GROUP 5 PRESENTATION

GROUP

Presentation of Group 5

BSRE IV-2

railway vehicle dynamics

CONTENT:

1. Suspension Elements and Mode of Vibrations

2. Rail Profile and Wheel Profile

3. Contact Condition

4. Steady State Curving Behavior

suspension elements and modes of vibration

Reporter: Joyce Carmelo

Car body

Air Spring (Secondary Suspension)

Primary Suspension

Bogie

suspension elements and modes of vibration

• The railway vehicle in general comprises a car body supported by two bogies one at each end.

• Bolsters are the intermediate members between the car bodies. Each bogie frame is connected to car body through side bearings.

TYPES OF suspension

1. pRIMARY suspension

2. SECONDARY suspension

suspension of elements

The suspension of elements should ensure equal and uniform distribution of the loads through the components of the rail vehicle body to the track and should minimize the dynamic loads.

Secondary SUSPENSION

PRIMARY SUSPENSION

The secondary suspension interconnects the carbody and bogie, with the purpose of isolating the carbody from excitations transmitted from track irregularities via the wheelsets and bogie frames. The air spring is part of the secondary suspension of most modern passenger rail vehicles, placed between the carbody and bogie.

The primary suspension consists of spring and damper components between the bogie and the wheel set, in order to secure a stable running behaviour, and also to ensure low track forces, low wear and good behaviour in curves.

PRIMARY SUSPENSION

Secondary SUSPENSION

1. increased stiffness for increased preload,
2. height independent of preload due to level control,
3. significant horizontal stiffness,
4. low height,
5. good sound and vibration isolation.

modes of vibration

• Longitudinal (Roll)
• Vertical (Yaw)
• Lateral (Pitch)

Rail Profile And Wheel Profile

Reporter: Jerald Magtahas

RAIL PROFILE

The weight of a rail per length is an important factor in determining rail strength and hence axle loads and speeds.

RAIL PROFILE

Rails are made in a large number of different sizes. Some common European rail sizes include: • 40 kg/m (81 lb/yd) • 50kg/m (101 lb/yd) • 54kg/m (109 lb/yd) • 56kg/m (113 lb/yd) • 60g/m (121 lb/yd)

TYPES OF RAILS

1. Flat Bottom – Vignole railway

Flat bottomed rail is the dominant rail profile in worldwide use. Vignoles rail is the popular name of the flat-bottomed rail, recognising engineer Charles Vignoles who introduced it to Britain.

The cut length and shorten length of rails are agreed by purchaser and manufacturer. Rails are delivered in theoretical weight. The density of 7.85g/cm3 is applied to calculate the rail theoretical weight.

2. CRANE RAILS

Symmetrical and having a flat bottom, their biggest difference to normal railway rails is their weight and much thicker web. This is needed to support very large axle loads from crane vehicles.

3. CHECK RAILS

•Trains run against them in areas where extra steering forces for the axles may be needed, such as very sharp curves or to provide additional safety when a switch and crossings. They essentially restrain the flat back of the wheel to direct it around sharp curves or to the correct route set at switches and crossings.

4. grooved rails

•Trains run against them in areas where extra steering forces for the axles may be needed, such as very sharp curves or to provide additional safety when a switch and crossings. They essentially restrain the flat back of the wheel to direct it around sharp curves or to the correct route set at switches and crossings.

wheel profile

Railway Wheels

Railway wheel is assembly of two wheels fixed to the axle by interference fit and they rotate along with the axle

These wheels are provided with flange towards the inner side, which guide the wheels to travel on the rails and does not allow it to fall down from the rails

Railway Wheel parts

1. Hub2. Disc 3. Tyre

Railway Wheel parts

1. Hub-Hub is the centre portion of the wheel, where the wheel is fixed to the axle by means of interference fit.

Railway Wheel parts

2. Disc-This portion is the thinnest portion of the wheel as it does not come in contact with rail nor it is coming in contact with the axle.

Railway Wheel parts

3. Tyre -Tyre is the portion in contact with the rail, which wears out in service. The profile of the tyre is significant forsafe running of the trains.

wheel profile

• The “wheel profile” refers to the thickness of the wheel. Wheel profile measurement is the measurement of the thickness of the wheel. • Over time the wear and tear on railway wheels can affect the quality of them and have an impact on the interaction between the wheels and the rails. • Worn and damaged wheels can cause the railway vehicles to become uncomfortable or even unsafe.

contact surface of the rail and wheel

Reporter: Xavier Rei Retorta

• The first area is for the motion of straight lines and the conical coefficient, 0.15 to 0.2 for passenger trains • The second area is for passing through the normal arcs and needs to have a conical coefficient of 0.2–0.6 in the region • in the third area higher values are required

Contact Area A (The Central Rail and Profiles Crown Center)

• Contact stress between wheel and rail is lower than in other areas.
• Longitudinal creep forces are larger compared to the side creep forces.
• Crown wheel depression occurs due to wear.

Contact in Area B (Contact Between the Inner Edge of the Track and Wheel Flange Arc)

• High contact stresses.
• Wear of the inner surface of the outer arc rails.
• High side creep and sharp flange.
• This area is most important in determining the life of the wheels and rails.

Conformal Contact

Single Contact Point

Two Contact Point

Contact Zone C (Between the End of the Crown Wheel and the Crown of the Rail)

• High contact stresses due to the contact of the end of the crown wheel with the rails.
• Completion of the contact before the virtual wheel flange meets the end of the crown.

WEAR IN VARIETY OR RAIL LINES

Wear in Straight Lines• Rolling friction of the wheels and the rails on the side of the cap causes wear in rails in straight lines and can make the most of this type of wear vertical resulting in reduction in rail height.Wear in Curved Lines• moving in severe arches causes flange deterioration. If the slope width is less than the balance, the outer rails bear greater loads and rail rolling risk or the wheel coming off the rail is increased.

WEAR MECHANISMS

Abrasive Wear (Scratch)• Abrasive wear occurs when a hard surface is rubbed against a soft surface and by penetration, causing a track on the soft surface. Adhesive Wear• Adhesive wear occurs if there is local slip between two surfaces in the joints and, eventually, causes failure by the transfer of material from one surface to the other• Formation and breaking of molecular bonds that are in contact with two levels of slipping contact Delamination Wear• Delamination wear can cause microscopic wear.

WEAR MECHANISMS

Tribochemical Wear• This type of wear on contact surfaces results from reactions with the environment. The surrounding environment can be in the state of gas or liquid Fretting Wear• Fretting wear is caused when two surfaces would have tangential and oscillating movements under the applied loads with low relative amplitudes and the slip is caused by vibratory or cyclic stresses

WEAR MECHANISMS

Surface Fatigue Wear • Surface fatigue is a phenomenon caused as a result of the effects of stress fluctuations under the condition which two solid materials have sliding contact Impact Wear • Impact wear can be produced when a solid surface is continuously in contact with another solid surface.

PARAMETERS ON WHEEL AND RAIL WEAR

• Theory and practice of management in terms of wheel and rail contact during the past 20 years are to increase the life of wheel and track and improve their adaptability and the use of greater axial loads. Effects of Friction Coefficient • The coefficient of friction depends on factors such as the microstructure of materials, load, quality levels and how it is the measured. Effects of Adhesion Coefficient• Adhesion or adhesion coefficient is defined as the maximum tensile strength in the wheel rim to the vertical load of the wheel and is defined in the contact area at the slip moment

steady state curving behavior

Reporter: Xavier Dei Retorta

How does Vehicle Behave Around Curves?

• Horizontal curves are provided when a change in the direction of the track is required and vertical curves are provided at points where two gradients meet or where a gradient meets the ground

• To provide a comfortable ride on a horizontal curve, the level of the outer rail is raised above the level of the inner rail. This is known as Superelevation.

Are u bored?

superelevation

• Also known as Cant

• It is the difference In height between the outer and the inner rail on a curve
• Provided by gradually lifting the outer rail above the level of inner rail
• The inner rail, a.k.a gradient rail, is taken as the reference rail and is normally maintained at its original level

superelevation

The followings are the main function of superelevation:

• To ensure a better distribution of loads on both rails

• To reduce the wear and tear of the rails and rolling stock
• To neutralize the effect of lateral force
• To provide comfort to passengers

equilibrium speed

• When the speed of a vehicle negotiating a curved track is such that the resultant force of the weight of the vehicle and of radial acceleration is perpendicular to the plane of the rails, the vehicle is not subjected to any unbalanced radial acceleration and is said to be in equilibrium.

• It is the speed at which the effect of the centrifugal force is completely balanced by the cant provided.

Maximum Permissible Speed

• This is the highest speed permitted to a train on a curve taking into consideration the radius of curvature, actual cant, cant deficiency, cant excess, and the length of transition.

Types of Cant

Cant deficiency (Cd)

• Occurs when a train travels around a curve at a speed higher than the equilibrium speed.
• It is the difference between the theoretical cant required for such high speeds and the actual cant provided.

Cant excess (Ce)

• Occurs when a train travels around a curve at a speed lower than the equilibrium speed.
• It is the difference between the actual cant provided and the theoretical cant required for such a low speed.

Types of Cant

Centrifugal Force on Curved Track

• A vehicle has a tendency to travel in a straight direction, which is tangential to the curve, even when it moves on a circular curve.
• This radial acceleration produces a centrifugal force which acts in a radial direction away from the centre
• To counteract the effect of the centrifugal force, the outer rail of the curve is elevated with respect to the inner rail by an amount equal to the superelevation
• A state of equilibrium is reached when both the wheels exert equal pressure on the rails and the superelevation is enough to bring the resultant of the centrifugal force and the force exerted by the weight of the vehicle at right angles to the plane of the top surface of the rails.
• In this state of equilibrium, the difference in the heights of the outer and inner rails of the curve is known as equilibrium superelevation.

curving behavior

Reporter: Xavier Dei Retorta

Curving Behavior

• A railway wheelset consists of two wheel rigidly connected by a single axle.

• Consequently, the outer wheel has a larger rolling radius (RL) than the inner wheel (RR), allowing it to traverse the longer path around the outer rail.

Curve Behavior

• In practice, the wheelsets are located within a frame, either a bogie or directly in the vehicle, and are restrained by a large yaw stiffness.

• If two wheelsets are mounted in rigid bogie, as shown in the picture, the axles are constrained to remain parallel to each other and so they cannot both align with the curve radius.

• The result is a high angle of attack between the wheel and rail in sharp curves, causing high flange forces, wear and increased risk of derailment due to flange climb.

Curve Behavior

• In practice, the yaw stiffness of the wheelset within the bogie is optimized to achieve good stability, while retaining suitable curving performance, by allowing the wheelset to align with the curve to some extent.

• The attitude of a bogie in a curve depends on many factors, but particularly the train speed, the curve radius, the wheel and rail transverse profiles and the cant (or inclination) of the track.

Curve Behavior

• As the leading wheelset has a high angle of attack (yaw angle of the wheelset relative to the rail) this wheelset tries to roll straight ahead but instead is constrained to roll around the curve by the flange.

Curve Behavior

• Typical force magnitudes acting on the four wheels of a bogie are shown schematically in the picture below

Curve Behavior

• The wheel/rail contact point on the leading inner wheel of a bogie is located towards the field side of the tread. This wheel experiences a high lateral creepage, as shown in the picture. The leading outer wheel is in flange contact, with the resultant horizontal force acting inwards to ensure that the wheelset remains on the track.

thanks!