Final Report Summary - REFRESCO (Towards a REgulatory FRamework for the usE of Structural new materials in railway passenger and freight CarbOdyshells.)
The transportation industry has for a long time been engaged in the application of new lightweight materials for primary structural design. The use of such materials is vital to achieving reductions in energy consumption and consequently to achieving reductions in greenhouse gas emissions. For instance, in aeronautics, where the weight of an aircraft is a critical factor for fuel consumption, composite materials are replacing metallic materials in both structural and non-structural parts.
The railway industry could also benefit from the use of structural new materials. The weight savings associated with the use of these new materials would result in reduced power consumption, lower inertia, less track wear and the ability to carry greater pay-loads.
However, the implementation of such materials in the rail industry has been slow, mainly due to the lack of suitable certification procedures addressing the specific operational requirements of a railway vehicle. Therefore, the overall objective of REFRESCO was to set the regulatory framework for the rapid, efficient and safe implementation of new lightweight materials in the railway sector through the evolution of certification processes for railway rolling stock.
REFRESCO addressed this difficulty by looking at standards and processes that needed to be updated or changed to allow the introduction of lightweight materials. REFRESCO paved the way for the certification of new materials, taking into account the certification routes adopted by other transportation sectors and at the same time addressing the challenges that are unique to rail carbody construction without compromising safety. The research covered topics such as strength, crashworthiness, fire resistance, noise and vibration performance, electromagnetic compatibility (EMC) and maintainability of the composite materials.
The main conclusions of the project were:
• WP2: A set of materials and standards need to be reviewed or created.
• WP3: Different physical and electrical characteristics of the composites affect functionality of some areas into the vehicle system.
• WP4: Actual knowledge in composites allows their use for structural purpose with some limitations.
• WP5: Slight adjustments on design and validation processes are needed.
• WP6: Acceptance criteria are needed for railway sector for both manufacturing processes and joining methods.
• WP7: Non-destructive technology and maintenance philosophy are available for composite material thanks to aeronautic experience.
• WP8: Experience from aeronautic sector in NDT is valid for railway purposes.
Moreover, in order to ensure the uptake of the results, the project developed a summary document that presents recommendations for the modification of current railway standards to allow the safe introduction of new materials in train carbodies. The document incudes the findings from the research conducted in each work package and how this affects current standards. The REFRESCO recommendation for standardisation will help developing a technical specification in the field of railway lightweight materials. The project’s recommendation for standardisation has been distributed among the SC2 of the CEN/TC256.
All the public deliverables can be found at http://www.refresco-project.eu
Project Context and Objectives:
The overall objective of REFRESCO was to set the regulatory framework for the rapid, efficient and safe implementation of new materials in the railway sector through the evolution of certification processes for railway rolling stock. The specific objectives for each WP were to:
WP2: Benchmark material solutions available to railway and other sectors and investigate any gaps in current standards or certification process that could affect the introduction of lightweight materials in the railway sector.
WP3: Investigate the impact of Fire, Smoke and Toxicity, Noise, Vibration and Harshness and Electro Magnetic Compatibility properties of lightweight materials when used in a train carbodyshell.
WP4: Understand the structural requirements concerning fatigue arising from the replacement of metal with high performance composite materials in rail carbodyshells.
WP5: Provide recommendations on the design and validation process for body structures partly or wholly made of composite materials.
WP6: Develop quality criteria and validation methods for the manufacture and joining of structural elements made of composite and sandwich materials or hybrid structures.
WP7: Analyse damage scenarios, implement a defects catalogue and a methodological guide on health monitoring taking into consideration the experiences from the aeronautic sector.
WP8: Evaluate the repair technologies for new lightweight materials as well as propose a repair criteria and a maintenance strategy suitable for the safe operation of the composite/hybrid structure of the train carbody.
WP9: To develop a proposal for standardisation report based on the results of the project.
The most important results of the project are described below:
WP2: A comprehensive list of materials used in the rail sector and other sectors have been compiled and inserted in a matrix with all the material properties available. Unfortunately, not all the required material properties were available. This was principally due to issues surrounding confidentiality. It was extremely difficult to obtain information from organisations since the nature of composite materials, in particular their modes of failure depend very much on the specific application and components of the composite.
A requirement matrix was produced, which is divided in a matrix for safety requirement and a matrix for functional requirements. In those matrices, all relevant requirements are determined, which are necessary to manage the impact when composite materials for rolling stock carbodies are introduced.
Best practices from other industries have been identified showing how compliance can be proven. Most of the information is taken from aeronautics and marine industry. Reference is made to the relevant sections of the standards. For strength and crashworthiness, the railway standards need to be adapted. Reference is made to standards and best practices from other industries.
Raw material properties could be found to estimate the properties of the alternative material to be used during the research. A final recommendation on the rough/composite materials to investigate for the other WPs was finally issued indicating different raw materials and material structures.
WP3: Some materials compliant with EN45545 have been found but as the standard is relatively recent not many materials have been certified against it. It is likely that in the future more materials will be certified against EN45545 and new opportunities will arise to design lighter rail vehicles using composites. In addition, FST design guidelines have been proposed regarding on families of materials, material architecture and possible future material developments.
From the literature review, it was seen that the lightweight combined with a high stiffness leads to the main drawback of composite materials: an efficient acoustic radiation. However, damping of composite material, adapted geometry and ability to fulfil several functions give opportunities to face this drawback. Some attempts to optimize the vibroacoustic behaviour together with other criteria, such as thermal insulation, strength, and others have been described in the literature. They are limited to computation of partial criteria, such as transmission loss, taking into account only the acoustic part of the excitations.
To improve the optimisation process with an acoustic constraint, two ways have been proposed. The first is to consider all the sources like the structure borne part of the interior noise. The second way is to evaluate the harshness with psycho acoustic criteria. This process of multi objective optimisation has already been done for the composite structure of aircraft, and in the railway industry on high speed train.
The use of composite materials has both positive and negative impacts. Positive impacts are for instance found on the electric field inside the carbody. The electric field inside the carbody due to emitters inside or due to electromagnetic wave coming from outside since resonance phenomenon gets reduced by composite materials. It shows that shielding effectiveness has not a significant influence since the preponderant phenomenon are reflections and resonances especially windows resonances. It has negative impacts on the return currents between 50 Hz and 150 kHz. Introducing composite materials leads to voltage drops on equipment which is four times higher for CFRP vs aluminium. Those return currents can be expected currents between two pieces of equipment or parasitic currents due to, for example, lightning strokes on the catenary. This impact needs to be considered for the case of catenary falls: the short-circuit current flowing into the rails and resulting from a catenary fall will be very low in the case of a structure made of insulating composite like GFRP and it could be very difficult for the circuit breaker to detect.
WP4: A characterisation of composite materials in railways for structural calculations was made and the findings have been included in this deliverable. It also proposes a guideline for determining the properties of a polymer matrix composites system for a structural application, in order to be able to perform analysis with finite element modelling, as well as several test matrices are proposed, based on the state of the art in aerospace.
According to the analysis, the Hashin's Failure criterion seems to be the most suitable for fatigue calculation, based on aerospace experience.
WP5: From the analysis of collision scenarios on the carbody models, it is found that the main current section of the carbodyshell structure should be designed to resist the collision loads without exceeding the elastic limit of the composite materials used. Also, design requirements for front cab structure were given, detailing the behaviour of side poles. Remark has been made that validation test methods should be developed to ensure the repeatability and the robustness of energy absorbing device and obstacle deflector designs. Benchmarking of relevant software (Ls-Dyna and Radioss) revealed that both have the capability to model composite materials.
It is described the different methods of modelling composite materials families listed in work package 2, with finite element software commonly used for crash applications in railway (in the frame work of Refresco project, Radioss and LSDyna are investigated). For each method, it recommends the most relevant properties and material laws for the simulation software to best represent and predict composite behaviour during crash simulations at train level required by EN15227.
Recommended property and material laws are detailed to highlight physical parameters that have to be characterised and measured from sample tests. Then a list of typical tests is provided to cover monolithic and sandwich characterisation.
Reference simulations on metallic structures respectively on a passenger and a freight vehicle are performed to get the crash responses on two types of rolling stock complying with EN15227. Composite materials are then introduced in the cabin structures, using the material characterized from the sample tests. In these conditions, the crash simulations of the two types of rolling stock show the failure of the composite beams, whereas the original structures were deforming, due to the ductility of metal. The inherent lack of ductility of composite materials is here confirmed on complete structures. The composite cabin structure is then reinforced and passed the crash requirements. It is also demonstrated that the crash response depends on the modelling details like the mesh size and the elements formulation applied to the composite components. Therefore, composite materials could be used for crash applications, if appropriate characterisations of the materials and the components are used.
WP6: Different manufacturing processes were screened and clustered into process groups. For each of these process groups, some relevant sub-processes and their related attributes and process parameters were identified. It was obvious that the different processes and process parameters could directly influence the final quality, performance and cost of the structural composite parts. In order to get an understanding of the variety and structure of the influencing parameters, the usage of a parameter tree was proposed. A shortlist with parameters for all processes was created in order to underline the importance of process control.
Standards and approaches used within the composite industry for incoming goods control in -process control and first article inspection have been highlighted. For a cost effective assessment of companies and manufacturing sites a distinction into three different part classes have been proposed. Gaps in the regulatory framework have been highlighted, a recommendation for the use as a base of different norms in relation to the part classes has been given and a recommendation for the structure of a future framework for manufacturing acceptance has also been made.
Meaningful combinations of joint and material have been shortlisted, existing potential processes have been analysed and described and examples from different industries are given. For bonding, welding and mechanical fastening exemplary parameter trees have been created. The status of standardization for joints in the Rail industry is shown including some proposals for further improvements.
Destructive and non-destructive test measures have been investigated to become able to have acceptance criteria in manufacturing. These measures have been clustered to the three most relevant joining principles. Gaps in the Regulatory framework have been highlighted. A recommendation for the use of the different norms in relation to the material has been given. A recommendation for the structure of a future framework for joining principles has been made.
WP7: A description of the general inspection practices used in the railway sector has been done, together with a benchmark of Damage Tolerance (DT) strategy. It is also described the state-of-the-art (SOTA) of Non-Destructive Testing (NDT) and Prognostic and Health Monitoring (PHM). All these topics are participating to consolidate an optimized “Life Cycle Cost” for multi materials carbodyshells integrating the appropriate material at relevant areas with the appropriate preventive maintenance plan. For NDT, the relevant method has to be selected among all the existing ones depending of the kind defect and their position. For PHM, due to cost of sensors, as for aeronautic sector, it is recommended to favour their use for commissioning and qualification stages.
A classification of damages on carbodyshells was made and every damage scenario has been identified with a code for future references. For each mentioned scenario, this task has identified the potential damage area and an order of magnitude of the damage. A first conclusion can be that the new design must use the mandatory standards and must remain specific to railway rolling stock. A part of this regulation should be modified and adapted to new materials (seen in WP2 and the relevant technical ones). There exist various national standards which regulate different aspects of scenario of damages; it is recommend to harmonise these. The damages that occur are very different, a classification considering causes, severity, and frequency is very difficult. A database of damages with the capability to evaluate damages by means of statistical analyses. For the future it is recommended to develop such a database.
It is recommended the “Large visual inspection” concept for damage detection instead of “Barely Visible Impact Detectable” used in the aeronautic sector.
For Non Destructive Tests: Relevant tools and known methods are perfectly usable and useful. For Structure Health Management: As this technology is not very mature yet, it should be limited to sensitive areas & Qualification and testing stage. At short term it is recommendable a robust sizing process & relevant tolerance damage strategy. However, the Structure Health Management technology will contribute to reinforce at mid-term LCC performance for operators.
WP8: The methods used to repair multi-material carbodyshells are quite different to the metallic repair in railways sector. These repair techniques are likely to be as the ones applied in the aeronautic sector, as structural performance of the vehicle carbodies is also similar. Also Non Destructive Tests appear to be the preferred method for analysis of the defective areas.
The repair efficiency seems low. The average efficiency reached with liquid infusion methods to repair composites achieves around 90%. Basically the issue behind this phenomenon is that there is not continuity between the fabrics on the specimen and the patch used to repair. The geometry of repaired area seems also to be direct cause of the difference in efficiency. Another way to possibly increase performance of the repair might be the use of one or some extra layers.
Sensors on structural parts are necessary to achieve the maximum experience of the material behaviour as soon as possible, and the predictive maintenance is identified as key factor. The determination of the real in-service condition for the composite is one of the main objectives for the fatigue assessment. For this reason, it is necessary to place sensor in the most stressed part of the carbody. In order to obtain load spectra a cycle counting method should be done with all the measurements. With this information is possible to assess and correlated numerical simulation/hypothesis with real measure. In joints connecting the different elements of the structures sensors are also needed in order to assess the design criteria, therefore forces and stresses near the joint section should be measured. Once again, a certification process is necessary for repairing and maintaining these structures. EN 15085 and the ones in the aeronautic sector may be taken as reference. Despite all these control measures used basically in the test and phases, the use of composite materials, could reduce around 25% in maintenance costs according the aeronautic practice.
WP9: A document which includes the recommendations for standardisation extracted from the research conducted in each WP was written.
REFRESCO carried out research towards adapting the current regulatory framework enabling the use of new structural materials in rail carbodyshells. The project produced the following outcome:
• Contribution to European standardisation with a Technical Recommendation document which includes the recommendations for standardisation extracted from the research conducted in each WP. The document gives details about current standards that should need to be modified, the safety parameters to be modified as well as the characteristics on new materials to be defined in the standards. This document will be used by CEN/ TC256 to open a work item on railway composite materials.
It is expected that the results of this project will:
• Help the development/amendment of railway standards. In particular, this work provides input for most of the parameters that need to be addressed if new lightweight materials are to be introduced in railway carbodies.
• Contribute to the reduction of energy consumption of the railway. Trains made of lightweight materials can reduce the energy consumption of a railway vehicle.
• Improve the competitiveness of the railway industry. Trains made of lightweight materials can be more competitive as they consume less energy, produce less track wear or can carry greater pay-loads.
• Contribute to create new skilled job opportunities in the railway sector. If new materials are to be developed for rail carbodyshells, workforce specialised in these materials for the use in railways will be needed.
• Produce innovative and improved products. The use of new materials in railway would improve the final product.
List of Websites:
Web site: http://www.refresco-project.eu
Avenue Louise 221, 1050 Brussels (Belgium)