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An Investigation of a Locomotive Structural Crashworthiness Using Finite Element Simulation.


India is a developing country with the second largest population of 1.27 billion people. Indian economy is expected to grow at 5-8% gross domestic product (GDP) in the next decade. This growth in the economy will result in further expansion of metros and Tier 2 cities [1]. Indian Railways (IR) is the fourth largest railway network in terms of track, passengers, and cargo volume handling. IR will have to cater the increasing demands of passengers for faster and safe travel. High-speed trains are required to meet this purpose. Therefore, IR is focusing on developing new high-speed tracks and upgrading the existing infrastructure to exploit its higher speed limits, that is, from the existing 130-160 km/hr to 200 km/hr on major routes [2, 3, 4, 5, 6]. Hence to achieve this, IR has to attain service quality of international standards, considering safety parameters as indispensable. Crashworthiness, which is the structural ability of a vehicle to protect the passengers and drivers during an impact, is considered to be the important parameter at high speed [7, 8, 9, 10].

Crashworthiness is evaluated either predictively using finite element models and experiments or reflectively by breaking down crash results. Different criteria are utilized to evaluate crashworthiness, including the acceleration response and deformation patterns of the vehicle structure [11, 12, 13]. For the analysis, four scenarios are taken into account out of which two are associated with the collision of rail equipment with each other and the other two are related to the collision of the train to road vehicles. Practical tests using full-scale model and computer simulations are performed to study the effects of the collision on rail vehicles [14, 15, 16, 17]. The collision performance of rail vehicle is usually conducted with symmetric rigid objects. The Technical Specification for Interoperability (TSI) is a standard procedure where collisions with rigid objects are conducted to evaluate the crashworthiness of rail vehicle [19]. Computer simulation is the preferred method to test the crashworthiness as compared to the practical method of testing which not only is an expensive procedure but also consumes a lot of time.

Finite element analysis (FEA) and multibody dynamics methods are currently utilized to examine rail vehicle collisions, crashworthiness, and deformations of energy-absorbing elements. Multibody dynamics is used to study the complete movement of a whole train, whereas finite element modeling is performed to obtain refined outcomes [18, 19, 20, 21]. The FEA is a numerical method which breaks down the continuous system to discrete systems which are called elements. FEA is a powerful method of solving challenging engineering problems because it permits applying boundary conditions to make an accurate model which allows the study of collision impacts. Explicit FEA is used to simulate collision of rail vehicles as the time frame of such events is very small. It involves nonlinear behavior and deformations that occur commonly in a collision scenario.

IR presently uses electric and diesel locomotives. For electrical passenger locomotive, Wide gauge Alternating current for Passenger (WAP) series, that is, WAP-1, WAP-4, WAP-5, and WAP-7, etc., is used which run through 25 kV AC system with overhead lines. In this article, the analysis is mainly focused on the modification of the WAP-5 locomotive design. Therefore, it is essential to examine the locomotive crash behavior during the impact test. In this FEA, the crashworthiness of a locomotive is assessed by impacting it on a rigid wall at various speeds, that is, 25 km/hr, 100 km/hr, 160 km/hr, and 225 km/hr.

Finite Element Model for Locomotive

Description of Locomotive

WAP-5 is a dual-cab forward-type high-speed IR electric locomotive. It was initially imported from ASEA Brown Boveri, Switzerland, but is now manufactured by Chittaranjan Locomotive Works, India. It has a peak power output of 4500 kW and includes regenerative braking as one of its eminent characteristics. The other main features are flexible gear coupling, wheel-mounted disc brakes, pantry loads, and an ability to attain higher speed up to 225 km/hr.

Braking system includes 160 kN regenerative brakes, automatic train air brakes, locomotive disc brakes, and a parking brake. It is the fastest locomotive of IR and runs at 160 km/hr.

Figures 1 and 2 show the geometrical diagram and a side view of WAP-5 locomotive, respectively. Salient features of WAP-5 are listed in Table 1.

Finite Element Model

The FE techniques have been thoroughly utilized in simulating diverse dynamic problems through the discretization of the whole structure into finite elements. Implicit and explicit methods are used to solve the FEA. For crash simulation events which have a nonlinear transient dynamic problem and have very short duration of time, an explicit method is the most suitable one [8]. The locomotive and its rigid wall have been modeled using solid works; meshing is done in hyper works and imported to ANSYS for explicit analysis (Figure 3).

The FE model is based on an actual representation of the locomotive front structure which had a fine mesh and treated as a deformable component. Different sections of the locomotive are simplified and considered as rigid bodies except the extreme modules (Appendix A). Skin plates are neglected in the modeling. The complete locomotive is generated including substructures such as pushback couplers and buffers.

The coupler with draft gear works according to the force-stroke characteristics [12]. Buffers absorb a large amount of the impact energy during the crash. However, the body front structure is also subjected to the impact as the buffers are mounted to the frame. Computer-aided design (CAD) model is based on solid elements. The actual front structure is generally made of a large number of steel elements in the form of sheet metal plates and sections welded together; therefore, it is modeled with shell finite elements. The transformation from solid objects (CAD model) to the surface model (FEM) required applying of the midsurface procedure (Figure 4). Midsurface is generated between two sidewalk of the solid exactly at the mid of them.

The configuration of the frame is very complex (fillets, sections, etc.) and automatic meshing is utilized. The FE mesh of the frontal locomotive is gradually refined toward the impacting end of the model to exactly determine the deformation of the structure in a collision, with a characteristic element length of 15 mm. The mesh is relatively regular and it consists of both rectangular and triangular elements. The anti-climbers have a characteristic element length of 0.5 mm. These models are formulated to determine their crushing and vertical strength. Large deformation is anticipated in the locomotive frontal area and it has an element size of approximately 5 mm. The element size increases to 25 mm for the remaining part and increases progressively toward the rear of the locomotive.

The front structure is considered as a deformable component and *MAT_PLASTIC_KINEMATIC is applied to the whole frame elements. This model is suitable for incorporating isotropic and kinematic hardening plasticity. Table 2 gives the material properties of WAP-5. Complete FE model (Figure 5) consists of 150,367 finite elements and 249,285 nodes. 98,950 deformable shell elements are used to simulate the frame and buffers, whereas 21,586 solid elements are used to simulate other components as rigid bodies. 28 beam elements are used to represent springs and dampers. In addition, 40-lumped masses are attached to the model to ensure its correct mass. Meshing details are provided in Table 3.

The locomotive frame consists of over 94 thousands of grouped elements in nine parts, and each part is described by the different thickness of the shell element (Appendix A). As the sum of different masses considered in the model represents the total mass of the designed locomotive (about 11 tons), the density of some components is modified and few lumped parameters are added in the model to ensure its proper mass.

A mesh quality is checked through orthogonal and skewness quality and mesh metric is given in Table 4. The element percentage lie in different quality zone is given in Table 5. It can be seen that the major percentage of elements lie in very good zone and very few percentage of elements fall in unacceptable zone. Therefore, the mesh quality has passed the orthogonal and skewness quality test.

Validation of Crashworthiness

The FE model is validated in terms of acceleration and energy balance by experimental result obtained by the Research Designs and Standards Organisation (RDSO) and European Standard (EN) 15227 [22]. The head-on collision analysis with the identical unit is considered and locomotive is impacted on a rigid wall at the speed of 25 km/hr. Since the rigid wall does not absorb any energy, it results in a condition of a head-on collision of two trains and satisfies the first condition as per EN 15227.

The simulation results show that the frontal part of locomotive crashed and maximum deformation is about 2.01 m as shown in Figure 6.

Figure 7 shows the comparison of acceleration during collision. To determine the efficiency of the crash analysis, it is essential to evaluate the energy balance of the system. The energy balance estimate in the crash analysis is expressed in Equation 1:

[E.sub.I] + [E.sub.FD] + [E.sub.KE] - [E.sub.SW] + [E.sub.v] = [E.sub.TOT] Eq. (1)

Figure 8 indicates the total energy segment [E.sub.TOT], which have been determined from Equation 1, and few major energy components, that is, kinetic energy [E.sub.KE], internal energy [E.sub.I], and artificial strain energy, external work by mass scaling, and work done by the external loads during the collision analysis. If the total energy in the finite element model does not change, the total error is usually below 1%, which indicates that the crash analysis results have been validated. It is obvious that kinetic energy converts into internal strain energy in the course of simulation. As per ECE R66 norms, the amount of nonphysical energy components must be within 5% of the total energy. The artificial strain energy, which consists of the stored energy in the hourglass resistances and transverse shear in the shell elements, is negligible as compared to the total energy which is in the acceptable range. The values of acceleration are in the ranges as per experimental result. There is a good matching among the experimental and simulated results.

Results and Discussion

Simulation Scenario

The simulation scenario of a locomotive impacting on a rigid wall (Figure 5) is a general representative scenario of crash simulation. Three scenarios are taken into consideration with the initial speed of 100 km/hr (average speed), 160 km/hr (maximum running speed), and 225 km/hr (design speed) [22, 231. The simulation is performed for 0.4 s, which is sufficient to record the collision response. A controlled gradual collapse of the frontal structure is crucial for locomotive crash-worthiness design to absorb energy [24, 25, 26, 27, 28, 29, 30]. To display the deformation clearly, the second half of the locomotive is neglected. Initially, the front side sill, absorber, and front underframe have impacted with the rigid wall and collapsed, absorbing most of the total energy (Figure 9); then, the cab begins to deform and absorbs the remaining energy.

For the speed of 100 km/hr and 160 km/hr, the maximum deformation is 4.07 m and 6.05 m, respectively, and the front cabin of the locomotive is crashed completely. The deformation sequence of the front-end structure of a locomotive during the crash (160 km/hr) is described in Figure 10. The force history curves for the collision are described in Figure 11.

The first event depicts energy absorbed by the front coupler, after which the second event depicts forces occurring at collision energy-absorbed devices. Impact force is having high values of thrust on the underframe and the upper frames, which progressively increased. Collision energy absorption scenarios for frontal crashworthiness of the locomotive are developed corresponding to the design intent and at the speed of 225 km/hr; the maximum deformation is 8.22 m (Figure 12).

During this impact, the locomotive is crashed approximately to half of its length. The front cabin and middle section of locomotive are deformed completely. It is noticed that local buckling occurs at different points, which reduces the desired progressive damage behavior.

Reference node displacement (RND) in the longitudinal direction is given in Table 6. Figure 13 shows the RND in the longitudinal direction. The difference in the curve is for RND of the central area to the right and left sides of the locomotive, expressing the deformation of the central area to the right side of the locomotive and central area to the left side of the locomotive, respectively. It exhibits small rigid movement in the last stage, in which the right side moves forward and the left side retreats.


In this article, the main focus is on modernization of the WAP-5 locomotive. Therefore, it is required to determine the locomotive crash behavior during the impact test. The crashworthiness of a locomotive is carried out through the FE A by impacting it on a rigid wall to evaluate its maximum deformation at higher speed. FE model of the locomotive includes some simplifications due to high complexity of the actual object. The proposed FE model used in the dynamic numerical analysis is the only possibility since the experimental test on the complete locomotive is impractical and impossible at the moment. The FE model is validated at the speed of 25 km/hr in terms of acceleration and energy balance by experimental result and EN 15227. Longitudinal deceleration for the locomotive does not exceed the permissible values.

The buffers are fully compressed immediately after impacting with the wall and, therefore, are not able to absorb the energy. Thus, the energy must be absorbed by the frame that may lead to excessive strains and permanent plastic deformations. The results provide qualitative and quantitative data associated with the locomotive crash behavior during the collision. It may be useful for the designer in further modernization of the locomotive structure. This is the simplest and the most ideal crash scenario, but it is very useful to obtain general characteristics of the crash behavior of the locomotive. In the future, the crash study of two locomotives can be performed on the basis of the models presented.


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Appendix A: Detailed Summary of the FE Model

Part ID  Part name          Element type  Number of elements

 1       Buffers            Shell             2506
 2       Frame_floor        Shell             1537
 3       Frame 18           Shell          141,239
 4       Frame 14           Shell             6425
 5       Frame 16           Shell           16,853
 6       Frame 11           Shell           17,521
 7       Frame 12           Shell             8320
 8       Frame 13           Shell             3648
 9       Frame 15           Shell           11,716
10       Frame 17           Shell              198
11       Connectors         Shell              530
12       Buffer spring      Beam                 5
13       Reservoir 11       Solid              140
14       Reservoir 22       Solid              374
15       Reservoir 33       Solid              250
16       Generator module   Solid               83
17       Storage module     Solid               98
18       Cab                Solid              198
19       Electric module    Solid               78
20       Pneumatic module   Solid               52
21       Compressor module  Solid              234
22       Other              Solid           37,281
                            Total          249,285

Part ID  Material type                    Thickness (shell only) (mm)

 1       Plastic kinematic                25.0
 2       Plastic kinematic                 5.0
 3       Plastic kinematic                 5.0
 4       Plastic kinematic                15.0
 5       Plastic kinematic                10.0
 6       Plastic kinematic                 9.0
 7       Plastic kinematic                 7.6
 8       Plastic kinematic                 6.0
 9       Plastic kinematic                20.0
10       Plastic kinematic                18.0
11       Plastic kinematic                 8.0
12       Nonlinear elastic discrete beam
13       Rigid
14       Rigid
15       Rigid
16       Rigid
17       Rigid
18       Rigid
19       Rigid
20       Elastic
21       Elastic
22       Rigid

Sunil Kumar Sharma, Amity School of Engineering and Technology, Amity University Uttar Pradesh, Noida, India

Rakesh Chandmal Sharma, Maharishi Markandeshwar (Deemed to be University) Muliana, India


Received: 28 Nov 2017

Revised: 05 Jul 2018

Accepted: 30 Jul 2018

e-Available: 02 Nov 2018

TABLE 1 Salient features of WAP-5 [23].

Feature                   WAP-5

Manufacturer              Chittaranjan Locomotive Works,
                          West Bengal, India
Traction motor            ABB's 6FXA 7059 three-phase
                          squirrel cage induction motors
                          (Torque 6930/10000 Nm, 1150 kW,
                              96% efficiency, 1583/3147 rpm)
Train ratio                   67:35:17 (three-stage gears)
Axle load (tons)              19.5
Power                     Maximum: 4500 kW
Tractive effort           Maximum: 258 kN
Diameter of wheel           1092 mm (new), 1016 mm (full worm)
Wheelbase                 13,000 mm
Bogies                    Bo-Bo, Henschel Flexi float
Body width                     3.144 m
Locomotive weight (tons)      78
Cab length                  2434 mm
Pantograph locked down      5437 mm

TABLE 2 Material property of WAP-5.

Description            IS-2062
Modulus of elasticity  210 GPa
Tangent modulus          1 GPa
Poisson's ratio          0.3
Density                  7.85E-09 ton/cubic mm
Yield stress             0.6 GPa
Yield stress           250 MPa
Ultimate stress        490 MPa

TABLE 3 Meshing details of locomotive.

Number of nodes    249,285
Number of element  150,367
Shell               98,950
Solid               21,586
Beam                    28

TABLE 4 Mesh quality testing.

Mesh metric         Orthogonal quality  Skewness quality

Min                 0.01                1.31E-10
Max                 1.00                1.00
Average             0.89                0.21
Standard deviation  0.20                0.24

TABLE 5 Percentage elements and quality zones.

S. No.  Quality zone  Orthogonal (%)  Skewness (%)

1       Very good     69.23           78
2       Good          27.12           12
3       Acceptable     3.65            9
4       Unacceptable   0               1

TABLE 6 RND in the longitudinal direction.

               RND of right side  RND of left side  RND of central area
Speed (km/hr)  locomotive         locomotive        locomotive

 25            110,542            111,398           1659
160            112,542            110,398           2756
200             91,542             91,998           3253
225            121,642            121,198           4445

               Crash zone collapses  Deformation at central
Speed (km/hr)  (ms)                  area (ms)

 25            297                   309
160            199                   207
200            166                   175
225            134                   142
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Author:Sharma, Sunil Kumar; Sharma, Rakesh Chandmal
Publication:SAE International Journal of Commercial Vehicles
Article Type:Report
Date:Oct 1, 2018
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