More reality in virtual crash tests

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Dynamic tests, assessments and improvements

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Reliable modeling and characterization of joints

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Crash Safety and Damage Mechanics

We develop and implement material and failure models and utilize them in crash and process simulations. We also use special testing techniques (e.g. local strain measurements, torsion and biaxial tensile tests) to characterize materials and test components. By simulating various trials, we determine the model parameters and validate the practicability of new numerical methods. The effects of manufacturing processes on component behavior are paid particular attention.

Modern CAE-assisted developments require characteristic material parameters that correspond to specific load situations in order to produce designs and assess safety. Crash-relevant material values related to the strain rate or load speed are also needed to determine vehicle crash safety or accident-related impact loads on transportation containers: we determine the values for different materials and joins via high-speed tests that involve high-speed video and infrared cameras as well as optical evaluation processes. Our component crash tests are used to validate numerical simulations and provide conclusive assessments.

We characterize the mechanical properties of joints and assess them in terms of their deformation and failure behavior. A particular focus of our work is joint modeling for crash simulations, as this is the only way to analyze such a large number of different joints in the whole vehicle structure, thousands of them, and predict their capacity. By simulating joining processes such as punch riveting we are able to determine the aspects of the process that influence the joint properties.

What we offer 

 

  • Characterization of deformation and failure behavior under different types of load
  • Component trials under realistic loads
  • Development and verification of material models and numerical methods for crash and process simulations
  • Failure modeling that is consistent in both crash simulations and forming/casting simulations
  • Simulation of aluminum profile extrusion with microstructural calculations
  • LFT crash simulations linked to form filling simulations
  • Assessment of the crash safety of battery housings
  • Vehicle safety and misused/crashed lightweight designs: crash-like material characterization and identification of crash parameters as the basis for crash simulation material cards as well as component crash tests for verification and assessment purposes
  • Container safety on impact: impact load tests on samples similar to the component or the components themselves including analysis and assessment
  • Plant safety in the event of an accident/breakdown (fracture dynamics): fracture dynamic material characterization at high crack stress rates for the analysis of thick-walled, cracked structures
  • Optimizing high-speed forming processes: dynamic Nakajima deep drawing tests with detailed optical 3D deformation analyses using high-speed video cameras and ARAMIS in order to determine forming limit diagrams
  • Development of testing methods with which to characterize materials and joins under complex single and multi-axial loads
  • The use of modern high-speed metrology such as high-speed infrared measurements and 3D high-speed video analysis of rapidly changing strain fields
  • Characterization and assessment of lightweight constructions, joins and innovative materials on impact and in crash situations
  • Characterization of the mechanical properties of joints and joined components
  • Deformation and failure modeling for joints
  • Investigations into damage and fracture mechanisms
  • Development of substitute modeling methods for joints in crash simulations
  • Characterization and modeling of joint failure (spot welds, laser welds, punch rivets and adhesive bonds) under crash conditions
  • Assessment and optimization of factors influencing a process with joint process simulations for punch riveting, welding etc.

Material deformation, damage and crack formation

Global and local material behavior of fiber reinforced plastics

Topics

 

Material and component deformation and failure behavior

 

The characterization of a material’s deformation and failure behavior sets the foundation for reliable design and numerical simulations. At the IWM, we perform specialized tests that subject the sample to tensile, compressive and shear stresses in order to determine the effects of multi-axiality and load type on failure behavior. Component tests at up to 8 MN can be carried out to validate simulations... 

 

Failure models for crash simulations

 

The Fraunhofer IWM has developed material models that accurately describe the deformation and failure behavior of new materials and are integrated into commercial crash codes as user material routines. For example, our damage models and phenomenological models, which account for “honeycomb” and shear fracture, can be used to model micromechanical failure. We have also developed and implemented pressure-related material models that ...

 

 

 

Modeling the failure behavior of long fiber thermoplastics (LFT)

 

The behavior of LFT components can be easily predicted thanks to the combination of mold filling and crash simulations. The simulation accounts for the distribution of fiber orientation and fiber thickness. The material model is based on homogenization methods. The first step is to approximate the unidirectional properties of the composite with a transversally isotropic rigidity matrix. Empirical methods are used to implement damage development. The second step ...

 

 

 

Crash simulations 

 

Crash simulations are performed in order to assess the crash safety of various components and validate the applied material models; the results are compared to those of component trials. The commercial PAM-CRASH, LS-DYNA and ABAQUS crash codes are often combined with user material models. In order to account for the effects of manufacturing processes on crash behavior, one can, for example, transfer pre-stretching and previous damage from deep drawing simulations or porosity from ...

 

 

 

Deformation and failure of lightweight materials under crash conditions

 

The focus here is on the characterization of different lightweight materials such as high-strength steels, light metals, foams, FRPs and joints in relation to expansion rate under multi-axial loads from quasi-static to crash-relevant load speed. The investigations are carried out using modern, high-speed testing equipment and high-resolution measuring techniques, and non-contact ...

 

Dynamic component behavior

 

Components can be subject to dynamic loading in the form of a momentary impact either during operation or in the event of an accident. Engineering or power plant components that experience this particular type of abrupt loading include shafts or turbine blades. Crash-like loads are also one of the most important factors in vehicle design. The loading rate that can be realized with existing testing equipment is approx. 100 m/s, the time-to-failure lies in the millisecond to microsecond range...

 

 

 

Fracture dynamics

 

A special form of momentary impact can occur when operating technical equipment. So far, safety has been assessed in the same way as static loads, with additional safety factors that account for the dynamic effects. High-speed testing techniques for these particular load situations have been developed while probabilistic, fracture mechanical assessment methods based on the master curve concept have been tested in component trials in order to improve the safety assessment. The results show that ...

 

 

 

Substitute modeling for crash simulations

 

A reliable and practical description of joint failure in crash simulations depends on special elements, so-called substitute models and their input data. The Fraunhofer IWM has developed a simple, efficient substitute model and a technique for determining the failure parameters for spot welds. A material model has also been implemented for modeling the failure of adhesive bonds with parameters that have been determined from substance and joint samples and ...

 

 

 

Modeling the deformation and failure of spot welds in hot-formed high carbon steels

 

The development of new high strength steels for use by the automotive industry has created the potential for lightweight designs that combine thin walls and low weight with high strength, rigidity and passive safety. So-called softening zones form when welding hot-formed, 22MnB5 boron alloy steels; these zones are much weaker than the surrounding material. The effect of ...

 

 

 

Advanced substitute model for punch rivets joints

 

Mechanical joining techniques have the advantage that they can be used to join different types of materials in a safe process, without the negative effects of heat on the material properties. A number of mechanical joining techniques, such as semi-tubular punch rivets and direct screw joints are therefore used on multi-material mixes in automobile manufacturing. Until now, there has been a lack of simulation models and characteristic joint data that would ...

 

 

 

Modeling of adhesive joints


By avoiding local stress concentrations, adhesive joining can offer advantages in light-weight structures compared to mechanical fasteners. For a reliable component design the load carrying capacity and failure behavior of the adhesive joint has to be understood and simulation methods are required to be as accurate and as efficient as possible. Cohesive zone models are often used to meet both requirements. In order to provide the necessary material behavior data, scientists at the Fraunhofer IWM experimentally characterize adhesive joints, which can account for additional effects such as loading rate, temperature and humidity. Local details may furthermore be studied by high-discretization continuum mechanics modelling of the deformation and damage behavior, which can be included into the component modelling.

 

Calculation of residual stress and warping during welding

 

The heterogeneous nature of welding in which the material is heated up locally and cools down induces internal stresses and leads to component distortion. This has a negative effect on component quality and functionality and can also cause damage, e.g cracks, and/or reduce the service life. Internal stress and distortion are closely related, and many factors lead to their generation. The material properties, clamping conditions as well as ...

 

 

Assessment of the load-carrying capacity of a spotwelded metal sheet with a softened heat affected zone

 

The spotwelding process is still the most commonly used joining process for body-in-white manufacturing. More and more, high-strength steels are being utilized and welded. However, high-strength steels such as 22MnB5 and HCT980C will form a softened heat affected zone around the spotweld due to the heat treatment during the welding process...

Crash Safety and Damage Mechanics publications

 

Contributions to newspapers, books and conferences as well as dissertations and project reports...