HARDNESS INDICES ESTIMATION OF SUPPORTING STRUCTURE ELEMENTS OF MOTOR BOGIES OF THE ELECTRIC TRAIN ED9M

Dep. «Structural Mechanics», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipropetrovsk, Ukraine, 49010, tel./fax +38 (056) 793 19 08, e-mail onildpps@gmail.com Dep. «Structural Mechanics», Dnipropetrovsk National University of Railway Transport named after Academician V. Lazaryan, Lazaryan St., 2, Dnipropetrovsk, Ukraine, 49010, tel./fax +38 (056) 793 19 08, e-mail onildpps@gmail.com The State Administration of Railway Transport of Ukraine, Tverska St., 5, Kyiv, Ukraine, 03680


Introduction
In 2007 Russia bought a certain amount of electric trains ED9M produced by the Demikhiv plant of mechanical engineering in relation to the need to meet the demands for suburban passenger transportations and for the renewal of electric train fleet in Ukraine [6].
Fig. 1, 2 show a general view of the head and motor cars of this electric train, when Fig. 3, 4 shows the general view of the motor car bogie and the central suspension beam [10,11].As it was found out in a short operation period of these electric trains on the AC powered stations with quite simple profile in terms of loading, a beam fracture incident of the central suspension for electric train bogie had occurred.Fig. 5 shows a view of such beam.

Fig. 5. General view of the fractured beam
It is known that fractures occur in the places of maximum loadings, arising during operation.At the same time it should be noted that crack appearing, its development and fracture is to a great extent caused by the presence of excessive concentrators in the corresponding place due to poor casting.
A lot of works are dedicated to the following issues: the dynamic loading determination, comparative evaluation of various techniques during research conducting to identify the fatigue indicators and the resource of the bogie supporting structures, bench development and conduction of vibration bench testing for fatigue failure.These works were published in Ukraine and Russia [1,3,4,7] and in the foreign countries as well [2,12,13].

Purpose
Aim of the study was to find out the factors that could lead to the fracture of the central suspension beam and on the basis of relevant work to develop a set of measures to improve the durability performance.

Methodology
To assess the stress levels that can be created in both the central suspension beam and in the basic bearing structures of the bogie frame a solid model displaying the configuration and the design features were created [14] and the finite-element calculation model was developed [9].
Beam models and the bogie frames are shown in Fig. 6 and 8 and its finite element calculation model -in Fig. 7 and 9.The finite-element model of the bogie frame consists of 65144 elements and 131172 junctions.
According to the developed finite-element schemes [9] the calculations with the following operation modes modeling were carried out: 1. Determination of static stress elements from the body weight action.It is assumed that the motor car body weight 64.9 tons is evenly distributed among all the bearings and thus 32.45 tons fall to each central suspension beam.Then this loading is transferred to the bogie frame longitudinal beams; 2. Determination of the maximal stress levels during the coasting motion of electric train.In this case, it is assumed that the static loading from the body is increased by (1 + C VD ) time, where C VD is the coefficient of vertical dynamics of central suspension; 3. Determination of the maximal stress levels during motion in traction mode.In this case, the horizontal lateral N and traction F T forces in the connection junctions of shifter arm, as well as bending moments in the vertical М v and in the horizontal М h areas are applied to the central suspension beam and longitudinal beams of the bogie frame.

Findings
Using the developed models [14] and finiteelement schemes [9] the impact assess of geometric design parameters of the spring sets bearings, which are attached to the profile base of the beam on the stress state of these elements was calculated.
Figure 10 shows the distribution field of stresses in case the strengthening ribs of the spring set bearings, connecting with the profile base of the central suspension beam are absent.Table 1 shows the levels of maximal stresses in the most loaded areas of the central suspension beam in the proposed options of modernization for the supporting junction of spring set.
For the steel 09 H2S, which is used to product the supporting structures for rolling stock, the value of strength limit is 500 MPa, and liquid limit is 359 MPa.

Originality and Practical Value
On the basis of the worked out models and conducted research the scientifically grounded measures of modernization for central suspension beams of the electric cars ED9M were developed.It was obtained that the design of spring set support with the strengthening ribs 25 mm thick and the roundings of 15 mm radius along the height is the best one.As a result of the research it was developed an engineering solution of measures to improve the strength performance of the central suspension beams for the motor cars of electric trains ED9M.This solution was transferred to the specialists of Ukrzaliznytsya to implement them during the PR3 or overall repairs.

Conclusions
The results of calculations and the obtained fields of stress distribution in the central suspension beam showed that the fracture occurred in the areas of maximal stresses, which are created in the operation condtions.The crack appearing, its development and fracture is also caused by the presence of excessive concentrators due to the poor casting.
On the basis of obtained results of theoretical studies it was found out that the junction of spring set support with strengthening ribs 25 mm thick and with roundings of 15 mm radius along the height is the best one.
General view of the best modernization variant, which has minimal stress levels and meets the requirements to the strength parameters [5] is shown in Fig. 14.
For bogie frame in the most unfavorable loading mode (calculation example of which is shown in Fig. 13) it was found out that the greatest stress levels on the top sheets of longitudinal beams reach 100 MPa.In the middle of the longitudinal beams between the junctions of vertical loading transmition the maximal stresses are changing in the range of 56-70 MPa.On the transverse beams in the places of their junction to the longitudinal beams the maximal stresses are 40 MPa and 30 MPa in the middle.

Fig. 14. General view of the best modernization variant of the central suspension beam
On the bottom sheets of longitudinal beams in the area of load transferring from the bogie weight and central suspension beam the maximal stresses reach 126 MPa.
In the junction of transverse beams to the longitudinal beams the maximal stresses do not exceed 30 MPa, including the locations of support brackets for traction gear boxes.
On the basis of strength calculations of the basic supporting structures for motor bogie frames it can be concluded that the above mentioned stresses are those, which do not constitute a threat to the strength safety of their state [5].But during operation of the electric trains ED9M in the motor bogies the condition of the longitudinal beams in the places the transmit nodes of vertical loading from the body and the bolster to the bogie frame should be controlled.

Fig. 1 .
Fig. 1.The head car of the electric train ЕD9М

Fig. 10 .
Fig. 10.Stress distribution field under static loading and absence of strengthening ribs Fig. 11 shows the results of the stress-strain state calculation from the effect of static loading in case the strengthening ribs have the same thickness as in the fractured beam of central suspension.

Fig. 11 .
Fig. 11.Stress distribution field under static loading with small strengthening rib

Fig. 12
Fig.12shows the results of calculation of the stress-strain state during motion in traction mode for the case when the strengthening ribs have the same thickness as in the fractured beam of central suspension.

Fig. 12 .
Fig. 12. Stress distribution field during motion of electric train in traction mode with small strengthening rib Fig. 13 shows an example of the stress distribution field of the motor bogie frame during the modeling of motion; where in addition to the loading from body weight the force of buff dynamic loading in the fusing unit of traction gear box to the bogie frame is taken into account.

Fig. 13 .
Fig. 13.Stress distribution field in the mode of motion, where the buff dynamic loading from the forces in the fusing unit of traction gear box to the bogie frame.