Zeitschriftenartikel
  • D. Colin
  • S. Bel
  • T. Hans
  • Mathias Hartmann
  • K. Drechsler
Virtual Description of Non-Crimp Fabrics at the Scale of Filaments Including Orientation Variability in the Fibrous Layers, vol. 27, pg. 337-355.

In: Applied Composite Materials

  • 2020

DOI: 10.1007/s10443-020-09819-1

A numerical description of dry non-crimp fabrics is proposed at the scale of the filaments using a commercially available finite element software package. Deviations in the filament orientation of the fibrous layer is a dominant factor in the occurrence of local defects, which influences the mechanical response of the textile. Therefore, the introduction of variability in the orientation distribution is proposed in this paper. This approach enables to capture the entanglement of the filaments and models all interaction mechanisms. A stepwise generation of the numerical non-crimp fabric is proposed considering the main manufacturing steps to reproduce the local defects in the fibrous mat appropriately. Averaged periodic boundary conditions are developed ensuring an overall periodicity of the model while allowing reorientation at the scale of the filaments. Two various non-crimp fabrics are investigated and modelled. The distribution of the filaments in the simulation results correlate well with measurements of the filament orientation performed on the textiles. Moreover, a detailed comparison of the local defects shows a good agreement with measurements on the specimens. The presented approach can be used to generate geometries for subsequent virtual characterization.
  • TC Hutthurm
  • NACHHALTIG
Vortrag
  • Mathias Hartmann
Composites forming – from manual prepreg layup to modeling integrated process control, a continuing quest. Keynote presentation

In: 22nd International Conference on Material Forming (ESAFORM 2019)

  • 2019
  • TC Hutthurm
  • NACHHALTIG
Vortrag
  • D. Bublitz
  • M. Angstl
  • Mathias Hartmann
  • K. Drechsler
Implementation of a viscoelastic material model to pre-dict the compaction response of dry carbon fiber preforms

In: 30th SICOMP Conference - Manufacturing and Design of Composites

  • 2019
  • TC Hutthurm
  • NACHHALTIG
Vortrag
  • D. Colin
  • S. Bel
  • T. Hans
  • Mathias Hartmann
Numerical Description of Multiaxial Non-Crimp Fabrics at Refined Scale

In: Euromech Colloquium 602 – Composite manufacturing processes. Analyses, modelling and simulations

  • 2019
  • TC Hutthurm
  • NACHHALTIG
Beitrag (Sammelband oder Tagungsband)
  • D. Colin
  • S. Bel
  • T. Hans
  • Mathias Hartmann
Virtual description of a biaxial 0°/90° non-crimp fabric with normally distributed filament directions, pg. 020009.

In: Proceedings of the 22nd International Conference on Material Forming (ESAFORM 2019). null (AIP conference proceedings)

  • 2019

DOI: 10.1063/1.5112514

This study aims at predicting the mechanical behavior of a 0°/90° biaxial tricot-chain NCF using digital chain elements. In order to reproduce the entanglements of the filaments and their deviation from the ideal 0°/90° paths, the orientation of the digital chains is sampled with a normal distribution. This enables an accurate reproduction of the geometrical deviations observed on the material. Moreover, averaged periodic boundary conditions have been developed to apply an overall mesoscopic periodic deformation to a model that doesn’t exhibit any periodicity at the scale of the digital chains. These models have subsequently been used for virtual characterization of the compaction behavior and were compared to experimental results. It is shown that the resulting thickness and compaction stiffness are very sensitive with respect to the distribution used to sample the chain’s directions. Moreover, the smallest representative volume element (RVE) compliant with the mesoscopic periodicity is already able to capture the defects and the compaction behavior with reduced computation time.
  • TC Hutthurm
  • NACHHALTIG
Beitrag (Sammelband oder Tagungsband)
  • S. Venkat
  • Mathias Hartmann
Virtual test bench to characterize load bearing behavior of laminates with out-of-plane ply deflections and localized wrinkles
  • 2018
  • TC Hutthurm
  • NACHHALTIG
Zeitschriftenartikel
  • M. Lipcan
  • J. Balvers
  • Mathias Hartmann
Thermal response of frame-like composite structures to analytically assess manufacturing distortion, vol. 107, pg. 399-408.

In: Composites Part A: Applied Science and Manufacturing

  • 2018

DOI: 10.1016/j.compositesa.2018.01.012

The proposed approach assesses frame-like composite parts prone to distortion without needing a full-scale finite element simulation. These structures are reduced to a series of constant cross-sections and curvatures. A simplified shape response of each thin-walled composite cross-section during curing is analytically obtained by employing homogenization methods at different geometrical levels. This includes a novel approximation method for the mechanical properties of a T-section including a gusset filler. The model is validated against a currently deployed finite element approach. A good agreement is reached for the thermal response of a gusset and a cross-section, whereas for an extruded frame-like structure, the analytically calculated deformation is about 20% higher than the simulated one. The cause is identified and solutions are proposed. Nevertheless, knowing its limitation, the ease of use together with the high potential for automation makes this altogether a possible method for predicting process-induced deformation in the early design phase.
  • TC Hutthurm
  • NACHHALTIG
Beitrag (Sammelband oder Tagungsband)
  • D. Colin
  • S. Bel
  • T. Hans
  • Mathias Hartmann
Towards a virtual characterization of a biaxial non-crimp fabric
  • 2018
  • TC Hutthurm
  • NACHHALTIG
Beitrag (Sammelband oder Tagungsband)
  • M. Lipcan
  • J. Balvers
  • Mathias Hartmann
A strategy for cost-effective compensation of process induced deformations in composite structures
  • 2018
  • TC Hutthurm
  • NACHHALTIG
Beitrag (Sammelband oder Tagungsband)
  • D. Colin
  • S. Bel
  • T. Hans
  • Mathias Hartmann
On the inter-stitch interaction in biaxial non-crimp fabrics, pg. 020004.

In: Proceedings of the 21st International ESAFORM Conference on Material Forming (ESAFORM 2018). null (AIP conference proceedings)

  • 2018

DOI: 10.1063/1.5034805

Simulation models of fiber reinforcements at the scale of fibers possibly reproduce important deformation mechanisms and can offer predictive capabilities on the macroscopic mechanical behavior. Although potential deformation mechanisms are already listed in the literature, these phenomena should be experimentally investigated to evaluate their relevance in simulation at the scale of fibers. This study focuses on the inter-stitch interaction of Non-Crimp Fabric (NCF) and aims at quantifying the relative motion of the stitching yarns. To this end, controlled shear deformation was introduced on +/-45° biaxial tricot stitched NCF. The stitching yarns have been colored on the backside of the sample while the front face remained uncolored. Therefore, an inter-stitch relative motion can be observed if an uncolored portion of the stitching yarn appears on the back face of the sample. The samples were observed during the experiments with a digital microscope in order to measure the uncolored portion of the yarns on the back face. Thus, the stitching yarn movement can be quantified for various shear angles. A significant relative motion was observed compared to the original stitching length. Based on this study, the authors argue that the inter-stitch sliding is a relevant deformation mechanism for biaxial tricot stitched NCF at the scale of fibers.
  • TC Hutthurm
  • NACHHALTIG
Vortrag
  • S. Zaremba
  • A. Carrels
  • Mathias Hartmann
Modellierung von Race Tracking in der Füllsimulation und numerische Untersuchung zur Makroporenentwicklung im RTM-Prozess

In: ESI Forum in Deutschland

  • 2017
  • TC Hutthurm
  • NACHHALTIG
Zeitschriftenartikel
  • R. Taubert
  • U. Mandel
  • Mathias Hartmann
Influence of nonlinear material behavior on the effect of inter-fiber cracks in composite laminates, vol. 51, pg. 3819-3833.

In: Journal of Composite Materials

  • 2017

DOI: 10.1177/0021998317694372

This paper presents a numerical study evaluating the influence of nonlinear material behavior on the stiffness reduction due to inter-fiber cracks. It is shown that the relation between crack density and damage variables changes as the load level increases. A three-dimensional nonlinear material model is used in a representative volume element study to accurately calculate the local stress distribution around cracks. The studies show that as the load increases the stress recovers to the far-field level within a shorter distance, and consequently the plastic deformation causes a decrease in the crack-induced stiffness reduction. To provide damage variables for a coupled elastoplastic-damage material approach at the homogenized ply level, the results of a systematic representative volume element study are used for interpolation. For verification, the response curves of several laminates influenced by inter-fiber cracks are simulated and compared to experimental results. The presented procedure enables the constitutive laminate response under large deformations to be accurately predicted.
  • TC Hutthurm
  • NACHHALTIG
Beitrag (Sammelband oder Tagungsband)
  • D. Hartung
  • Mathias Hartmann
Validation and industrial implementation of an analysis method for predicting deformations induced by the composite curing process
  • 2017
  • TC Hutthurm
  • NACHHALTIG
Hochschulschrift
  • Mathias Hartmann
Analysis and Compensation of Process Induced Deformations in Composite Structures
  • 2017
Aerospace structures are designed to tight dimensional tolerances in order to ensure ease of fit during assembly. Geometrical deviations of the part “as built” from the nominal tooling inherently arising from the manufacturing process of carbon fiber reinforced plastics can pose a significant risk to production through unexpected delays and rework cost. Process analysis and modeling of relevant mechanisms inducing part distortion can be used to alleviate the risk. This book contributes a framework for guiding the analysis engineer in choosing appropriate modeling tools and the respective level of detail for the assessment of process induced deformations (PID) on a given use case.
  • TC Hutthurm
  • NACHHALTIG
Vortrag
  • Mathias Hartmann
Analysis and Compensation of Process Induced Deformations in Composite Structures

In: CCeV-Arbeitsgruppentreffen „Engineering“

  • 2017
  • TC Hutthurm
  • NACHHALTIG
Beitrag (Sammelband oder Tagungsband)
  • M. Copony
  • Mathias Hartmann
Towards a simulation strategy to predict laminate quality and porosity for partially impregnated CFRP prepregs
  • 2017
Out-of-autoclave (OoA) prepregs produce low-porosity parts through a complex consolidation process that includes air evacuation through a partially impregnated microstructure and subsequent resin infiltration flow. For their successful industrial application, the void content has to be restricted to that of benchmark autoclave structures. A detailed understanding and an optimal selection of processing parameters is required to compensate the reduced consolidation pressure in OoA processing especially for complex structures. Capturing void formation phenomena by simulations is the solution of interest to avoid expensive and protracted testing. In this paper a simulation strategy is proposed which captures the relevant phenomena affecting porosity development. The goal is a coupled FE simulation including air and volatile evacuation, resin flow, fiber bed compaction, mechanical behavior including frictional behavior, and the thermal management. These phenomena have partly strong interdependencies between each other which need to be considered. The output of the proposed FE simulation is the spatial distribution of residual porosity, final thickness and fiber volume contents of parts produced from OoA, enabling an optimized process and part design to gain void free structures.
  • TC Hutthurm
  • NACHHALTIG
Vortrag
  • Mathias Hartmann
Manufacturing Process Simulation at the LCC

In: CCeV-Arbeitsgruppentreffen „Herstellprozess-Simulation“

  • 2016
  • TC Hutthurm
  • NACHHALTIG
Zeitschriftenartikel
  • J. Weiland
  • Mathias Hartmann
  • R. Hinterhölzl
Cure simulation with resistively in situ heated CFRP molds: Implementation and validation, vol. 80, pg. 171-181.

In: Composites Part A: Applied Science and Manufacturing

  • 2016

DOI: 10.1016/j.compositesa.2015.10.020

In composite processing of parts with varying cross-sections, homogeneous cure is sought but poses a significant challenge. Electrically heated molds for resin transfer molding (RTM) processes offer the potential to locally introduce heat and, thus, achieve more homogeneous cure and enhanced part quality. However, low conductivity of CFRP poses a risk of uncontrolled exothermic reactions. To target this potential, an appropriate and efficient numerical method is presented in this study to simulate part cure governed by resistive heated CFRP molds. A numerical control algorithm for 3D finite element cure simulations is developed, which uses the reaction flux of a temperature boundary condition to calculate the arising tool temperature field. The capability of this method to predict non-uniform tool temperatures of self-heated CFRP molds with close to thermocouple accuracy during the cure process is shown by means of numerical verification and experimental validation on a self-heated CFRP plate.
  • TC Hutthurm
  • NACHHALTIG
Beitrag (Sammelband oder Tagungsband)
  • R. Helmus
  • M. Copony
  • Mathias Hartmann
  • P. Hubert
  • R. Hinterhölzl
Modelling void formation in corners during out-of-autoclave prepreg processing
  • 2016
  • TC Hutthurm
  • NACHHALTIG
Beitrag (Sammelband oder Tagungsband)
  • J. Weiland
  • Mathias Hartmann
  • R. Hinterhölzl
Characterization and numerical investigation of an RTM cure process with CFRP molds and independent heat patches
  • 2015
The knowledge of the temperature development within thick carbon fiber reinforced polymer (CFRP) parts during cure is crucial for the production of high performance aerospace components given that high exothermic temperature peaks may degrade material properties and introduce additional components of residual stress. During cure of CFRP parts with complex geometry and varying cross sections a uniform temperature distribution and hence homogenous material property development is sought. A novel resin transfer molding (RTM) tooling concept, consisting of CFRP mold parts with integrated in situ heating patches, is modelled within a commercial finite element platform (Abaqus) for further cure simulation utilizing Compro/CCA. A mono-component resin system and the tooling material were characterized by means of differential scanning calorimetry (DSC) and NanoFlashTM tests. Characterized material data was verified by simulative prediction and experimental comparison of a 30 mm laminate coupon during cure. A simulation strategy was developed and implemented to model the transient thermal response of the in situ heating device by modification of boundary conditions via a feedback control system. Finally a typical process temperature cycle has been used to validate the implemented simulation strategy numerically.
  • TC Hutthurm
  • NACHHALTIG
Vortrag
  • Mathias Hartmann
  • D. Hartung
  • R. Hinterhölzl
Applicability and effectiveness of simple to detailed methods for spring-in and warpage quantification: a case study

In: ICMAC 2015 Conference

  • 2015
  • TC Hutthurm
  • NACHHALTIG
Beitrag (Sammelband oder Tagungsband)
  • Mathias Hartmann
  • R. Hinterhölzl
Process induced deformations – A study on sandwich test samples
  • 2014
  • TC Hutthurm
  • NACHHALTIG
Vortrag
  • Mathias Hartmann
Simulation of process induced deformations (spring-back) - Simple Methods for Strain Anisotropy Evaluation on a Generic I-Profile Frame Structure.

In: Symposium on the occasion of the 5th anniversary of the Institute for Carbon Composites

  • 2014
  • TC Hutthurm
  • NACHHALTIG
Beitrag (Sammelband oder Tagungsband)
  • Mathias Hartmann
  • M. Strebinger
  • R. Hinterhölzl
An approach towards a basic materials characterization for the simulation of process induced deformations
  • 2013
  • TC Hutthurm
  • NACHHALTIG
Vortrag
  • Mathias Hartmann
Aushärtesimulation – Grundlagen, Charakterisierung und Anwendung

In: CCeV-Arbeitsgruppentreffen „Herstellprozess-Simulation“

  • 2013
  • TC Hutthurm
  • NACHHALTIG
Zeitschriftenartikel
  • D. Heim
  • Mathias Hartmann
  • J. Neumayer
  • C. Klotz
  • Ö. Ahmet-Tsaous
  • S. Zaremba
  • K. Drechsler
Novel method for determination of critical fiber length in short fiber carbon/carbon composites by double lap joint, vol. 54, pg. 365-370.

In: Composites Part B: Engineering

  • 2013

DOI: 10.1016/j.compositesb.2013.05.026

A novel approach is introduced for the experimental determination of critical fiber length in carbon fiber reinforced carbon (CFRC) composites. Critical fiber length is investigated using double lap joint samples. The transition of failure mode from bonding failure to fiber fraction with increasing overlap length correlates with the critical fiber length. Tested overlap lengths were in the range of 4–100 mm. For CFRC at hand, failure mode changes at an overlap length of 26 ± 2 mm. Hence critical fiber length is derived as lc = 52 ± 4 mm.
  • TC Hutthurm
  • NACHHALTIG
Vortrag
  • Mathias Hartmann
  • R. Hinterhölzl
  • K. Drechsler
Fertigungsbedingter Verzug von CFK-Bauteilen: Einflussfaktoren und Methoden zur „a priori“ Bewertung.

In: EADS Gesprächsrunde Tooling für die CFK-Produktion

  • 2013
  • TC Hutthurm
  • NACHHALTIG
Vortrag
  • Mathias Hartmann
  • G. Fernlund
Assessing Warpage in Composites Manufacturing: In Search of a Simple Solution to a Complex Problem

In: 6th International Symposium on Manufacturing Technology for Composite Aircraft Structures (ISCM)

  • 2012
  • TC Hutthurm
  • NACHHALTIG
Vortrag
  • Mathias Hartmann
  • M. Brand
  • A. Kollmannsberger
Anwendung der CATIA V5-Module im Design-Prozess von Faserverbundbauteilen

In: Transcat: Eröffnungsfeier

  • 2012
  • TC Hutthurm
  • NACHHALTIG
Vortrag
  • Mathias Hartmann
  • R. Hinterhölzl
Prediction of Process Induced Deformations Like Spring-In

In: ESAComp Users’ Meeting

  • 2011
  • TC Hutthurm
  • NACHHALTIG