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VHS High Strain Rate System

Presentation of the testing Facilities

The test platform is a servo-hydraulic machine with the following nominal features:

  • Capacity of 65kN at high strain rates
  • Maximum jack speed of 25 m/s
  • Temperature chamber between -135°C and +250°C
  • Testing fixtures for traction, 3-point bending (Charpy type), punching
  • Extensometry without contact based on a Doppler-effect laser up to 25 MHz
  • Data retrieval system (load, speed, elongation, accelerometer, etc.) via 8 synchronised 5MHz channels
  • Profiler® System to obtain a virtually constant testing jack speed
  • High speed digital camera (30 000 frames per second)
  • Specific load cells developed at the Centre des Matériaux
Experimentation/numerical Simulation Coupling

Exploitation of such a high speed testing facility to measure the actual high strain rate behaviour of a material is often coupled to numerical simulations in order to dissociate the global response into that due the intrinsic material response and that due to inertial effects. For brittle materials, for example, numerical simulation makes it possible to identify the instant at which the homogeneous deformation of the specimen gauge lengths can be verified.

An inverse approach coupled to optimisation tools developed under the ZéBuLoN finite element code can then provide a robust identification of the material parameters of the proposed material laws.

Expertise

  • Experimental characterisation of material response between strain notes of 0.01 and 300 s-1
  • Development of specific instrumentation for tests at high strain rates
  • Formulation of constitutive material laws appropriate to the phenomena brought into play
  • Determination of the parameters of the constitutive material laws on the basis of an experimental/numerical simulation coupling through a minimisation procedure using an optimisation software
  • Numerical implementation of the constitutive material laws into the ZéBuLoN finite element code
  • Structural calculations at high loading rates

The development of a mechanical test platform at high strain rates at the Centre des Matériaux responds to a growth in the demand for high-speed tests on the part of our industrial partners such as those in the automobile industry and its subcontractors (Renault, PSA, Plastic Omnium, etc.), the aeronautical industry (EADS, Airbus), and the energy and transport sectors (EDF, Europipe, Total, Institut Français du Pétrole, Atofina, Coflexip, etc.). The clear aim is firstly to reduce the time required for the development phase of a new product and secondly, to enable a more accurate prediction of reliability and durability. These objectives are obtained on the basis of the development of predictive simulation tools whereby materials can be chosen for the various components according to applied mechanical loading conditions.

The development of such simulation tools involves an indispensable phase which is the experimental description and modelling of the behaviour of a wide range of materials. Many applications require knowledge of the materials behaviour for a range of strain rates varying from 0.01 to several hundred s-1. An example of this are the conditions prevailing in crash-tests performed by the automobile industry. The non-linearity of the relationship between a material stress-strain response and strain rate (illustrated in the figures herewith) does not permit a sound extrapolation of the quasi-static response of materials and requires experimental determination. It is in response to this strong industrial need that a specific experimental procedure has been developed at the Centre des Matériaux to underpin the development of elastoviscoplastic constitutive laws for structural materials.

Types of materials studied

By virtue of its expertise and the diversity of its research themes, the Centre des Matériaux can boast of substantial experience in the modelling of the behaviour of metallic materials, composites, elastomers, polymers and metallic foams. At present, constitutive modelling of metallic materials and composites at high strain rates accounts for a substantial part of the research work conducted using this equipment.

Contacts

VHS High Strain Rate System - MINES ParisTech
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