bolted joints

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Laboratory Report on FE MODELING AND STRESS ANALYSIS OF BOLTED JOINT Submitted to VISVESVARAYA TECHNOLOGICAL UNIVERSITY Jnana Sangama, Belgaum in partial fulfilment of the requirements in Design Engineering Lab II (14MDE26) for the degree of MASTER OF TECHNOLOGY in MACHINE DESIGN Submitted by Sharath B N 1BM14MMD13 Thoufeeque Abdul Rahman Rafique 1BM14MMD15 Under the guidance of Dr. H. K. Rangavittal Associate Professor Mr. Shivashankar R. Srivatsa Assistant Professor

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A Finite Element analysis on bolted joints. Very detailed and contains all the steps with pictures. The analysis has been carried out in SolidWorks. The analysis has also been proofed by SOM approach but there is a large difference due to apparent reasons.

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Laboratory Report on

FE MODELING AND STRESS ANALYSIS OF BOLTED JOINT Submitted to

VISVESVARAYA TECHNOLOGICAL UNIVERSITYJnana Sangama, Belgaum

in partial fulfilment of the requirementsin Design Engineering Lab II (14MDE26) for the degree of

MASTER OF TECHNOLOGYinMACHINE DESIGN

Submitted bySharath B N1BM14MMD13

Thoufeeque Abdul Rahman Rafique1BM14MMD15

Under the guidance of Dr. H. K. RangavittalAssociate ProfessorMr. Shivashankar R. SrivatsaAssistant Professor

Department of Mechanical EngineeringB. M. S. COLLEGE OF ENGINEERINGPB No. 1908, Bull Temple Road, Bangalore 560 019.

May 2015

Sl. No.TitlePage No.

1Introduction03

2Theory04

3Modelling and simulation06

3.1Methodology06

3.2Linear analysis in SolidWorks07

4Problem statement09

5Geometric model and analysis in SolidWorks10

5.1Solid modelling10

5.2Analysis of the bolt and plates11

6Analysis in ANSYS20

7SOM calculations23

8Results25

INTRODUCTIONBolts are one of the most commonly used fastening elements in the assembly of mechanical parts. They are used in almost every engineering application. Structures with bolted joints are usually subjected not only to various static loads but also to impact loads. Because bolts provide localized connection, they lead to high stress concentration in the joined plates. Considering that impact loads are much more damaging at notches, the region around a bolts one of the most critical locations in the plates. Designing for safety requires accurate determination of stress and strain states in the critical locations so that damage done during a crash can be predicted.

A bolted joint by itself is a very complex part considering the complexity of its geometry, the contact between teeth of the bolt and the nut, the pre-tension in the bolt shank, contact surfaces between the nut and the washer, bolt head and the washer, washers and the sheets, bolt shank and the holes of the sheets. Although very complex phenomena can be simulated with todays computational capabilities and commercial finite element codes, proper decisions need to be made regarding the constitutive model, the model of the material, element type, mesh structure, step size, etc. to produce an accurate representation of a physical event. Another difficulty is that given the complexity of a single bolted joint, analysis of panels or beams fastened by many bolts is quite a demanding and time-consuming task. If one tries to simulate the behaviour of such a structure with all its complexity, the results cannot be obtained within a time short enough to be of use in a design process, which requires trials of many configurations to find an effective design. For this reason, the complex geometry should be simplified so as to reduce the computational burden without compromising accuracy.

TheoryTypically, a bolt is tensioned (preloaded) by the application of a torque to either the bolt head or the nut. The preload developed in a bolt is due to the applied torque and is a function of the bolt diameter, length, the geometry of the threads and the coefficients of friction that exist in the threads and under the bolt head or nut. The stiffness of the components clamped by the bolt has no relation to the preload that is developed by the torque. The relative stiffness of the bolt and the clamped joint components do, however, determine the fraction of the external tension load that the bolt will carry and that in turn determines preload needed to prevent joint separation and by that means to reduce the range of stress the bolt experiences as the tension load is repeatedly applied. This determines the durability of the bolt when subjected to repeated tension loads. Maintaining a sufficient joint preload also prevents relative slippage of the joint components that would produce fretting wear that could result in a fatigue failure of those parts when subjected to in-plane shearing forces.The clamp load, also called preload, of a fastener is created when a torque is applied, and so develops a tensile preload that is generally a substantial percentage of the fastener'sproof strength. A fastener is manufactured to various standards that define, among other things, its strength and clamp load.Torque chartsare available to identify the required torque for a fastener based on itsproperty class(fineness of manufacture and fit) orgrade(tensile strength).When a fastener is torqued, a tension preload develops in the bolt and a compressive preload develops in the parts being fastened. This can bemodeledas a spring-like assembly that has some assumed distribution of compressive strain in the clamped joint components. When an external tension load is applied, it relieves the compressive strains induced by the preload, hence the preload acting on the compressed joint components provides the external tension load with a path other than through the bolt. As long as the forces acting on the fastened parts do not exceed the preload, the fastener's tension load will not increase.This however, is a simplified model that is only valid when the fastened parts are much stiffer than the fastener. In reality, the fastener carries a small fraction of the external tension load even if that external load does not exceed the clamp load. When the fastened parts are less stiff than the fastener (those that use soft, compressed gaskets for example), this model breaks down and the fastener is subjected to a tension load that is the sum of the tension preload and the external tension load.In some applications, joints are designed so that the fastener eventually fails before more expensive components. In this case, replacing an existing fastener with a higher strength fastener can result in equipment damage. Thus, it is generally good practice to replace old fasteners with new fasteners of the same grade.

MODELING AND SIMULATION:MethodologySOLIDWORKS is asolid modeler, and utilizes aparametric feature-basedapproach to create models and assemblies. The software is written onParasolid-kernel.Parametersrefer to constraints whose values determine the shape or geometry of the model or assembly. Parameters can be either numeric parameters, such as line lengths or circle diameters, or geometric parameters, such as tangent, parallel, concentric, horizontal or vertical, etc. Numeric parameters can be associated with each other through the use of relations, which allows them to capture design intent.Design intentis how the creator of the part wants it to respond to changes and updates. For example, you would want the hole at the top of a beverage can to stay at the top surface, regardless of the height or size of the can. SOLIDWORKS allows the user to specify that the hole is a feature on the top surface, and will then honor their design intent no matter what height they later assign to the can.Featuresrefer to the building blocks of the part. They are the shapes and operations that construct the part. Shape-based features typically begin with a 2D or 3D sketch of shapes such as bosses, holes, slots, etc. This shape is then extruded or cut to add or remove material from the part. Operation-based features are not sketch-based, and include features such as fillets, chamfers, shells, applying draft to the faces of a part, etc.Building a model in SOLIDWORKS usually starts with a 2D sketch (although 3D sketches are available forpower users). The sketch consists of geometry such as points, lines, arcs, conics (except the hyperbola), and splines. Dimensions are added to the sketch to define the size and location of the geometry. Relations are used to define attributes such as tangency, parallelism, perpendicularity, and concentricity. The parametric nature of SOLIDWORKS means that the dimensions and relations drive the geometry, not the other way around. The dimensions in the sketch can be controlled independently, or by relationships to other parameters inside or outside of the sketch.In an assembly, the analog to sketch relations are mates. Just as sketch relations define conditions such as tangency, parallelism, and concentricity with respect to sketch geometry,assembly matesdefine equivalent relations with respect to the individual parts or components, allowing the easy construction of assemblies. SOLIDWORKS also includes additional advanced mating features such as gear and cam follower mates, which allow modeled gear assemblies to accurately reproduce the rotational movement of an actual gear train.Finally, drawings can be created either from parts or assemblies. Views are automatically generated from the solid model, and notes, dimensions and tolerances can then be easily added to the drawing as needed. The drawing module includes most paper sizes and standards (ANSI,ISO,DIN,GOST,JIS,BSIandSAC).

Linear analysis in solidworks: Linear stress analysis withSOLIDWORKS Simulationenables designers and engineers to quickly and efficiently validate quality, performance, and safetyall while creating their design.Tightly integrated with SOLIDWORKS CAD, linear stress analysis using SOLIDWORKS Simulation can be a regular part of your design process, reducing the need for costly prototypes, eliminating rework and delays, and saving time and development costs.Linear stress analysis calculates the stresses and deformations of geometry given three basic assumptions:1. The part or assembly under load deforms with small rotations and displacements2. The product loading is static (ignores inertia) and constant over time3. The material has a constant stress strain relationship (Hookes law)SOLIDWORKS Simulation usesfinite element analysis(FEA) methods to discretize design components into solid, shell, or beam elements and uses linear stress analysis to determine the response of parts and assemblies due to the effect of: Forces Pressures Accelerations Temperatures Contact between componentsLoads can be imported from thermal, flow, and motion Simulation studies to perform multiphysics analysis.In order to carry out stress analysis, component material data must be known. The standard SOLIDWORKS CAD material database is pre-populated with materials that can be used by SOLIDWORKS Simulation, and the database is easily customizable to include your particular material requirements.

PROBLEM STATEMENTAIM:Finite element modelling and failure analysis of bolted joints

To understand the material stress distribution that occurs in a bolted joint, FE modelling and failure analysis has been done using CAE tool Solidworks and obtained results are tabulated.

Geometric model and analysis in SolidWorksSolid modellingThe solid model considered along with the loading and boundary conditions for the bolted joint analysis is shown below. The middle plate is held rigidly at one end while a load of 5kN each is applied on the opposite ends of the upper and lower plates. The three plates are held together by an M10 bolt.

2-D drawing of the above assembly with the dimensions is as shown below.Analysis of the bolt and plates1. Upper/lower plateMaterial: Alloy steel - Properties

Solid model.Half-model of the plate

Since the model is symmetric, half of the model is built and symmetric boundary condition is applied along the plane of symmetry.

Boundary conditions and loadsFixed boundary condition where the bolt comes into contact with the plateApplied load Symmetric boundary condition

Along with the symmetric boundary condition as mentioned before, a section of the hole where the bolt makes contact with the plate is constrained, shown by Green arrows. The angle of surface contact considered here is 800; the data was obtained from Hand Book of Bolts and Bolted joints by John Bickford and Sayed Nassar. A load of 5000 N is applied at the end of the plate, shown by Pink arrows.Analysis - Von-Mises stress

Iso clipping of the Von-Mises stress

From the Iso clipping it is seen that the average Von-Mises stress over the plate obtained is around 130 Mpa, considering the errors due to meshing and boundary conditions.Deformation plot

Maximum deformation obtained is 6.0e-3 mm.

2. Middle-plateMaterial: Alloy Steel - Properties

Solid model.Half-model of the plate

Since the model is symmetric, half of the model is built and symmetric boundary condition is applied along the plane of symmetry.

Boundary conditions and loadsApplied load Symmetric boundary conditionFixed boundary condition where the bolt comes into contact with the plate

A section of the hole where the bolt makes contact with the plate is loaded with a force equal to 10000 N shown by Pink arrows, which is a sum of the loads applied to the upper and lower plates. In the middle plate, the bolt comes into contact with the plate hole on the opposite surface in comparison with the upper and lower plates. The end surface is given fixed boundary condition, which is represented by Green arrows.Stress - Von-Mises--Iso clipping of Von-Mises Stress

From the Iso clipping it is seen that the average Von-Mises stress over the plate obtained is around 220 Mpa.Deformation plot

Maximum deformation obtained is 1.5e-2 mm.

3. BoltMaterial: Ti-8Al-1Mo-1V Annealed - Properties

Solid ModelSurface area in contact with middle plateSurface area in contact with lower plateSurface area in contact with upper plate

A bolt of 10mm diameter is considered. The surface area of the bolt which comes into contact with the plate is also modelled into the bolt, as shown.

Boundary conditions and loadsApplied load Applied load Fixed boundary condition where the bolt comes into contact with the plate

The surface area which comes into contact with the middle plate is constrained, represented by Green arrows and a load of 5000 N is applied on each of the two surfaces which comes into contact with the upper and lower plates. This load is represented by Pink arrows. Stress - Von-Mises

Iso clipping of Von-Mises Stress

From the Iso clipping it is seen that the average Von-Mises stress over the bolt obtained is around 300 Mpa.

Analysis in Ansys1. Upper/lower plateVon Mises StressAverage Von Mises stress obtained = 123 MPaTotal deformation

2. Middle plateVon Mises StressAverage Von Mises stress obtained = 233 MPaTotal deformation

3. BoltVon Mises Stress

Average Von Mises stress obtained = 307 MPaDeformation

SOM calculationsThe bolt and plate are subjected to various stresses upon loading. But in the Strength of Materials approach, the boundary and loading conditions are simplified to a great extent by considering various assumptions. The stresses considered for the plates and the bolt is given below.In our bolt and plate configuration, the bolt is subjected stresses due to double shear about the cross section because of the two plates and is also subjected to crushing stress along the cylindrical face where the surfaces of the plate and bolt are in contact. The plate is subjected Tearing stress.Stress due to double shearType of bolt used is Metric bolts Data taken from Bolt grade marking and strength chartBolt properties:Class 10.9 Alloy steel, quenched and temperedYield strength, y = 940 MPaAccording to maximum shear stress theoryy = y = y = 470 MPaThe bolt is subjected to double shear as shown in the figure

The shear stress on the bolt is given by the formula = F/2Ab = (10*103)/(2*102/4) = 63.66 MPaFactor of safety for the bolt is given byFOS = y/ FOS = FOS = 7.38Generally bolts are designed to maintain a factor of safety in the range of 5-10.But in the Finite Element model, the analysis is conducted by considering the load on the cylindrical surface of the bolt. But in the above analytical approach, the shear load is assumed to be acting on the cross-section of the bolt as shown in the figure. Hence a correlation between the Von-Mises stress on the bolt obtained by FEA and the crushing/bearing stress from SOM approach is more appropriate. Crushing stress, c = +2XWhere d: diameter of the bolt, t: thickness of the section of the bolt which is in contact with the plates, considered for each plate individually. F1: force acting on centre of the bolt, F2: force acting on top/bottom of the boltc = + 2X = 200 Mpa Factor of safety is given by,FOS = FOS = FOS = 4.7But the Von-Mises stress obtained from FEA is 300 Mpa. This difference is due to the difference in boundary conditions between the two approaches.

Results

Analysis methodYield stressVon-Mises stress

Plate - Alloy steelBolt - Titanium alloyPlateBolt

SolidWorks

620.42 MPa

930.79 MPa220 Mpa300 MPa

ANSYS Workbench233 Mpa307 MPa

The results obtained from the analysis of the bolted joints have been presented in the table above. It is seen that the Von-Mises stress values are lower than the stress at yielding point, and hence the design is safe.

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