powered motor vehicle used for transportation. Most definitions of the term specify that cars are designed to run primarily on roads, to have seating for one to eight people, to typically have four wheels, and to be constructed principally for the transport of people rather than goods. Cars did not become widely available until the early 20th century. Cars are equipped with controls used for driving, parking, and passenger comfort and safety. New controls have also been added to vehicles, making them more complex. Examples include air conditioning, navigation systems, and in car entertainment. Most cars in use today are propelled by an internal combustion engine, fuelled by deflagration of gasoline (also known as petrol) or diesel.

Cars are expected to perform very high in acceleration, braking, handling, aesthetics, ergonomics, manufacturing and maintenance within minimum manufacturing cost with no compromise on driver safety. The car must also satisfy safety requirements such as side impact protection and impact attenuator. Finally the cars are judged on the basis of performances during static and dynamic events including technical inspection, business presentation, cost, design, endurance tests. In designing this test rig, the total loads from the vehicle structure have been identified under bending and torsion case. The test rig function to produce the torsion and bending case and the loads is measured by using the load cell.

Before the car is produced, many test had been conducted by the researcher in automobile industries to achieve some standards and for customers safety and satisfaction. One of the tests that are being conducted is a car structure bending test. This test is conducted to measure the vehicle strength and stiffness on a static bending case of the vehicle structure. To test the car for bending test, researcher used Test Rig for bending on vehicle. This method has been widely used. By using that rig, an artificial situation of bending can be produced. Moreover, the load and the stiffness of the vehicle can be measured for static bend condition.

Proton Holdings Berhad is a Malaysia automobile manufacturer. The second generation Proton Saga, also called the saga BLM launched on 18 January 2008 is one of the Proton products. Previously, the first generation Proton Saga was Protons most successful model, having a 23 years long span. In this experiment, we will determine the bending of the car structure of the most popular car model among Malaysian.

3. OBJECTIVE1) To investigate and determine the bending stiffness of saga BLM car structure.2) To analyse the maximum deflection and maximum stress the car structure.3) To determine the critical point due to bending effect.

4. SCOPE1) Analysis the maximum deflection and maximum stress the car structure is able to withstand.2) Only bending effect is considered.3) Understanding on principal of bending characteristic on vehicle structure.4) Study of structural design and analysis.

5. EQUIPMENTName of EquipmentFigures

Saga BML body structure.

Three of Dial gauge

Measuring tape

6. THEORYIn designing the bending characteristic of car structure, the specifications such as functions, design requirements and evaluation criteria must be defined clearly. According Mott (2004), functions tell what the device must do, using general, non-quantitative statements that employ action phrases such as to support a load, to lift a crate, to transmit power or to hold two structural members together. Moreover he said, design requirements are detailed, usually quantitative statements of expected performance levels, environmental conditions in which the device must operate limitations on space or weight or available materials and components that may be used. Whereas, evaluation criteria are the statements of desirable qualitative characteristics of a design that assist the designer in deciding which alternative design is optimum- that is, the design that maximizes benefits while minimizing disadvantages.Based on Mott (2004), there are three basic fundamental kinds of stress; tensile, compressive and shear. Tensile and compressive stress, called normal stresses, are shown acting perpendicular to opposite faces of the stress element. Tensile stresses tend to pull on the element whereas compressive stresses tend to crush it. Shear stresses are created by direct shear, vertical shear in beams or torsion. In each case, the action on an element subjected to shear is a tendency to cut the element by exerting a stress downward on one face while simultaneously exerting a stress upward on the opposite, parallel face. Stress can be defined as the internal resistance offered by a unit area of a material to an externally applied load. = force/area = F/AIn Applied mechanics, bending (also known as flexure) characterizes the behaviour of a slender structural element subjected to an external load applied perpendicularly to a longitudinal axis of the element. The structural element is assumed to be such that at least one of its dimensions is a small fraction, typically 1/10 or less, of the other two. When the length is considerably longer than the width and the thickness, the element is called a beam. For example, a closet rod sagging under the weight of clothes on clothes hangers is an example of a beam experiencing bending. On the other hand, a shell is a structure of any geometric form where the length and the width are of the same order of magnitude but the thickness of the structure (known as the 'wall') is considerably smaller. A large diameter, but thin-walled, short tube supported at its ends and loaded laterally is an example of a shell experiencing bending. In the absence of a qualifier, the term bending is ambiguous because bending can occur locally in all objects. Therefore, to make the usage of the term more precise, engineers refer to a specific object such as the bending of rods, the bending of beams, and the bending of plates, the bending of shells and so on.For this experiment, we are to simply analyse the effects of bending stress on a vehicular structure. In the analysis of vehicular structures, the analysis can be simplified into beam type elements. Here, the bending stiffness of a beam can be derived from the beam deflection equation when the beam is subjected to a force. Bending stiffness (K) here refers to the resistance of a member towards deformation caused by bending. K is a function of the elastic modulus E, the area moment of inertia I of the respective beam cross-section about the axis of interest, beam boundary condition and also the length of the beam.

P in the above equation refers to the applied force whereas w refers to the deflection of beam. When we take a look at the elementary beam theory, we find that the relationship between the applied bending moment M, and the resulting curvature K of the beam is:

W here refers to the deflection of the beam whereas x refers to the distance along the beam of interest. Integrating the above equation twice yields the computation for the deflection of the beam. Generally, bending stiffness in beams is also known as flexural rigidity.In this experiment, we consider the case to be simple beam bending. The conditions and assumptions for using simple bending theory are as follows: The beam is subject to pure bending. This means that the shear force is zero, and that no torsional or axial loads are present. The material is isotropic and homogeneous. The material obeys Hooke's law (it is linearly elastic and will not deform plastically). The beam is initially straight with a cross section that is constant throughout the beam length.

The beam has an axis of symmetry in the plane of bending. The proportions of the beam are such that it would fail by bending rather than by crushing, wrinkling or sideways buckling. Cross-sections of the beam remain plane during bending. Deflection of a beam deflected symmetrically and principle of superposition

Based on Mott (2004), a beam is a member that carries loads transverse to its axis. Such loads produce bending moments in the beam, which result in the development of bending stresses. Bending stresses are normal stresses, that is, either tensile or compressive. The maximum bending stress in a beam cross section will occur in the part farthest from the neutral axis of the section. Compressive and tensile forces develop in the direction of the beam axis under bending loads. These forces induce stresses on the beam. The maximum compressive stress is found at the uppermost edge of the beam while the maximum tensile stress is located at the lower edge of the beam. Since the stresses between these two opposing maxima vary linearly, there therefore exists a point on the linear path between them where there is no bending stress. The locus of these points is the neutral axis. Because of this area with no stress and the adjacent areas with low stress, using uniform cross section beams in bending is not a particularly efficient means of supporting a load as it does not use the full capacity of the beam until it is on the brink of collapse. The formula we used for determining the bending stress in a beam under simple bending is as follows:

Where, The bending stressM - The moment about the neutral axisy - The perpendicular distance to the neutral axis- The second moment of area about the neutral axis x

Positive bending occurs when the deflected shape of the beam is concave upward, resulting in compression on the upper part of the cross section and tension on the lower part. Conversely, negative bending causes the beam to be concave downward. When the dimension is already fixed, the yield strength of the material can be change to make sure the design will not failed due to bending at specify force. So, by using the dimension, calculate the moment of the beam. Then calculate the stress due to the bending and compare it with yield strength of the material. If the stress due to bending is smaller than yield strength of material, thus it mean that the beam dimension with the material used will not failed if the specify force is applied.

7. PROCEDURE1) The aim of this experiment is to determine the bending moment experienced by one vehicle (car structure). Therefore, the parameters involved are the deflections (in mm) occurring at a chosen section of the car structure.2) The total length (in mm) of the chosen section of the car structure is measured using a measuring tape and three points were appointed along that section. Figure 7.1 below show the apparatuses set up for the experiment.

Figure 7.1

3) In order to conduct this experiment, three dial gauges are used which are accurate to within 1 mm. One dial gauge is placed approximately under the each of the three points. Figure 7.2 below demonstrates how the apparatuses are prepared and set up for the experiment.

4) The three dial gauges are adjusted manually to show zero value before the loads are applied onto the vehicle as shown in Figure 7.3 below.

Figure 7.25) A sample load 50kg (human weight converted to force in Newton) of 490.50 N is applied as a pointed load and the deflection experienced is monitored and recorded.

Figure 7.36) Step 4 and 5 are repeated but by replacing the applied sample load with a heavier load.7) The experiment is stopped after the fifth load is applied.8) From the data collected, we are able to determine the moments and stresses by calculation.9) Every data collected are tabulated.

8.0 EXPERIMENTAL DATAForce(N)Deflection (mm)Maximum Deflection (mm)Distance, x (mm)Moment, M (Nm)Stress (kPa)Maximum Stress (kPa)

490.50(50 kg)

1520396194.24189.90570.67

17793388.97380.29

201190583.70570.67

17793388.97380.29

15396194.24189.90

686.70(70 kg)2229396271.93265.86798.93

24793544.55532.39

291190817.17798.93

24793544.55532.39

22396271.93265.86

1177.2(120 kg)3240396466.17455.761369.60

36793933.52912.68

4011901400.871369.60

36793933.52912.68

40396466.17455.76

1667.7(170 kg)4059396660.41645.671940.26

477931322.491292.97

5911901984.561940.26

477931322.491292.97

40396660.41645.67

2158.2(220 kg)5874396854.65835.572510.93

607931711.451673.24

7411902568.262510.93

607931711.451673.24

58396854.65835.57

9.0 SAMPLE OF CALCULATION9.1 Free body diagram (using MDSolids software)

Figure 9.1: Load Diagram

9.2 Shear diagram (using MDSolids software)

Figure 9.2: Shear Diagram

9.3 Moment diagram (using MDSolids software)

Figure 9.3: Moment Diagram

The calculation of maximum bending moment:LOAD = 490.50 N AT POINT 3 m

10.0 GRAPH The graph between Deflection versus Load Applied

The graph between Maximum Deflection versus Force Applied

The graph between Maximum Stress versus Load Applied

The graph between Maximum Stress versus Maximum Deflection

11.0 DISCUSSIONThe first graph of deflection versus applied load is displaying the values of deflection (in mm) on the car structure against the load applied (N). Based the graph plotted, we have observed how the three points react to the load applied which deflection of point 1 and 5,and deflection of point 2 and 4 are same value and distance. The experiment show that every deflection of point 3 at every load be applied showed the highest deflection. It means the critical point located at point 3 that distance from the datum is 1190 mm. In addition, this may due to the fact that it is located in the middle of the structure and also where the load is applied directly. The second slope represents points 2 and 4 where a lower value of deflection compare to deflection point of 3 occurs. These points are subjected to the same load but they are located an equal distance away on either side of point 3, therefore the deflection on point 2 and 4 are less than point 3 which the distance is 793 mm from datum. The last slope represents point 1 and 5 and they experience the lowest value of deflection because they are located on the ends of either side of the structure. It show that the deflection at this point does not critical which the distance is 396 mm from datum. All three deflection point prove that when the deflection increases, the load applied is increased also. Show that the graph is directly proportional.From the second graph of the values of maximum deflection (m) plotted against the applied load (N). From the experiment, we have observed that point 3 which is located in the middle of the structure has the highest length of deflection which is 1190 mm. Hence, we can conclude that the maximum deflection at point 3 that located at the middle structure of car. As we can seen from the plotted graph, the maximum deflection occurring increases greatly and steadily as the load applied is added. Thus, when the increase of the load applied, the increase of the maximum deflection (m). We can assume that, the graph maximum deflection is directly proportional to applied load.The third graph involves the maximum stress (kPa) versus the load applied (N). Before that, we can figure out that the maximum stress should at critical point. In this case, the critical point occurs at point 3. It because, when the deflection is increase, the maximum stress also increase. As we have stated, the maximum deflection occurs at point 3 (middle point) and thus, the maximum stress will also occur at this point which the highest reading is 2510.93 kPa. By the looks of the values plotted, the maximum stress of this structure rises steadily as the load applied is continuously increased five times. It show the graph maximum stress is directly proportional to load applied.The fourth graph is maximum stress (kPa) plotted against maximum deflection (mm). Based on the graph, the maximum stresses occurring are directly proportional to the maximum deflection. It show that when we increase the deflection at critical point, it will make the stress be applied toward the point is increase. Therefore, on this critical part, the manufacture should use the suitable material for safety factor of the car. From our observation, this is due to the fact that the applied load was applied throughout the experiment at correct position of the car.

12.0 CONCLUSIONAs conclusion, this experiment is to analyse and determine the bending stiffness experienced by a car structure as well as discovering the critical point on the structure which the objective of this experiment that must be achieved it. Based on the experiment we have conducted, we have observed how the structure has reacted towards various applied pointed loads. Otherwise, the loads have caused bending moment and a measurable deflection. Therefore we were able to achieve the first objective. In other hand, we had achieved the second objective to determine the critical point due to bending effect. From the data and graph be plotted, we can figure it the critical point at deflection of point 3 (middle structure of car) which the distance is 1190 mm from datum.

13.0 REFERENCES Donald E. Malen, (2012), Fundamentals of Automobile Body Structure Design, SAE International. Kaukert Boonchukosol, (2017), Vehicle Structure Analysis. Bending and Torsion Presentation. R.C.Hibbeler, (2013), Flexural rigidity and curve deflection theory, Mechanics of Materials, Ninth Edition. http://www.comsol/blogs/computing-stiffness-linear-elastic-structures-part-1/ http://www.doitpoms.ac.uk/tlplib/thermal-expansion/printall.php http://www.hindawi.com/journals/tswj/2014/190214/