- Email: [email protected]
Life extension approach focusing on industrial and railway applications
ScienceDirect
Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2019) 000–000
ScienceDirect
www.elsevier.com/locate/procedia
Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2019) 000–000
ScienceDirect
www.elsevier.com/locate/procedia
Procedia Structural Integrity 19 (2019) 665–673
Fatigue Design 2019
Life extension approach focusing on industrial and railway Fatigue Design 2019 applications Life extension approach focusing on industrial and railway Anne Coulona, Julien Fondrata,Nicolas Vincenta, Philippe Négrierb*, Jean-C. Renardb* applications VibraTec, 28 chemin du petit bois, 69131 Ecully, France a Lyon Cedex 03, France b Sytral, 21bda Vivier Merle, CS63815, 69487 a
Anne Coulon , Julien Fondrat ,Nicolas Vincent , Philippe Négrier *, Jean-C. Renardb* a
Abstract
b
a VibraTec, 28 chemin du petit bois, 69131 Ecully, France Sytral, 21bd Vivier Merle, CS63815, 69487 Lyon Cedex 03, France
b
Using its expertise in fatigue analysis, VibraTec has developed an approach to evaluate remaining life aiming to ensure asset durability and optimize operation to extend service life. Remaining life provides visibility of the structure’s future life to anticipate Abstract difficulties and guarantee long-term quality of service. Analysis of this parameter is an important part of asset management for structures designed to for decades, railwayhas transportation. Using its expertise in last fatigue analysis,like VibraTec developed an approach to evaluate remaining life aiming to ensure asset durability and optimize operation to extend service life. Remaining life provides visibility of the structure’s future life to anticipate The approach forlong-term evaluatingquality remaining life is based on aofcoupled digital and experimental fatigue analysis. The difficulties andpresented guarantee of service. Analysis this parameter is an important part of asset management for sensitive areas of thetostructure under study firstlytransportation. determined by Finite Element Analysis according to nominal fatigue loads. structures designed last for decades, like are railway The current status of structural mechanical integrity is studied by concentrating nondestructive examinations on sensitive areas (NDT, magnetoscopy, observation, etc). Then, areand performed to identify theanalysis. real operational The approach presentedvisual for evaluating remaining life operational is based on ameasurements coupled digital experimental fatigue The loads, to evaluate andstructure tune the under Finite study Element Using final reliableAnalysis Finite Element Model, the future life of the sensitive areas of the areModel firstly (FEM). determined by the Finite Element according to nominal fatigue loads. structure is simulated. Different operation road maps can be evaluated to ensure structural durability and extend asset service The current status of structural mechanical integrity is studied by concentrating nondestructive examinations on sensitive areaslife. (NDT, magnetoscopy, visual observation, etc). Then, operational measurements are performed to identify the real operational To conclude the paper, the method is Element then applied to quantitatively thereliable remaining lifeElement car bodies for railway networks. loads, to evaluate and tune the Finite Model (FEM). Usingassess the final Finite Model, the future life of the Operationisand maintenance roadoperation maps serve as maps guidescan to reach service to lifeensure objectives. Structural modification can alsoservice be structure simulated. Different road be evaluated structural durability and extend asset life. evaluated to optimize life duration. This analysis provides support for investment teams, helping them optimize their asset management strategy. To conclude the paper, the method is then applied to quantitatively assess the remaining life car bodies for railway networks. Operation and maintenance road maps serve as guides to reach service life objectives. Structural modification can also be © 2019 The by Elsevier B.V. provides support for investment teams, helping them optimize their asset evaluated to Authors. optimize Published life duration. This analysis Peer-review under responsibility of the Fatigue Design 2019 Organizers. management strategy. © Published by Elsevier B.V. B.V. © 2019 2019The TheAuthors. Authors. Published by Elsevier Peer-review under responsibility of the Fatigue Design 2019 Organizers. Peer-review under responsibility of the Fatigue Design 2019 Organizers.
* Corresponding author. Tel.: +33 472 866 565. E-mail address: [email protected] 2452-3216 © 2019 author. The Authors. Published Elsevier B.V. * Corresponding Tel.: +33 472 866by565. Peer-review under responsibility of the Fatigue Design 2019 Organizers. E-mail address: [email protected] 2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers.
2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 10.1016/j.prostr.2019.12.072
Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Anne Coulon/ Structural Integrity Procedia 00 (2019) 000–000
666 2
Keywords: Remaining life, railway transportation, asset durability, extend service life, digital and experimental operational analysis.
1. Introduction Using its expertise in fatigue analysis, VibraTec has developed an approach to evaluate remaining life aiming to ensure asset durability and optimize operation to extend service life. Remaining life provides visibility of the structure’s future life to anticipate difficulties and guarantee long-term quality of service. Analysis of this parameter is an important part of asset management for structures designed to last for decades, like railway transportation. The approach is then applied to urban car bodies for railway transportation. Rolling stock maintenance, renovation and/or replacement costs are major issues for their owners. Indeed, remaining life studies are essential to make the right decisions in terms of sustainable development and investment for rolling stock owners. Nomenclature
Tnom Nominal life Fnom Nominal load Fact Actual load lim, nom Nominal strength limit lim, act Actual strength limit max, nom Maximal nominal stress Reference acceleration cycle range ref
i
Ni N eq
Test acceleration cycle range
Test number of acceleration cycles Equivalent test number of acceleration cycles
2. Methodology The development process of a new product can be synthetized using a V-Model as presented in Fig. 1. The remaining life methodology developed by VibraTec is based on the same process. Designer requirements Nominal life: Tnom Nominal load:
Acceptance testing Operating loads Actual load: Fact
Fnom
Design and production Design margin: max, nom ≤ lim, nom ? Quality of fabrication:
lim,
act
≤
lim,
nom
?
Fig. 1. Remaining life methodology presented in a product development V-Model
Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Coulon / Structural Integrity Procedia 00 (2019) 000–000
667 3
Determination of load margin coefficient C1: In the requirement analysis phase, the first step in the process, the requirements of the system are collected by analyzing the needs of the user(s). In a remaining life context, the product is operational and actual operational loads Fact are available by measurement in situ. In the V-Model, standard loads Fnom used in the initial development process of the product are updated by the actual loads of the product. The initial design is evaluated regarding the comparison of standard and actual loads. To evaluate the remaining life, the load margin coefficient corresponding to the ratio between nominal and actual loads, for the same number of cycles, is defined:
C1
Fnom Fact
(1)
Determination of design margin coefficient C2: Systems design is the phase where system engineers analyze and understand the business of the proposed system by studying the user requirements document. They figure out possibilities and techniques by which the user requirements can be implemented ensuring the structural mechanical behavior of the product. Many actual products and installations have been designed with old structural analyses, using less efficient FEA tools than current ones. An FE computation with the nominal load is performed. The initial design is criticized comparing the maximal computed stress to the nominal strength limit. The design margin coefficient is then determined thanks to the ratio between the nominal strength limit and the maximal computed stress on the whole structure under the nominal load:
C2
lim,
(2)
nom
max,
nom
Determination of production margin coefficient C3: Then, the structural mechanical integrity of the product is studied by nondestructive examination (NDT, magnetoscopy, visual observation, etc). Strength and quality of material and assembly (welded joints etc) are observed and quantified. The strength limit considered in the initial design is updated and criticized regarding the manufacturing quality. A third correction factor corresponding to the ratio between actual and nominal strength limits is defined to evaluate the remaining life:
C3
lim, lim,
(3)
act
nom
At this step and considering Basquin law, the overall life evaluation can be done using the formula:
Tact Tnom * C1b * C 2b * C3b Then the remaining life is given by:
(4)
Re mainingLif e Tact Age
The last step concerns the validation of the remaining life evaluation according to the potential appearance of cracks or failures on the actual fleet. The maintenance plan and the dated failure inventory must be analyzed since entry into service. This analysis must be completed by the nondestructive examination realized previously. Once the reliability of the remaining life evaluation is validated, operation road maps and maintenance plans for the future life are defined.
Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Anne Coulon/ Structural Integrity Procedia 00 (2019) 000–000
668 4
3. Case study: Car body This approach has been applied by VibraTec on different railway structures like bogies, car bodies, infrastructure components, etc. In this publication, the approach is presented on a concrete car body case. This analysis was done in collaboration with the Lyon transport organization authority Sytral on two rolling stocks: tramway CITADIS and metro MPL75, respectively 15 years old and 40 years old at the study time. Rolling stock maintenance, renovation and/or replacement costs are major issues for their owners. Indeed, remaining life studies are essential to make the right decisions in terms of sustainable development and investment for rolling stocks owners. As described previously, the approach presented for evaluating remaining life is based on a coupled digital and experimental fatigue analysis. First, the current status of car body’s structural mechanical integrity is studied to quantify the relevance of the manufacturing and the initial design. Then, operational measurements are performed to identify the real operational load, to evaluate and tune the FEM. Using the final reliable FEM, the future life of the structure is simulated. Finally, different operation road maps and modifications can be evaluated to ensure the structural durability and extend asset service life. 3.1. Current status The expertise of the car body’s mechanical integrity is based on complementary use of simulation and examination control. A FE model of the car body is built and then standard loads from EN 12 663 (2015) are applied, see §3.1.1. From this FE analysis, sensitive areas are determined and make it possible to focus the examination control on these areas, see §3.1.2. 3.1.1. FE Simulation The FE model is built from paper plans or 3D if available. The modelling approach is based on VibraTec experience. The mechanical structure is modelled, and non-structural elements (covering, equipment, etc) are considered as mass and inertia at center of gravity. The mesh size is defined to be fine enough to compute the stress in sensitive areas like welding areas. All the connections are modelled to represent the mechanical behavior. Mass balance of the model is updated using actual mass of the system. The modelling is done using NX 11 Siemens software and the computation is done with NX Nastran solver. FE models of MPL 75 and CITADIS are presented in Fig. 2. a
b
Fig. 2. (a) MPL75 FE model; (b) Citadis FE model.
Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Coulon / Structural Integrity Procedia 00 (2019) 000–000
669 5
As part of the sensitive area evaluation phase, loads are extracted from EN 12 663 standard. Loads applied to the car body are: o Vertical +/- 0.18g for CITADIS 0.15g for MPL75, o Lateral +/- 0.15g, o Longitudinal +/- 0.2g. To identify the sensitive areas, several computation configurations are studied for each excitation direction considering the most severe connection between bogies and car body. It is noted that EN 12 663 standard specifies a durability of 10 7 cycles for each load direction. Fatigue stress limits of sensitive areas such as weldings are defined according to Eurocode 3 (2014), Eurocode 9 (2014) and IIW (2016). According to the fatigue stress analyses for each load case (Fig. 3), the sensitive areas are determined considering the cumulated damage of each load case. Rivet and screw fatigue behavior are also studied regarding loads transiting in them. All sensitive areas are listed from FE fatigue analysis and then inspected by an expert, see §3.1.2. From these results, the initial design is also criticized comparing the maximal stress computed to the nominal strength limit. This analyze corresponds to the second correction factor of the remaining life evaluation, see §2. Theoretical Fatigue stress limit
Fig. 3. Stress map on CITADIS for vertical load.
3.1.2. Inspection Inspection of sensitive areas is done by an expert from the Institut de Soudure. Visual and nondestructive examinations are done in each sensitive area indicated on 3D, see Fig. 4. Potential cracks are detected (see Fig. 5.) and their criticality is evaluated regarding their propagative status. The strength limits considered in the initial design are updated and criticized regarding the manufacturing quality of welds and their current status in the sensitive areas (C3 coefficient).
Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Anne Coulon/ Structural Integrity Procedia 00 (2019) 000–000
670 6
Fig. 4. Some of sensitive areas to control on MPL75.
Non-compliant Fig. 5. Nondestructive examination.
3.2. Measurements under operating conditions Measurements are done for the different configurations identified during the initial computation (ex: rolling, loading/unloading of passengers, etc) and for situations representative of real service conditions. Sensitive areas defined in §3.1 are instrumented with strain gauges to identify stress cycles. In parallel, several triaxial accelerometers are also positioned on the car body to characterize its dynamic behavior and to register actual operational loads. For rolling measurements, the train speed and localization are also recorded. Comparing nominal loads of EN 12 663 standard and actual loads, the load margin coefficient can be determined. As nominal loads are defined in terms of acceleration cycles, the comparison is done on the effective number of cycles corresponding to the reference acceleration range ref . An equivalent damage analysis is done weighting each acceleration range count by equivalent damage of reference acceleration range using equation (5) from Basquin law:
N eq ref N i i i 0 ref n
The coefficient
b
C1b is then given by: C1b
(5)
10 7 N eq
Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Coulon / Structural Integrity Procedia 00 (2019) 000–000
671 7
Loads on the MPL75 car body are compared in specific operating conditions with empty and full loads to reference in Table 1. Regarding those results, the car body load is an important parameter. Number of cycles count for full load is more than 10 times higher than the empty load in the vertical direction. In full load extreme conditions during the whole car body life, the equivalent number of acceleration cycles is higher than the standard. The same work is done to compare standard to realistic operational loads, corresponding to a specific repartition between empty and full car body loads. These results are not presented here, but enable an evaluation of the initial design. Table 1. Comparison of equivalent and reference number of acceleration cycles on MPL75. Test Direction
Full load
Standard
Empty load
Reference load
Lateral
9.9 104
3.1 105
1 107
Vertical
7.4 10
5.8 10
1 107
7
6
From strain gauge and GPS measurements, stresses are projected on the network, see Fig. 6. This visualization makes it possible to correlate the stress events and the network localization and specificity (rail default, specific curve, etc). Each line is characterized in terms of damage to the car body. The stress events are also compared to the car body dynamic behavior from accelerometers. Finally, measurement analysis makes it possible to correlate the fatigue behavior, the network and the car body dynamic behavior. From this analysis, network operations can be adapted to reduce the car body fatigue damage.
Fig. 6. Stress map on tramway line T1 for one gauge location.
3.3. Remaining life evaluation and road map From experimental results, the FEM is updated with operating loads and current status characteristics, see Fig.7. From on-line measurements, actual loads are applied on the FE model. The FE model is tuned to correlate simulated stress and accelerations to the measurements. Using the final reliable FEM, the future life of the structure is simulated.
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Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Anne Coulon/ Structural Integrity Procedia 00 (2019) 000–000
Fig. 7. Operating measurement and FE model reliability.
The remaining life evaluation includes different assumptions: Distribution on the network: Only on one line or equitable repartition on all lines, Loads, example: 1/3 full load and 2/3 empty, Service frequency. Finally, the results can be represented on a graph, see Fig. 8. On this example, with current operating loads, the lifetime of the rolling stock is over 40 years. Increasing the frequency to 2 minutes at peak hours will leads to risk of failure after 35 years. According to these results, modifications and reinforcements can be evaluated in the sensitive areas with the FE model.
Fig. 8. Remaining life evaluation results.
If the desired lifetime is not reached, a specific maintenance plan can be defined to control sensitive areas and afterwards structural reinforcements can be integrated.
Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Coulon / Structural Integrity Procedia 00 (2019) 000–000
673 9
4. Conclusion This approach has been applied by VibraTec on different railway structures like bogies, car bodies, infrastructure components, etc. Railway maintenance, renovation and/or replacement costs are major issues for owners. Indeed, remaining life studies are essential to make the right decisions in terms of sustainable development and long-term investments. Operation and maintenance road maps defined from this analysis serve as guides to reach service life objectives. Structural modifications can also be evaluated to optimize life duration. This analysis provides support for investment teams, helping them optimize their asset management strategy. The method presented in this paper is very efficient but needs to be applied with special care and high mechanical expertise. References EN 12 663, Norme Européenne, Applications ferroviaires - Prescriptions de dimensionnement des structures de véhicules ferroviaires, Janvier 2015 Eurocode 3, Norme Européenne, Calcul des structures en acier, NF EN 1993, Juillet 2014 Eurocode 9, Norme Européenne, Calcul des structures en aluminium, NF EN 1999, Janvier 2014 IIW, Recommendations for fatigue design of welded joints and components, A.F. Hobbacher, 2016
Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2019) 000–000
ScienceDirect
www.elsevier.com/locate/procedia
Available online at www.sciencedirect.com Structural Integrity Procedia 00 (2019) 000–000
ScienceDirect
www.elsevier.com/locate/procedia
Procedia Structural Integrity 19 (2019) 665–673
Fatigue Design 2019
Life extension approach focusing on industrial and railway Fatigue Design 2019 applications Life extension approach focusing on industrial and railway Anne Coulona, Julien Fondrata,Nicolas Vincenta, Philippe Négrierb*, Jean-C. Renardb* applications VibraTec, 28 chemin du petit bois, 69131 Ecully, France a Lyon Cedex 03, France b Sytral, 21bda Vivier Merle, CS63815, 69487 a
Anne Coulon , Julien Fondrat ,Nicolas Vincent , Philippe Négrier *, Jean-C. Renardb* a
Abstract
b
a VibraTec, 28 chemin du petit bois, 69131 Ecully, France Sytral, 21bd Vivier Merle, CS63815, 69487 Lyon Cedex 03, France
b
Using its expertise in fatigue analysis, VibraTec has developed an approach to evaluate remaining life aiming to ensure asset durability and optimize operation to extend service life. Remaining life provides visibility of the structure’s future life to anticipate Abstract difficulties and guarantee long-term quality of service. Analysis of this parameter is an important part of asset management for structures designed to for decades, railwayhas transportation. Using its expertise in last fatigue analysis,like VibraTec developed an approach to evaluate remaining life aiming to ensure asset durability and optimize operation to extend service life. Remaining life provides visibility of the structure’s future life to anticipate The approach forlong-term evaluatingquality remaining life is based on aofcoupled digital and experimental fatigue analysis. The difficulties andpresented guarantee of service. Analysis this parameter is an important part of asset management for sensitive areas of thetostructure under study firstlytransportation. determined by Finite Element Analysis according to nominal fatigue loads. structures designed last for decades, like are railway The current status of structural mechanical integrity is studied by concentrating nondestructive examinations on sensitive areas (NDT, magnetoscopy, observation, etc). Then, areand performed to identify theanalysis. real operational The approach presentedvisual for evaluating remaining life operational is based on ameasurements coupled digital experimental fatigue The loads, to evaluate andstructure tune the under Finite study Element Using final reliableAnalysis Finite Element Model, the future life of the sensitive areas of the areModel firstly (FEM). determined by the Finite Element according to nominal fatigue loads. structure is simulated. Different operation road maps can be evaluated to ensure structural durability and extend asset service The current status of structural mechanical integrity is studied by concentrating nondestructive examinations on sensitive areaslife. (NDT, magnetoscopy, visual observation, etc). Then, operational measurements are performed to identify the real operational To conclude the paper, the method is Element then applied to quantitatively thereliable remaining lifeElement car bodies for railway networks. loads, to evaluate and tune the Finite Model (FEM). Usingassess the final Finite Model, the future life of the Operationisand maintenance roadoperation maps serve as maps guidescan to reach service to lifeensure objectives. Structural modification can alsoservice be structure simulated. Different road be evaluated structural durability and extend asset life. evaluated to optimize life duration. This analysis provides support for investment teams, helping them optimize their asset management strategy. To conclude the paper, the method is then applied to quantitatively assess the remaining life car bodies for railway networks. Operation and maintenance road maps serve as guides to reach service life objectives. Structural modification can also be © 2019 The by Elsevier B.V. provides support for investment teams, helping them optimize their asset evaluated to Authors. optimize Published life duration. This analysis Peer-review under responsibility of the Fatigue Design 2019 Organizers. management strategy. © Published by Elsevier B.V. B.V. © 2019 2019The TheAuthors. Authors. Published by Elsevier Peer-review under responsibility of the Fatigue Design 2019 Organizers. Peer-review under responsibility of the Fatigue Design 2019 Organizers.
* Corresponding author. Tel.: +33 472 866 565. E-mail address: [email protected] 2452-3216 © 2019 author. The Authors. Published Elsevier B.V. * Corresponding Tel.: +33 472 866by565. Peer-review under responsibility of the Fatigue Design 2019 Organizers. E-mail address: [email protected] 2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers.
2452-3216 © 2019 The Authors. Published by Elsevier B.V. Peer-review under responsibility of the Fatigue Design 2019 Organizers. 10.1016/j.prostr.2019.12.072
Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Anne Coulon/ Structural Integrity Procedia 00 (2019) 000–000
666 2
Keywords: Remaining life, railway transportation, asset durability, extend service life, digital and experimental operational analysis.
1. Introduction Using its expertise in fatigue analysis, VibraTec has developed an approach to evaluate remaining life aiming to ensure asset durability and optimize operation to extend service life. Remaining life provides visibility of the structure’s future life to anticipate difficulties and guarantee long-term quality of service. Analysis of this parameter is an important part of asset management for structures designed to last for decades, like railway transportation. The approach is then applied to urban car bodies for railway transportation. Rolling stock maintenance, renovation and/or replacement costs are major issues for their owners. Indeed, remaining life studies are essential to make the right decisions in terms of sustainable development and investment for rolling stock owners. Nomenclature
Tnom Nominal life Fnom Nominal load Fact Actual load lim, nom Nominal strength limit lim, act Actual strength limit max, nom Maximal nominal stress Reference acceleration cycle range ref
i
Ni N eq
Test acceleration cycle range
Test number of acceleration cycles Equivalent test number of acceleration cycles
2. Methodology The development process of a new product can be synthetized using a V-Model as presented in Fig. 1. The remaining life methodology developed by VibraTec is based on the same process. Designer requirements Nominal life: Tnom Nominal load:
Acceptance testing Operating loads Actual load: Fact
Fnom
Design and production Design margin: max, nom ≤ lim, nom ? Quality of fabrication:
lim,
act
≤
lim,
nom
?
Fig. 1. Remaining life methodology presented in a product development V-Model
Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Coulon / Structural Integrity Procedia 00 (2019) 000–000
667 3
Determination of load margin coefficient C1: In the requirement analysis phase, the first step in the process, the requirements of the system are collected by analyzing the needs of the user(s). In a remaining life context, the product is operational and actual operational loads Fact are available by measurement in situ. In the V-Model, standard loads Fnom used in the initial development process of the product are updated by the actual loads of the product. The initial design is evaluated regarding the comparison of standard and actual loads. To evaluate the remaining life, the load margin coefficient corresponding to the ratio between nominal and actual loads, for the same number of cycles, is defined:
C1
Fnom Fact
(1)
Determination of design margin coefficient C2: Systems design is the phase where system engineers analyze and understand the business of the proposed system by studying the user requirements document. They figure out possibilities and techniques by which the user requirements can be implemented ensuring the structural mechanical behavior of the product. Many actual products and installations have been designed with old structural analyses, using less efficient FEA tools than current ones. An FE computation with the nominal load is performed. The initial design is criticized comparing the maximal computed stress to the nominal strength limit. The design margin coefficient is then determined thanks to the ratio between the nominal strength limit and the maximal computed stress on the whole structure under the nominal load:
C2
lim,
(2)
nom
max,
nom
Determination of production margin coefficient C3: Then, the structural mechanical integrity of the product is studied by nondestructive examination (NDT, magnetoscopy, visual observation, etc). Strength and quality of material and assembly (welded joints etc) are observed and quantified. The strength limit considered in the initial design is updated and criticized regarding the manufacturing quality. A third correction factor corresponding to the ratio between actual and nominal strength limits is defined to evaluate the remaining life:
C3
lim, lim,
(3)
act
nom
At this step and considering Basquin law, the overall life evaluation can be done using the formula:
Tact Tnom * C1b * C 2b * C3b Then the remaining life is given by:
(4)
Re mainingLif e Tact Age
The last step concerns the validation of the remaining life evaluation according to the potential appearance of cracks or failures on the actual fleet. The maintenance plan and the dated failure inventory must be analyzed since entry into service. This analysis must be completed by the nondestructive examination realized previously. Once the reliability of the remaining life evaluation is validated, operation road maps and maintenance plans for the future life are defined.
Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Anne Coulon/ Structural Integrity Procedia 00 (2019) 000–000
668 4
3. Case study: Car body This approach has been applied by VibraTec on different railway structures like bogies, car bodies, infrastructure components, etc. In this publication, the approach is presented on a concrete car body case. This analysis was done in collaboration with the Lyon transport organization authority Sytral on two rolling stocks: tramway CITADIS and metro MPL75, respectively 15 years old and 40 years old at the study time. Rolling stock maintenance, renovation and/or replacement costs are major issues for their owners. Indeed, remaining life studies are essential to make the right decisions in terms of sustainable development and investment for rolling stocks owners. As described previously, the approach presented for evaluating remaining life is based on a coupled digital and experimental fatigue analysis. First, the current status of car body’s structural mechanical integrity is studied to quantify the relevance of the manufacturing and the initial design. Then, operational measurements are performed to identify the real operational load, to evaluate and tune the FEM. Using the final reliable FEM, the future life of the structure is simulated. Finally, different operation road maps and modifications can be evaluated to ensure the structural durability and extend asset service life. 3.1. Current status The expertise of the car body’s mechanical integrity is based on complementary use of simulation and examination control. A FE model of the car body is built and then standard loads from EN 12 663 (2015) are applied, see §3.1.1. From this FE analysis, sensitive areas are determined and make it possible to focus the examination control on these areas, see §3.1.2. 3.1.1. FE Simulation The FE model is built from paper plans or 3D if available. The modelling approach is based on VibraTec experience. The mechanical structure is modelled, and non-structural elements (covering, equipment, etc) are considered as mass and inertia at center of gravity. The mesh size is defined to be fine enough to compute the stress in sensitive areas like welding areas. All the connections are modelled to represent the mechanical behavior. Mass balance of the model is updated using actual mass of the system. The modelling is done using NX 11 Siemens software and the computation is done with NX Nastran solver. FE models of MPL 75 and CITADIS are presented in Fig. 2. a
b
Fig. 2. (a) MPL75 FE model; (b) Citadis FE model.
Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Coulon / Structural Integrity Procedia 00 (2019) 000–000
669 5
As part of the sensitive area evaluation phase, loads are extracted from EN 12 663 standard. Loads applied to the car body are: o Vertical +/- 0.18g for CITADIS 0.15g for MPL75, o Lateral +/- 0.15g, o Longitudinal +/- 0.2g. To identify the sensitive areas, several computation configurations are studied for each excitation direction considering the most severe connection between bogies and car body. It is noted that EN 12 663 standard specifies a durability of 10 7 cycles for each load direction. Fatigue stress limits of sensitive areas such as weldings are defined according to Eurocode 3 (2014), Eurocode 9 (2014) and IIW (2016). According to the fatigue stress analyses for each load case (Fig. 3), the sensitive areas are determined considering the cumulated damage of each load case. Rivet and screw fatigue behavior are also studied regarding loads transiting in them. All sensitive areas are listed from FE fatigue analysis and then inspected by an expert, see §3.1.2. From these results, the initial design is also criticized comparing the maximal stress computed to the nominal strength limit. This analyze corresponds to the second correction factor of the remaining life evaluation, see §2. Theoretical Fatigue stress limit
Fig. 3. Stress map on CITADIS for vertical load.
3.1.2. Inspection Inspection of sensitive areas is done by an expert from the Institut de Soudure. Visual and nondestructive examinations are done in each sensitive area indicated on 3D, see Fig. 4. Potential cracks are detected (see Fig. 5.) and their criticality is evaluated regarding their propagative status. The strength limits considered in the initial design are updated and criticized regarding the manufacturing quality of welds and their current status in the sensitive areas (C3 coefficient).
Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Anne Coulon/ Structural Integrity Procedia 00 (2019) 000–000
670 6
Fig. 4. Some of sensitive areas to control on MPL75.
Non-compliant Fig. 5. Nondestructive examination.
3.2. Measurements under operating conditions Measurements are done for the different configurations identified during the initial computation (ex: rolling, loading/unloading of passengers, etc) and for situations representative of real service conditions. Sensitive areas defined in §3.1 are instrumented with strain gauges to identify stress cycles. In parallel, several triaxial accelerometers are also positioned on the car body to characterize its dynamic behavior and to register actual operational loads. For rolling measurements, the train speed and localization are also recorded. Comparing nominal loads of EN 12 663 standard and actual loads, the load margin coefficient can be determined. As nominal loads are defined in terms of acceleration cycles, the comparison is done on the effective number of cycles corresponding to the reference acceleration range ref . An equivalent damage analysis is done weighting each acceleration range count by equivalent damage of reference acceleration range using equation (5) from Basquin law:
N eq ref N i i i 0 ref n
The coefficient
b
C1b is then given by: C1b
(5)
10 7 N eq
Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Coulon / Structural Integrity Procedia 00 (2019) 000–000
671 7
Loads on the MPL75 car body are compared in specific operating conditions with empty and full loads to reference in Table 1. Regarding those results, the car body load is an important parameter. Number of cycles count for full load is more than 10 times higher than the empty load in the vertical direction. In full load extreme conditions during the whole car body life, the equivalent number of acceleration cycles is higher than the standard. The same work is done to compare standard to realistic operational loads, corresponding to a specific repartition between empty and full car body loads. These results are not presented here, but enable an evaluation of the initial design. Table 1. Comparison of equivalent and reference number of acceleration cycles on MPL75. Test Direction
Full load
Standard
Empty load
Reference load
Lateral
9.9 104
3.1 105
1 107
Vertical
7.4 10
5.8 10
1 107
7
6
From strain gauge and GPS measurements, stresses are projected on the network, see Fig. 6. This visualization makes it possible to correlate the stress events and the network localization and specificity (rail default, specific curve, etc). Each line is characterized in terms of damage to the car body. The stress events are also compared to the car body dynamic behavior from accelerometers. Finally, measurement analysis makes it possible to correlate the fatigue behavior, the network and the car body dynamic behavior. From this analysis, network operations can be adapted to reduce the car body fatigue damage.
Fig. 6. Stress map on tramway line T1 for one gauge location.
3.3. Remaining life evaluation and road map From experimental results, the FEM is updated with operating loads and current status characteristics, see Fig.7. From on-line measurements, actual loads are applied on the FE model. The FE model is tuned to correlate simulated stress and accelerations to the measurements. Using the final reliable FEM, the future life of the structure is simulated.
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Fig. 7. Operating measurement and FE model reliability.
The remaining life evaluation includes different assumptions: Distribution on the network: Only on one line or equitable repartition on all lines, Loads, example: 1/3 full load and 2/3 empty, Service frequency. Finally, the results can be represented on a graph, see Fig. 8. On this example, with current operating loads, the lifetime of the rolling stock is over 40 years. Increasing the frequency to 2 minutes at peak hours will leads to risk of failure after 35 years. According to these results, modifications and reinforcements can be evaluated in the sensitive areas with the FE model.
Fig. 8. Remaining life evaluation results.
If the desired lifetime is not reached, a specific maintenance plan can be defined to control sensitive areas and afterwards structural reinforcements can be integrated.
Anne Coulon et al. / Procedia Structural Integrity 19 (2019) 665–673 Coulon / Structural Integrity Procedia 00 (2019) 000–000
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4. Conclusion This approach has been applied by VibraTec on different railway structures like bogies, car bodies, infrastructure components, etc. Railway maintenance, renovation and/or replacement costs are major issues for owners. Indeed, remaining life studies are essential to make the right decisions in terms of sustainable development and long-term investments. Operation and maintenance road maps defined from this analysis serve as guides to reach service life objectives. Structural modifications can also be evaluated to optimize life duration. This analysis provides support for investment teams, helping them optimize their asset management strategy. The method presented in this paper is very efficient but needs to be applied with special care and high mechanical expertise. References EN 12 663, Norme Européenne, Applications ferroviaires - Prescriptions de dimensionnement des structures de véhicules ferroviaires, Janvier 2015 Eurocode 3, Norme Européenne, Calcul des structures en acier, NF EN 1993, Juillet 2014 Eurocode 9, Norme Européenne, Calcul des structures en aluminium, NF EN 1999, Janvier 2014 IIW, Recommendations for fatigue design of welded joints and components, A.F. Hobbacher, 2016