The Shock Caused by Collision on Railway Vehicles Equipped

with Central Coupling

TĂNĂSOIU AURELIA, COPACI ION Departement of Engineering “Aurel Vlaicu” University

Arad, Calea Aurel Vlaicu, nr. ROMÂNIA

aurelia.tanasoiu@gmail.com

Abstract:The two transport systems, the conventional one characterized by the wheel-rail system and the magnetic levitation system have, as a fundamental distinctive factor, the method of obtaining sustentation, traction and propulsion of vehicles on the railway, including the necessary and fundamentally mandatory guidance. Each of the two traction systems has advantages and disadvantages. The paper aims to analyze and compare these two systems, from the point of view of infrastructure of the vehicles, guidance safety and travel dynamics as technical aspects, together with the economical implications which can also decide the optimal system to adopt. Keywords: shock caused by collision, shock insulators, stored potential deformation energy.

1. Introduction The shock load for railway vehicles is due

to the appearance of a relative velocity between neighbouring vehicles, both in travel as well as during the formation of freight trains.

The effect of the shocks, as loads appearing in use, is the transmission of forces through the central coupling of the vehicles and implicitly of accelerations to the masses of the vehicles, particularly to the transported freight and passengers.

In order to diminish the effects caused by the shock, railway vehicles are equipped with shock insulators (dampeners) that have the purpose of reducing the levels of the transmitted forces and accelerations.

The storage capacity for potential deformation energy of the shock insulators is

described by the β2

Ep

We factor (We –potential

deformation energy of the shock insulators; Ep – potential deformation energy of the vehicles) that determines the decrease of the level of forces and accelerations transmitted during the collision.

In the use of railway vehicles there is a tendency to increase travel speeds, reduce formation times for trains as well as increasing the axle load. Consequently, the forces and

accelerations transmitted to the vehicles as a result of the collision, reach relatively high values that need to be considered during the conceptionm design and execution of railway vehicles.

2. Dynamic Characteristics

Initially, the characteristic dynamic diagrams were obtained for the action of a shock caused by the free fall of a weight (ram), with a well determined mass, from different launching heights, on the buffer or central coupling dampener, affixed to a rigid plate [2].

The system thus adopted for testing differs significantly from the mechanical system encountered in the use of railway vehicles, specifically that formed by the masses of the two vehicles separated by the shock insulators, system which has a longitudinal freedom of motion.

The excitation function (system input), meaning the momentum "mv" of the ram mass is applied, through the buffer or central coupling dampener, to a plate of theoretically infinite mass. Thus, time variations are obtained for the force and contraction of the buffer or central coupling dampener, as response functions to the applied excitation, particular to the mechanical

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ISSN: 1790-5117 19 ISBN: 978-960-474-185-4

system used and different from those of the real system.

Consequently, through this method, characteristic dynamic diagrams are obtained that can not lead to a correct qualitative appreciation of the shock insulator, resulting in erroneous dynamic characteristics.

Through the process of experimentally determining the characteristic dynamic diagrams with the method of the falling ram, we have established the diagram in figure 1 for a central coupling dampener type S-2V-90, used by the railway administrations of the former USSR countries. In figure 2 we have presented the characteristic dynamic diagram of the same type of dampener, determined through the method of collision of two railway cars, each with a mass of ≈ 92t, at a collision velocity of 6,0km/h. The following observations can be made:

- The variation of force as a function of contraction differs significantly between the two. In the case of the diagram in figure 1, sudden increases of the force appear, followed by decreases. In the case of the diagram in figure 2, the evolution of the force is approximately linear up to a contraction of ≈ 75mm;

- The stored potential deformation energy and the dissipation coefficient η for the same maximum contraction Dmax=85mm have higher values for the collision, We=30,4KJ, η=0,88, than in the case of the falling ram, when We=21,8KJ, η=0,63.

Thus, large differences are observed in regards to the obtained dynamic characteristics, fact which categorically imposes the option of determining the characteristic dynamic diagram for shock insulators by the method of collision.

Fig.1

Fig. 2

3. On The Shock Caused by Collision

A series of authors have tried to

theoretically establish mathematical expressions of the forces and accelerations transmitted to the vehicles during the collision process.

The general case of the collision of two railway cars is considered. The colliding car, with mass m1 and velocity v1, impacts a collided car, of mass m2 and velocity v2, with v1 > v2. The cars are equipped with shock insulators (buffers or central coupling dampeners).

In the collision process a part of the kinetic energy of the vehicles is transformed into potential deformation energy which is maximum at time t12 when the vehicles travel at the same velocity v12. The expression of the potential deformation energy Ep is:

21

21p mm

mmE

+= ( )

2

vv 221 − =

2

v

mm

mm 2

21

21

+ (1)

where: m1 – mass of the colliding car; m2 – mass of the collided car; v– relative velocity between vehicles (collision velocity). Figure 3 shows the time evolution of the kinematic parameters, acceleration a, velocity v and displacement x, of the colliding car 1and the collided car 2 during the shock caused by a collision at 12 km/h. The cars had masses of m1= m2= 80t. On the figure we have noticed the sum of contractions of the bumpers of the colliding and collided cars D1+D2=196 mm. Another noticeable element is the moment t12 at which the cars have the same velocity and the process of transforming kinetic energy into potential deformation energy stored in the shock insulators (bumpers) ended.

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Fig. 3 Time evolution of acceleration a 2(t) of

collided car 2, determined experimentally and of the derived parameters v1(t) , v2(t) , x1(t) and

x2(t) for collision C → C

The study of the time variation of the motion parameters of the vehicles, as response functions to the shock caused by collision, leads to the following observations: 1. At each moment "t" of the collision process which occurs on the time interval (0-t2), the contraction "D" of the shock insulators that equip the vehicles is:

∫ ∫−=−=t t

dttvdttvtxtxtD0 0

2121 )()()()()( (2)

2. At the time t12, when the vehicles have the common velocity v12 and the stored potential energy of the vehicles is maximum, the difference between the distances traveled by the vehicles represents the maximum contraction of the shock absorbers "Dmax" and, obviously the surface " S ", between the curves v1 and v2 [2]:

∫ ∫ =−=−=12 12

0 0

21122121max )()()()(t t

SdttvdttvtxtxD (3)

3. Experimentally it is observed that, at time t = t*12 , the accelerations transmitted to the vehicles cancel out. Consequently, the vehicles move on the time interval (t*12- t2), with constant velocities "v*1" and "v*2" respectively, while remaining in contact on the whole interval, while the space between the vehicles increases " D(t) " = x1(t) - x2(t). This phenomenon occurs due to the fact that at time t*12 the shock absorbers of the vehicles show another deformation (remanent contraction) which, on the interval (t*12 - t2) cancels out. Thus, the increase of the space between the vehicles at each moment of the time interval (t*12 - t2) is compensated by the recovery

of the contraction of the shock absorbers. At the moment t2, whih marks the ened of the collision process, the shock absorbers (bumpers, central coupling dampeners) return to the initial position, corresponding to the moment t = t1 = 0 (the start of the collision process). 4. The process of transforming stored potential energy into kinetic energy, triggered at t = t12, ends at t = t*12 , when the vehicles reach velocities v*1 and v*2 respectively. Consequently, the values of the maximum contraction "Dmax" and the surface "S" which represents the value of the maximum contraction are:

∫∫ −=−=

*12

12

*12

12

)()( 21max

t

t

t

t

SdttvdttvD (4)

The energy coefficient that characterizes the efficiency of shock insulators is 2β, meaning the ratio between the potential deformation energy stored by the shock insulators, We and the total potential energy, which includes the potential energy stored by the elastic elements that represent the bearing structures, the elastic elements that form the suspension of the vehicle, equipment and existing load (freight, passengers): 2 β = We / Ep (5) The theoretical expressions of the transmitted force established previously can be used only in the conditions of the vehicles being equipped with shock insulators that have a linear variation between force and contraction. Railway vehicles can be equipped with shock insulators whose elastic elements have a non-linear variation between force and contraction [2], [3]. In the case of the collision of two vehicles of the same type, with m1 = m2 = m, KC1 = KC2 = KC, p1 = p2 = p , iar β1 = β2 = β, the expression of the transmitted force becomes:

( )p

K2

2

m

2

vvF C21

max β−

= (6)

where: - p=f(v) is the plenitude coefficient and represents the ratio between the stored potential deformation energy and the product between the maximum transmitted force and the maximum contraction of the shock insulator; - Kc=f(v) is the conventional rigidity of the central coupling dampener and is the ratio between the maximum transmitted force and the maximum contraction of the shock insulator.

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ISSN: 1790-5117 21 ISBN: 978-960-474-185-4

4. Experimental Determinations

During testing, the colliding car, launched from the inclined plane of the testing stand, collided, at different velocities, the collided car situated at rest and unbraked on the plane section of the stand. The used cars were 4 axle freight cars, loaded with bulk goods (sand, gravel, broken rock etc.) up to a total mass of 92t/car. At each shock caused by the collision of the cars, during the collision process, the following parameters were determined experimentally: - collision velocity v; - forces transmitted through the buffers F(t); -contraction of the dampener on the collided car D(t). The forces transmitted through the central coupling were determined using an own solution represented in the set-up shown in figure 4 and the force transducer in figure 5.

Fig. 4 Own conception set-up (1-force

transducer, 2-affixing device, 3-coupling head, 4-coupling end)

Fig. 5. 3 Orthogonal direction force transducer (elastic element equippedwith electric resistive

transducers)

Collision tests were conducted with the vehicles equipped with shock insulators with friction elastic elements in two situations: 1. elastic element with maximum displacement 90mm (figure 6); 2. elastic element with maximum displacement 130mm (figure 7).

Fig. 6. Central coupling dampener type S-2V-90

(1 hull of the dampening device; 2 pressure cone; 3 friction key; 4 exterior spring; 5 interior

spring; 6 tightening screw; 7 affixing nut)

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Fig. 7 Characteristic dynamic diagram of the

type S2-V-90 dampener

Fig.8. type S-6-TO-4 central coupling dampener (1 body of the dampening device; 2 cover; 3,4 tightening cone – 2 variants; 5 friction key; 6 tightening washer; 7 exterior spring; 8 interior

spring; 9 washer; 10 tightening screw; 11 affixer; 12 affixing nut)

Fig. 9 Characteristic dynamic diagram of the

no.1 dampener type S-6-TO-4-120 Figures 7 and 9 show the dynamic characteristics of the two shock insulators, determined experimentally at collision velocities that led to the reaching of the maximum contraction.

In figures 10 and 11 we have represented the variations as a function of velocity of the transmitted force and accelerations, respectively, for the collision at different velocities (F1, a1 – dampener with 90 mm displacement; F2, a2 – dampener with 130 mm displacement).

Fig. 10 Diagram of the force F transmitted

during collision as a function of the collision velocity

Fig. 11 Diagram of the transmitted accelerations

during collision, as a function of collision velocity

5. Conclusions

From the analysis of the experimental results, it is obvious that the different capacity for storing potential deformation energy of the two types of shock insulators that equipped, in turn, the railway vehicle during testing, determined the consequences reflected in figures 12 and 11. A considerable decrease of the forces and accelerations transmitted during the shock caused by collision is observed when comparing the presented situations 1 and 2

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. REFERENCES

[1]Copaci I., Trif E. ş.a. - Aplicarea metodei

tensometrice pentru calcularea forŃei

transmise şi a lucrului mecanic înmagazinat

de amortizoarele de şoc în timpul

tamponării. Revista Transporturilor şi TelecomunicaŃiilor nr. 3 la al II-lea Simpozion NaŃional de Tensometrie cu participare internaŃională, Cluj Napoca – 1980, pag. 33-39; [2] Sebeşan I., Copaci I. - Teoria sistemelor

elastice la vehiculele feroviare, Editura Matrix Rom BucureŃti – 2008; [3] Tănăsoiu Aurelia, Copaci Ion - Study on

the Sock caused by Collision of Railway

Vehicles, International Journal of Mechanics, ISSN 1998-4448, pag. 67-76, www.naun.org/journals/mechanics. [4] Aurelia Tanasoiu, Ion Copaci – Study on

the evolution of kinematic parameters

during the shock caused by railway vehicle

collision, Simpozionul InternaŃional “INTERPARTNER”22-27 sept. 2008, Alusta, Crimea.

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ISSN: 1790-5117 24 ISBN: 978-960-474-185-4