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Material behavior at high deformation rate
When subjected to high deformation rates, material response may show substantial differences. In metals and alloys, increasing the strain rates causes an increase of the yield stress, of the work hardening slope and changes the failure strain. The knowledge of the effective response during dynamic transient is critical for an effective and accurate design. At TECHDYN we have more than 25 years of experience in modelling, simulating and testing materials at high strain rates.
A complete set of capabilities
During the years, we have developed competences and unique capabilities for comprehensive investigation of material behavior over wide strain rate range. Our capabilities include:
- Material modelling. Development of material models using empirical, semi-empirical and physically-based formulations to account for strain rate, temperature and microstructure evolution.
- Numerical simulation. Simulation of high strain rate deformation processes (impact, stress wave propagation, shock compression, etc..) by means of explicit finite element codes and hydrocodes.
- Experimental testing. State-of-the-art testing equipment for material characterization and model validation over a wide range of strain rates which includes:
Direct tension Hopkinson pressure bar. This bar configuration allows to perform both tension and compression tests generating the required stress pulse. The stress pulse is generated pretensioning (or precompressing) a portion of the input bar. Accurate test repeatability is ensured by means of strain gauge measure based control. The release is obtained by breaking a brittle joint which ensure full control of stress pulse rise time. The bar set-up has visual access to the sample that can used for in situ and real time measurement using DIC. Tests can be performed from 500/s up to 10.000/s depending on the candidate material and sample geometry. Tests can be performed over a temperature rangng from -196°C up to 1300°C.
Gas gun. TECHDYN has design a single stage light gas-gun for ballistic impact tests. The gun is designed to perform tests with different gun calibers, ranging from 40 mm down to 6 mm. The gun uses helium as propeller gas with a maximum reservoir pressure of 200 bar. Tests are performed in vacuum and samples can be soft-recoverd in ballistic gel. The vacuum chamber allows direct visual access to the target section for high speed recording. The gun capacity is 1000 m/s with 15g projectile mass. This allows the system to perform ballistic impact tests in accordance with NATO STANAG 2920 and STANAG 4569. The gun is routinely used to to carry on Taylor cylinder impact tests, Symmetric Taylor impact ("Rod-on-rod"), Dynamic Tensile Extrusion (DTE) test and ballistic impact tests.
This quality of work would not be possible without state-of-the-art equipment, and TECHDYN has invested heavily to ensure our experts have access to every tool they need to satisfy our customers’ requirements. Recent acquisitions include the following:
- Direct tension Hopkinson pressure bar for testing (tensile or compression) up to 104/s from -190°C up to 1300°C
- Torsion Hopkinson pressure bar
- Single stage, light gas-gun with different calibers (40mm - 6mm) for:
- impact tests up to 1000 m/s with 15 g projectile
- Taylor cylinder impact test
- Symmetric Taylor cylinder impact tests ("rod-on-rod")
- Dynamic Tensile Extrusion test (DTE)
- High precision torsiometer
- High speed camera (1M fps)
- 3D Digital Image Correlation (DIC)
Examples of our recent material characterization:
- Mechanical behavior of 3D printed Ti-6Al-4V at high strain rates
- Fracture locus determination of austempered ductile cast irons
- Fracture assessment of a gas pipe accident
- Mechanical characterization of Tungsten (W) alloy under high velocity impact
For more information, please contact us.