PSA Peugeot Citroën leverages nCode DesignLife to investigate and predict fatigue life of automotive components and subsystems

Passenger cars are subject to vast loads and rough operating conditions in their day-to-day use. Even when enduring the worst roads or driving conditions, all vehicle components and subsystems have to operate properly and reliably. The challenge car makers face every day is designing cars to withstand all possible use cases during their entire product lifecycle. Therefore, significant effort is required to predict and test the fatigue life of vehicle systems and components in order to improve quality, prevent failures, and lower warranty costs. To support these investigations, PSA Peugeot Citroën uses nCode DesignLife software within their development processes for fatigue analysis.
Fig. 1: Typical workflow of a fatigue investigation
PSA Peugeot Citroën is a world-class automobile manufacturer, offering two well known brands, Peugeot and Citroën. With operations in 150 countries, the company is actively expanding its sales in new, fast-growing markets. PSA Peugeot Citroën demonstrates a commitment to innovation in the areas of safety and environmental protection in order to develop and build cars that meet the high expectations of Peugeot and Citroën customers around the world. In the Numerical Engineering department of PSA, called “Calcul et Ingenierie Numérique” (CINM), several teams are dedicated to developing methodologies, executing calculations and validating results for the powertrain and suspension areas. In this context, PSA engineers also handle fatigue life investigations conducted using nCode DesignLife. These simulations enable the teams to make fatigue life predictions based on results from finite element analysis, helping them answer questions such as “how long will it last?” or “will it pass the test?” even before a physical prototype is built.

Fatigue evaluations at PSA Peugeot Citroën

In the past, PSA powertrain and suspension used its in-house fatigue code, PSA-Fatig, which is based on the Dang Van criterion, a method to predict endurance limits under complex loading situations. The Dang Van criterion is classified as a ‘micro-structural’ method because it considers stresses and crack initiation at the local level. Unlike other methods, output from the analysis is always expressed as a safety factor as opposed to fatigue life.
To further streamline its development process, PSA looked for fatigue software packages that included their historical Dang Van criterion approach for validating fatigue resistance and other beneficial features such as proven fatigue approaches, an advanced user interface, and the ability to prototype new methods via scripting. Since all of PSA’s validations for fatigue resistance are based on the Dang Van criterion, it was essential that any alternative software tool covered this approach in order to achieve time and cost savings in the development process.
After an extensive evaluation of nCode DesignLife, in which the software was compared to PSA-Fatig, PSA selected nCode to handle fatigue analysis in its powertrain and suspension development areas. Along with scripting and interface features available in nCode, PSA engineers appreciated its ability to import finite element results from Abaqus (Dassault Systèmes) and MSC Nastran (MSC.Software). nCode DesignLife is applied on volume parts for powertrain development and on sheet metal parts within the suspension, including investigations on seam welds as well as spot welds. HBM Prenscia, developer of nCode DesignLife, provided PSA engineers with training and support throughout the deployment phase and worked with PSA to configure software to their specified needs.
Fig. 2 : Mesh and loads applied to the engine cradle

nCode DesignLife in the development process

The objective of a fatigue life investigation is to evaluate the fatigue strength of parts or components. If a calculation shows that the fatigue strength cannot be ensured, the geometry of the part has to be modified until it meets the criteria. A typical investigation consists of loading results (stresses) from a finite element analysis (i.e. from Abaqus or Nastran), applying certain load conditions, and performing the fatigue analysis itself (with Dang Van criterion or other). The results, such as contour plots of danger factors, are then displayed. The results of the fatigue analysis are written into a file that can be reloaded into PSA’s standard post-processing software, HyperView from Altair Engineering.
The following example showcases a fatigue evaluation of an engine cradle. A finite element analysis has been performed with Abaqus. Several loads case describing a loading cycle on the cradle have been applied. In the next step, the finite element results are loaded into nCode DesignLife (via the FE Input Glyph) and have been sent to the fatigue analysis Glyph (Dang Van). The user then defines the material parameters according to the Dang Van criterion (parameters HSS and TAFE) and the results are displayed on a FE Display Glyph and written to a file. This analysis can be performed on both the metal sheets (Fig. 3) and the spot welds (Fig. 4).
To handle spot welds (ESW), HBM Prenscia implemented a specific treatment in the Dang Van Glyph as requested by PSA. This customized development step enables PSA to perform the same type of calculation as with PSA-Fatig. The FE model of the ESWs uses beams, and in this case, the input data to nCode DesignLife (FE input Glyph) are the forces expressed on the nodes of the beams. The specific treatment implemented in nCode DesignLife allows these forces to be converted into stresses around the ESW, and then the Dang Van criterion can be calculated.
Fig. 3 : Fatigue analysis of an engine cradle with nCode DesignLife and the Dang Van criterion, results on plain metal sheet
Fig. 4 : Fatigue analysis of an engine cradle with nCode DesignLife and the Dang Van criterion, results on electric spot welds (ESW)

Benefits, conclusions, and outlook

PSA Peugeot Citroën has reached a milestone in their development process by using nCode DesignLife for fatigue evaluations. By implementing new criteria for fatigue analysis, PSA is now able to develop new methodologies, decrease physical tests, and achieve more accurate results. This will lead to more cost-efficient and less time-consuming development processes.
Additionally, PSA engineers are able to perform more numerical investigations to better determine any design changes needed to meet targeted component performance. They are also able to handle evaluations of varying size and scope, resulting in analyses that are more robust, predictive, and adaptable to specifications required for different applications (vibration fatigue, composite materials…). PSA plans to replace PSA-Fatig with nCode DesignLife in all divisions performing fatigue evaluations for applications ranging from powertrain to the entire body of the vehicle.

“In addition to using the Dang Van criterion and the other fatigue analysis capabilities nCode DesignLife offers we especially enjoy the user interface of the software and its operations based on pre-defined processes called Glyphs. We also appreciate the scripting capability that enables us to create more customizable analyses.”

Philippe Bristiel, Ph.D. in mechanical engineering, in charge of the support and the development of methodologies for fatigue analysis and structural optimization at PSA Peugeot Citroën.