Richter M, Oberhofer G, Dell H, Gese H, Duddeck F:
A phenomenological material model for thermoplastic textile composites for crashworthiness simulation combining a stress- and strain-based failure criterion
Textile-reinforced thermoplastics are a useful material in
light-weight designs, but it is difficult to predict their complex
plastic behaviour and their failure in crash simulations. This paper
proposes a new macro-scale model based on different mechanical
phenomena on micro-scale. An exemplary experimental characterization
of an organic sheet is presented followed by a novel material
characterization for the modular material model MF GenYld + CrachFEM.
Thin-Walled Structures, Volume 184, March 2023, 110490
Holfelder P, Brenner F, Rund M, Witte A, Junghans S, Seyfert C, Richter M, Dell H, Koukolikova M, Gese H, Dzugan J:
Finite-Element simulation of plasticity and fracture of Inconel 718 deposited by LPBF – chance, uses and challenges
Laser Powder Bed Fusion (LPBF) can create parts that have properties that
cannot be achieved with classical materials and whose behaviour can be
tailored by adjusting the process parameters. Numerical models can help
to exploit the full potential of additively manufactured materials. COMTES
FHT carried out comprehensive experiments that revealed a significant
orthotropy of plasticity and fracture. This orthotropy can be modelled with
the material model MF GenYld + CrachFEM. Suitable characterizations for
various parameters showed good agreement between physical tests and
finite-element simulations for Inconel 718.
Additive Manufacturing Tage, Web Conference, 22–23 Feb 2022
Koralla S, Tiwari S, Kahre P, Daphal P, Gese H:
Engineering challenges in alloy wheel rim for safety simulations
The rim of aluminium alloy wheels is one of the critical components in
frontal crash tests. Determining failure characteristics of an alloy wheel
poses many difficulties considering its brittle nature, porosity and
inhomogeneity in material properties across different regions of wheel rim
due to mold design, cooling rate and other process parameters of the
low-pressure die casting process. This paper describes the modelling and
simulation method developed to predict failure of the wheel
rim and the associated tire blowout.
SIAT International Conference 2021
Richter M, Dell H, Oberhofer G, Gese H, Duddeck F:
Material modeling of textile reinforced composites with respect to fracture initiation and strain rate sensitivity
Semi-finished
products with woven textile structures show a promising potential for the
substitution of Al or Mg in structural parts conventionally manufactured
with ductile steel sheets. Endless glass-fibers are woven into plain,
twill or satin weaves and embedded into a ductile thermoplastic matrix.
This study outlines how the modular material model MF GenYld + CrachFEM
can describe the combination of brittle high-strength fibres and
a ductile matrix.
8th ECCOMAS Thematic Conference: Composites, 24 Sept 2021, Göteborg
Richter M, Dell H, Oberhofer G, Gese H:
A phenomenological material model for simulating additively manufactured materials with orthotropic properties
The additive manufacturing process of metallic or polymeric components
yields a highly anisotropic layered structure. An experimental programme
investigates that anisotropic deformation and failure behaviour and the
material model MF GenYld + CrachFEM is used to assess the behaviour
of such structures under misuse loads in FE simulations.
DVM-Conference 2019
Richter M, Gese H, Dell H, Oberhofer G, Duddeck F:
Surrogate modeling of hybrid material pairings including organic sheets
Laser-welded sheets of different organic sheets are tested. The results of
these experiments are used to develop surrogate models to represent the
deformation and failure behaviour of the joints in a simulation complying
with industrial discretization. The finite-element model employs a
phenomenological material model to coverthe full range of the organic
sheet’s fracture initiation from a brittle mode in fiber direction
to a ductile mode in off-axis orientations.
4th International Conference Hybrid 2020 – Materials and Structures,
28–29 April 2020, Web-Conference, Germany
Groß M, Oehm M, Richter M, Oberhofer G:
Integrative Crash Simulation of Short Fiber Reinforced Thermoplastics (SFRT)
The material properties of fibre-reinforced thermoplastics are highly
dependent on the local fiber distribution and the markedness of anisotropy
can vary within a part. This study outlines a comprehensive test
programme for orthotropic plasticity and fracture behavior and how the local
anisotropy direction and degree obtained in the mould-injection process is
incorporated into the structural FE analysis.
VDI PIAE Plastics in Automotive Engeineering, Mannheim, 3–4 April 2019
Gese H, Oberhofer G, Brenner F, Richter M:
Comprehensive modeling of lightweight materials in crashworthiness simulation enables more reliable virtual development
This article provides an overview of the available modules to
describe metallic materials and non-reinforced and fiber-reinforced
plastics in the material model MF GenYld + CrachFEM. and it
presents example applications of various
materials in detail.
Enginesoft Newsletter, 4 / 2018, Winter 2018
Gese H, Oberhofer G, Richter M:
Modelling various light-weight materials in crash simulations
This survey of MF GenYld + CrachFEM presents the modules that can
describe deformation and failure for light-weight materials in
automotive designs and illustrates their application on boron
steels and fibre-reinforced thermoplasts.
Siegener Leichtbaukolloquium 2018
Gese H, Dell H, Reissner M, Brenner F:
Prediction of failure in sheet metal forming simulation – An integrated approach for shell and solid discretization
After outlining the general concept of the modular material model MF
GenYld + CrachFEM to predict material failure in sheet metals, this
lecture presents enhancements to the failure model with a focus on
sheet and solid meshes used in forming simulations.
Forming Technology Forum 2018, Zürich
Weiß-Borkowski N, Lian J, Camberg A, Tröster T, Münstermann S, Bleck W, Gese H, Richter H:
Forming Limit Curves of DP600 Determined in High-speed Nakajima Tests and Predicted by Two Different Strain-rate-sensitive Models
Measuring forming limit curves at high strain rates is costly.
Theoretical models are an alternative. This study compares
the results obtained from the numerical algorithm Crach and
the extended modified maximum force criterion with experimental
results. These two models were calibrated by the quasi-static
and dynamic uniaxial tensile tests and bulge tests of DP600.
ESAFORM 2018
Michalski M, Leicht U, Heath A, Merklein M:
Dynamic correction of oscillatory forces during ultrasonic-assisted metal forming
High-frequency oscillations that are superimposed on forming processes
can reduce the required forces, but a precise measurement of the
forming forces oscillating with high frequency is necessary. This
study introduces an approach to creating and employing a frequency
dependent force correction in the high dynamic range.
Production Engineering 11(2017)4–5, S. 455–465
Vogler M, Oberhofer G, Dell H:
Some Aspects on Characterizing and Modeling of Unreinforced and Short Fiber Reinforced Polymers in Crashworthiness Applications
The presentation introduces material modelling with
MF GenYld + CrachFEM and the underlying concept of parameter
characterization. Their application to unreinforced and short-fibre
reinforced polymers will be shown with a focus on strain localization
under tension and the ductile-brittle transition of failure.
Deutsches LS-Dyna Forum 2016, 10–12 October 2016
Gese H, Dell H, Reissner M, Heinle I, Wiegand K, Richter H, Lechner M, Hofmann M:
Experimental and theoretical investigations of shear band localization and shear fracture in advanced high strength steel sheets
Shear band localization is a frequent cause of shear fracture in
high-strength steels. The strain distribution during the onset of shear
band localization in a special shear specimen was measured optically.
The findings were incorporated into a tentative shear-band instability
module in MATFEM’s material model MF GenYld + CrachFEM.
Forming Technology Forum 2016, 12–13 September 2016, Ohlstadt, Germany
Vogler M, Dell H, Oberhofer G, Gese H:
Modelling non-reinforced, short-fibre reinforced and endless-fibre reinforced polymers in crash simulations
The material model MF GenYld + CrachFEM includes several
modules that can be used to model various classes of ploymers:
non-reinforced polymers; short-fibre reinforced polymers,
organic sheet and endless-fibre reinforced polymers with
unidirectional layers. These modules comprise modules
for anisotropic viscoelastic-plastic deformation and
anisotropic fracture. A modelling approach for non-orthotropic
unidirectional fibres is shown.
Kunststoffe und Simulation 2016, 26–27 April 2016
Brenner F, Gese H, Dell H, Oberhofer G, Metzmacher G:
Use of Specific Models for Creep, Plasticity and Fracture in Forming and Crashworthiness Simulation via UCREEP and VUMAT
When simulating various cold and thermal forming processes and
crash load cases of metals, all relevant aspects of the material’s
behavior such as creep, plasticity, hardening, fracture, strain-rate
and temperature dependency must be accounted for. Three examples are
presented in which forming behavior and failure prediction is
significantly improved by coupling specific user subroutines to
Abaqus / Standard or Abaqus / Explicit.
Deutsche SIMULIA-Konferenz, 12–13 Nov 2015, Aachen
Buckley M, Reissner M, Oberhofer G, Gese H:
Simulation of the manufacturing process of self-piercing rivets with LS-DYNA with focus on failure prediction for sheets and rivet
The manufacturing process of self-piercing rivets can be simulated
effectively by means of 2d-rotational symmetric elements with
r-adaptivity. The present work optimizes the numerical parameters
for such elements and employs the user material MF GenYld +
CrachFEM to assess the riveting process by means of a margin of safety
that considers the fracture of the top and bottom sheets as well as
fracture of the rivet itself when riveting aluminium and AHSS sheets
with limited ductility.
10th European LS-DYNA Conference, Würzburg, Germany
Gese H:
Failure Prediction of Quenched Boron Steels in Crashworthiness Simulation
Quenched boron steels are widely used for the passenger cab design,
especially for the A- and B-pillars. Components with tailored tempering
are used to adapt the material properties locally. The introduction of
those boron steels has brought some new challenges to the numerical
simulation. The material model MF GenYld + CrachFEM provides
comprehensive failure criteria for quenched boron steels. This includes
the prediction of localized necking, ductile normal fracture and ductile
shear fracture. It is possible to adapt the material properties locally
by mapping the hardness provided by the quenching simulation.
International CAE Conference 2014, Pacengo del Garda, Verona, 27–28
October 2014
Gese H, Dell H:
CrachFEM – A Comprehensive Approach for the Numerical Prediction of Instability And Fracture in Sheet Metal Forming Operations
CrachFEM includes a numerical model to predict tensile instability.
The advantage of that model over the classical FLC is that it
can determine the limit stresses transiently for non-linear strain
paths. The calibration by means of tensile tests reduces the
experimental effort and allows to predict the limit strain at
high strain-rates or high temperatures.
FLC Conference, 6–7 November 2014, IVP, ETH Zurich, Switzerland
Dell H, Yelisseyev V, Oberhofer G:
Failure prediction for non-reinforced and short fiber reinforced polymers
The specific behaviour of non-reinforced and short-fiber reinforced
polymers in crash or drop test load cases imposes special
demands on the material model as well as the experimental determination
of material parameters. A robust phenomenological approach is shown.
13th LS-Dyna Forum 2014, Bamberg, 6–8 October 2014
Entelmann W, Stelling R, Brenner F, Metzmacher G, Gese H:
Relaxation Forming of Double Curved Fuselage Panels – Assessment of Formability And Optimization of Process Parameters With Numerical Analysis
Room-temperature stretch forming is the state-of-the-art technology for
manufacturing doubly curved fuselage panels of aeroplanes. A new
generation of AlMgSc alloys that are stable up to temperatures beyond
300 °C opens up a the possibility of a hot forming process
with subsequent stress relaxation. This study describes challenges in
simulating the process in order to find good process parameters that
minimize springback. The FEA code ABAQUS / Standard was used with a
user-defined temperature-dependent material model with orthotropic
plasticity and orthotropic creep.
7th Forming Technology Forum Warm and Hot Forming,
15–16 September 2014 Enschede, the Netherlands
Heath A, Gese H, Oberhofer G, Dell H:
Modeling Failure for Nonlinear Strain Paths With CrachFEM
This paper describes a general technique for simulating sheet failure
under complex deformation. Separate failure risks are calculated for
unstable necking and ductile fracture modes associated with void growth
and shear banding. Necking is detected by a multi-scale method that
considers sheet inhomogeneity, strain hardening, Bauschinger effects,
strain rate sensitivity and the multi-axial stress-state in the neck.
The failure methodology is implemented in the software module
MF GenYld + CrachFEM, which can be coupled to all major explicit
FEM codes.
Numisheet 2014, Melbourne, Australia
Gese H, Oberhofer G, Oehm M, Heath A:
CrachFEM – A Comprehensive Approach for the Prediction of Sheet Failure in Multi-Step Forming and Subsequent Forming and Crash Simulations
Industrial sheet metal forming simulations predict a possible sheet
failure mainly by means of the forming limit diagram (FLC), a criterion
based on the onset of localized necking and valid only for linear strain
paths. The FLC cannot be used in multistep forming simulations, in
subsequent forming and crash simulations or for AHSS, UHSS and aluminium
sheets, where fracture can occur without prior necking. MF GenYld +
CrachFEM offers a comprehensive approach to predict material failure in
sheet metals that overcomes these limitations.
Forming Technology Forum 2013, 19–20 September, 2013,
Herrsching, Germany
Brenner F, Buckley M, Gese H, Oberhofer G:
Influence of Discretisation on Stiffness and Failure Prediction in Crashworthiness Simulation of Automotive High-Pressure Die Cast Components
Castings are widely used as part of the car chassis because of their
light weight and the flexibility of their design. The comparably
low ductility of castings requires dependable crash simulations, but
modelling casting parts correctly for finite-element analyses is an
issue for several reasons. This study describes the challenges when
modelling cast alloys as quasi-homogeneous and provides a benchmark of
an enxample alloy modelled with different element types at various mesh
sizes.
9th European LS-DYNA Users’ Conference, Manchester, 2–4 June 2013
Reißner M, van der Veen S, Groß M, Gese H:
Prediction of plane stress fracture toughness for aluminium sheet materials with numerical methods
The aim of the presented work is to determine the thickness dependence
of plane-stress fracture toughness by means of finite-element
simulations. C(T) 127 specimens of three different aluminium alloys
with five different sheet thicknesses from 0.8mm to 3.2mm each were
simulated with MF GenYld + CrachFEM with a very fine solid mesh.
ESIS-Workshop on Computational and Experimental Failure Mechanics,
14–15 June 2012, BAM Berlin, Germany
Gese H, Dell H:
Contribution of improved material models to the virtual assessment of the process robustness of sheet forming processes
This paper focuses on extended criteria for the prediction of sheet
failure. In addition to the deterministic prediction of a failure risk,
a failure probability can be derived from the scatter of one material
batch. An implementation of a model for failure probability is discussed
in detail. A stochastic approach can be used on top to account for the
influence of the scatter between consecutive material batches.
Forming Technology Forum 2011, 17–18 May 2011,
IVP, ETH Zurich, Switzerland
Weiss U, Bach A:
A Contribution of Advanced Material Models for Numerical Simulation of Lightweight Components
Magnesium castings offer significant weight saving potential for many
crash-relevant structures in the vehicle. Until now, proper cast
magnesium design was difficult and time consuming, as reliable CAE
tools were not available. In the European funded research project
NADIA, a new set of CAE tools have been developed for AM60 and AM50
alloys that combine local casting process simulation results with crash
failure CAE modelling to reliably predict component level crash
behaviour. These CAE tools have been made commercially available and
integrated into existing CAD / CAE codes.
La Metallurgia Italiana – n. 11–12 / 2011
Buckley M, Selig M, Oehm M:
A new method for CrachFEM damage parameter calculation and transfer from Autoform to LS-Dyna
Many industrial forming simulations are done with the implicit
finite-element code Autoform. Subsequent crash analyses should
incorporate information from the forming process, but the regular
finite-element data exported by Autoform is missing crucial data
such as orthotropy and damage parameters. MATFEM and Autoform have
developed a method to obtain accumulated failure risks and a risk
against localized necking from Autoform simulations in a
post-processing step and to incorporate these into crash simulations.
The present study compares results of this method with results
from the same process simulated with LS-Dyna throughout.
8th European LS-DYNA Users Conference,
23–24 May 2011, Strasbourg
Gese H:
Advanced prediction of material failure in metal forming and crash simulation with material model MF GenYld + CrachFEM
The material model MF GenYld + CrachFEM has been developed for an
advanced prediction of failure and defromation. This presentaton
outlines failure prediction in three applications: in the process chain
of deep drawing and crash of steel sheets; for aluminium and magnesium
extrusions in crash and for magnesium high-pressure die castings in
crash.
Enginsoft International Conference 2010,
21 October, Fiera Montichiari, Italy
Lange C, Bron F, Hänggi P, Möller T, Gese H, Daniel D, Leppin C:
Forming simulation of aluminum car body sheet with different yield models and comparison with experiments
In recent years, significant effort has been invested in improving the
accuracy of the formability assessment of aluminum car body panels by
numerical deep drawing simulations. Adequate modeling of the plastic
deformation of the sheet and the friction between sheet and tools are
both crucial for correct predictions of the final thickness and
fracture. In this paper, the constitutive yield models Barlat 2000,
Bron-Besson 2004 and Hill 1948 are investigated for the AA6016 T4
aluminum alloy car body sheet DR100.
IDDRG 2010, Graz, 31 May–2 June 2010
Oberhofer G, Gese H, Oehm M:
Modelling Non-Reinforced and Fiber-Reinforced Polymers with Material Model MF GenYld + CrachFEM
The material model MF GenYld + CrachFEM can model non-reinforced and
short fibre-reinforced polymers in crash simulations with a modular
approach. Anisotropic hardening can be combined with an elastic and
plastic orthotropy for fibre reinforced polymers. The plastic orthotropy
can be different for tension and compression. This model for
elasto-plastic behaviour is complemented by models to predict the onset
of material failure due to ductile normal fracture and ductile shear
fracture.
Automotive CAE Grand Challenge 2010" Hanau, 30–31 March 2010
Gese H, Oberhofer G, Oehm M:
Crash Simulation with Material Model MF GenYld + CrachFEM based on Results of Process Simulation
The material model MF GenYld + CrachFEM can be used in
multi-trade simulations to evaluate the crashworthiness of components.
Multi-trade simulations are analyses of linked physical phenomena where
the results of an analysis are incorporated into subsequent simulations.
Examples in this lecture include mapping from deep-drawing to crash;
properties from processing and joining of sheet metals and local
properties of die-cast components.
Automotive CAE Grand Challenge 2010 Hanau, 30–31 March 2010
Gese H, Klamser H, Stolfig P, Groß M, Meyer L W, Abdel-Malek S:
An improved material model for the assessment of crash performance of magnesium extrusions
Magnesium extrusion profiles offer a good potential for weight
reduction in vehicle components. The designer of such components
must consider the particularities of megnesium profiles: Non-linear
elastic hebaviour, marked plastic orthotropy and anisotropic hardening.
The present work outlies the design process of a bumper made of a
two-chambered profile made from the Mg alloy MnE21. The simulation
used LS-Dyna with the user material model MF GenYld + CrachFEM,
which can account for all effects listed above.
Nordmetall-Kolloquium 2–3 December 2009, Adorf near Chemnitz
Gese H, Dell H, Obehofer G:
Models for Isotropic-Kinematic Hardening and Anisotropic Hardening in Material Model MF Genyld + Crachfem
This presentation presents the available models for anisotropic
hardening and isotropic-kinematic hardening in the modular material and
failure model MF GenYld + CrachFEM. It is also shown how the inclusion
of isotropic-kinematic hardening leads to a better prediction of tensile
instability with CrachFEM.
Forming Technology Forum 2009,
5–6 May 2009, IVP, ETH Zurich, Switzerland
Dell H, Gese H, Oberhofer G:
Advanced Yield Loci and Anisotropic Hardening in the Material Model MF GenYld + CrachFEM
This paper highlights some extended features of the plasticity model
MF GenYld. Superposition of two base yield loci can model the
material behaviour of some textured sheet materials. A new orthotropic
yield locus (Dell 2006) allows to model materials with a low yield
strength in shear but elliptical locus in the tension-tension regime for
both plane-stress and general three-dimensional stress conditions. Yield
locus modification allows to reach a better representation of the
deformation by means of factors to scale the locus in a defined stress
regime. Anisotropic hardening makes these factors dependent on the
plastic strain. It can model the behaviour of materials like stable
austenitic steel sheets or magnesium sheets.
Numisheet 2008, 1–5 September 2008, Interlaken, Switzerland
Kessler L, Gese H, Metzmacher G, Werner H:
An approach to model sheet failure after onset of localized necking in industrial high-strength steel stamping and crash simulations
It is well known that after the onset of a local instability
additional strain is necessary to induce fracture. In a numerical
simulation with shell elements this post-instability strain is
more important in elements with small edge lengths as they are
used increasingly in industrial applications today. The enhanced
necking model combines the model for localized necking with the
model for ductile shear fracture. Results for three steel grades
and for various mesh sizes are shown and compared to Nakajima
tests.
2008 SAE World Congress.
14–17 April 2008, Cobo Center, Detroit, Michigan, USA
Lanzerath H, Bach A, Oberhofer G, Gese H:
Failure prediction of Boron steels in crash
Hot-formed steels offer a great weight saving potential over
conventional cold-formed steels in crash relevant structural parts,
because of their enormous strength and the very good
dimensional control – there is nearly no springback. The quench
hardening process causes a significant reduction of the material
ductility, however. The prediction of the deformation and fracture
behavior is one of the major interests during the vehicle development
process. The paper will give an overview on material properties of Boron
steels and outline a suitable failure modeling approach for crash
simulation.
2007 SAE World Congress.
16–19 April 2007, Cobo Center, Detroit, Michigan, USA
Dell H, Gese H, Oberhofer G:
CrachFEM – A Comprehensive Approach for the Prediction of Sheet Metal Failure
Forming limit curves (FLC) are the industry’s standard approach to
assessing failure in metal sheets. That concept is limited to linear
strain paths, however. The algorithm Crach can predict localized necking
for arbitrary strain paths. High-strength steels and aluminium
sheets can also be subject to ductile fracture without prior
localized necking. The relevant types of fracture for sheet metals are
ductile fracture caused by microvoids and shear fracture caused by shear
band localization. The comprehensive fracture model CrachFEM
can account for those modes.
NUMIFORM ’07, Materials Processing and Design:
Modeling, Simulation and Applications, 18–21 June 2007
Leppin C, Daniel D, Shahani R, Gese H, Dell H:
Formability Prediction of Aluminum Sheet in Automotive Applications
The AA6016 T4 aluminum alloy car body sheet DR100
is characterized with a comprehensive
experimental programme for orthotopic elastoplastic
deformation behavior as well as the failure modes
localized necking, ductile fracture and shear fracture.
The results are validated with MF GenYld + CrachFEM
in deep drawing with a cross-shaped punch modelled with shells
and a simplified hemming process modelled with solid elements.
NUMIFORM ’07, Materials Processing and Design:
Modeling, Simulation and Applications, 18–21 June 2007
Oberhofer G, Franzen M, Dell H:
Modelling of Non-Reinforced Polymeric Material Behaviour in the Explicit FEM Method for Crash Simulation
MATFEM has developed the material model
MF GenYld which can model different hardening behaviour
in tension, compression, shear and biaxial loading, as
well as the high degree to which the hardening
behaviour depends on the strain rate. This material
model has been coupled with CrachFEM for taking into
account the influence of loading condition and strain
rate on the fracture prediction. In a research
project, Ford Forschungszentrum Aachen GmbH and MATFEM
validated the material model for non-reinforced polymers
in automotive applications. The experiments,
the process of material data processing and first
validation results are shown.
Kunststoffe + Simulation, 13–14 June 2007,
Fellbach / Stuttgart
Oberhofer G, Gese H, Groß M, Kühling M, Seidel D:
Numerical Analysis of the Balloon Dilatation Process Using the Explicit Finite Element Method for the Optimization of a Stent Geometry
Endovascular stent surgery is a minimally invasive
surgical procedure to treat disorders of the
circulatory system. Nearly all of the medium-sized
and large blood vessels in the body’s vascular system
can be accessed by a balloon catheter system. New stent
materials and geometries can be assessed with explicit
finite-element simulations. MF GenYld + CrachFEM was
used to simulate crimping, balloon dilatation and recoil
of the stent, because it can model the Bauschinger
effect and stress-state dependent fracture.
LS-Dyna Forum 2006, 12.−13. Oktober 2005, Ulm
Gese H, Dell H:
Numerical Prediction of FLC with the Program Crach
The numerical algorithm Crach can predict localized
necking in sheet metal. It is based on an instability
model with an initial imperfection with a finite
dimension. Crach uses a comprehensive material model
which includes all relevant effects such as plastic
orthotropy, combined isotropic-kinematic hardening and
strain rate sensitivity. Therefore, Crach can be applied
to a wide variety of materials and boundary conditions,
e.g. necking during hot forming or necking at high strain
rates. Crach’s strength is the prediction of necking for
nonlinear strain paths.
FLC Zürich, 15–16 March 2006, IVP,
ETH Zürich, Switzerland
Kessler L, Beier Th, Werner H, Horstkott D, Dell H, Gese H:
Material Selection for an Ultra High Strength Steel Component Based on the Failure Criteria of CrachFEM
An increasing use of combining more than one process
step is noticed for coupling crash simulations with the
results of forming operations – mostly by inheriting
the forming history of plastic strain and material
hardening. Introducing a continuous failure model
allows a further benefit of these coupling processes;
it sometimes can even be the most attractive result of
such a work. In this paper the algorithm CrachFEM for
fracture prediction has been used to generate more
benefit of the successive forming and crash simulations
– especially for ultra high strength steels. The choice
and selection of the material grade in combination with
the component design can therefore be done far before
the prototyping might show an unsuccessful crash
result; and in an industrial applicable manner.
6th Numisheet Conference 2005,
"On the Cutting Edge of Technology"
August 15–19, 2005, Detrit, Michigan, U.S.A.
Hooputra H, Gese H, Dell H, Werner H:
A Comprehensive Failure Model for Crashworthiness Simulation of Aluminium Extrusions
A correct representation of the plastic deformation and failure of
individual component parts is essential to accurate crashworthiness
simulations. This paper presents a comprehensive approach for predicting
failure in components based on macroscopic strains and stresses. That
approach requires the representation of a number of different failure
mechanisms, such as necking due to local instabilities as well as
ductile and shear fracture. All failure criteria can represent the
influence of non-linear strain paths. Simulation results of
three-point bending and axial compression tests of double chamber
extrusion components made of an EN AW–7108 T6 aluminium alloy are
compared to test results.
International Journal of Crashworthiness, Vol. 9, No.5,
Woodhead Publishing (2004), pp. 449–463.
Werner H, Dell H, Metzmacher G, Kessler L, Heath A:
Methodology, Validation and Application of a Failure Model Based on Transient Forming Limit Curves for Coupled Stamping and Crash Processes as Part of the IMPACT Project
Predicting the failure of structural components in a crash event is one
of the major challenges of numerical simulations in the automotive
industry. In the IMPACT project, a numerical model to enhance the
failure prediction was developed and applied to selected high-strength
sheet steel materials typically used in the body in white. The presented
failure model is based on the transient prediction of localized necking
in sheets and takes into account the forming history of the components.
To validate the model, two- step forming processes have been carried out
on a laboratory scale experimentally as well as numerically.
Europam 2003, 16–17 October 2003, Mainz, Germany
Schmid M, Claus J, Gese H, Löhe D:
Thermal fatigue component test of engine parts
In this study, the effect of thermal fatigue on pistons and cylinder
heads is investigated. A test method with realistic heating and cooling
conditions is presented. To get information about the constraints at
critical regions of the investigated engine components, fiber optic
strain and temperature gauges are used. The ratio of measured total
strain and thermal strain gives information on proportion of thermal
strain being obstructed. The thermal fatigue piston test is simulated
with FE methods. The results of experimental and simulated life times
are compared.
International Congress Thermal Stresses ICTS 2003, 8–11 June 2003,
Blacksburg, Virgina, USA
Gese H, Dell H, Keller S, Yeliseyev V:
Measuring flow curves of metal sheets at high strains for forming simulations
Sheet forming processes such as deep-drawing or hydroforming can lead to
very high local deformations. Simulations of these processes must be
able to model these large strains. The typical means to obtain flow
curves at high stresses is to extrapolate the flow curve measured in
unixial tension tests. Since this method can lead to large errors,
three alternative experiments are presented and assessed for an
aluminium alloy: in-plane torison tests, hydraulic bulge tests and
layered stack compression tests can measure flow curves for high strains
more reliably.
DVM-Tagung "Werkstoffprüfung 2002 – Kennwertermittlung für
die Praxis", 5–6 December 2002, Bad Nauheim
Werner H, Gese H:
On the significance of strain-rate dependent material properties in crash simulations
Crash simulation aims to assess and improve car designs in order to
protect passengers and pedestrians. Since characteristic time
spans of deformations during crashes are in the range of milliseconds,
the material behaviour at high deformation velocities must be known.
This study is about the influence of deformation speed on the material
behaviour. Experiments must be carried out at typical deformation speeds
during crash scenarios. This work shows suitable experiments to
determine strain-rate dependent flow curves and strain-rate dependent
fracture.
DVM-Tagung "Werkstoffprüfung 2002 – Kennwertermittlung für
die Praxis", 5–6 December 2002, Bad Nauheim
Dell H, Gese H, Keßler L, Werner H, Hooputra H:
Continuous failure Prediction Model for Nonlinear Load Paths in Successive Stamping and Crash Processes
The validity of numerical simulations is still limited by the unknown
failure of materials when nonlinear load paths in successive stamping
and crash processes occur. Localized necking is the main mechanism for
fractures in ductile sheet metal. The classical forming limit curve
(FLC) is limited to linear strain paths. A new algorithm on the basis
of the Marciniak model, Crach, can include the effects of nonlinear
strain paths. It is calibrated and validated with a set of multi-stage
experiments under static and dynamic strain rates for a mild steel.
SAE Technical Paper Series 2001–01–1131
Gese H, Beck W, Reese E D:
Stretch Forming of Aluminium Sheets
Daimler-Benz Aerospace Airbus GmbH produces large aircraft skin panels
with doubly curved geometry from Al-alloys on a stretch forming press.
The alloy, heat treatment and the press kinematics can be modified to
improve the manufacturing process of a given skin panel. These
modifications can be assessed by means of numerical methods. Here, the
finite element code PAM-Stamp is used for the simulation of the stretch
forming process and springback. The aluminium alloys were modelled with
PAM-Stamp’s material 109. Dedicated software can determine the optimal
press kinematics and convert them to boundary conditions for the
simulation. The presentation includes benchmark problems for actual
parts with single- and two-step forming, trimmimg and springback.
PAM ’97, 16–17 October 1997, Prague, Czech Republic