Roland Hinterhoelzl

Fachhochschule Oberösterreich | fh-ooe · School of Engineering

Out-of-plane fiber waviness, also referred to as wrinkling, is considered one of the most significant effects that occur in composite materials. It significantly affects mechanical properties, such as stiffness, strength and fatigue and, therefore, dramatically reduces the load carrying capacity of the material. Fiber waviness is inherent to variou...

Out-of-plane fiber waviness is a common effect inherent to various manufacturing processes of fiber-reinforced composite parts. They cannot be completely avoided and therefore have to be tolerated and be considered as an inherent part of the structure. To this point, there is still no acceptable approach in aircraft industry to quantitatively suppo...

The limited capability to predict material failure in composite materials and specifically in wavy composite layers has led to high margins of safety for the design of composite structures. Thus, the full lightweight potential of this class of materials is left unused. To understand the complex failure behavior of composite materials containing out...

The currently limited capability to predict material failure in composite materials in general and in wavy composite layers specifically has led to high margins of safety for the design of composite structures. Thus, the full lightweight potential of this class of materials is left unused. To understand the complex failure behaviour of composite ma...

o accurately simulate the foam core in composite parts on a macroscopic scale the morphology, the characterisation, and the nonlinear behaviour of thefoam must be understood properly. Accounting for the heterogeneity and the mechanical properties of the foam core affects the dimensioning of the final part.In the present study the microstructure of...

With an automated tape laying machine like the Fiberforge RELAY2000, spot-welded 2D layups of unidirectional fibre reinforced thermoplastic tape can be produced within short time. The layup process is usually followed by a consolidation step to remove the air of the layup and to fuse the plies. After this, the preforms can be formed into 3D parts....

The forming simulation of fibre reinforced thermoplastics could reduce the development time and improve the forming results. But to take advantage of the full potential of the simulations it has to be ensured that the predictions for material behaviour are correct. For that reason, a thorough validation of the material model has to be conducted aft...

Multi-zonal, electrically heated moulds for composite processing offer the potential of a direct heat introduction with low thermal lag and high energy efficiency. However, appropriate thermal dimensioning of these tools requires the consideration of the thermal response of the tool itself as well as the thermal and cure behaviour of the part, whic...

This study deals with the experimental investigation of the forming behaviour and the achievable component quality of thermosetting AFP-towpreg-laminates. For this purpose, components were processed with varying forming temperatures, clamping configurations, pre-heating temperatures, pressures and layups. The formed components were analysed regardi...

The aim of this study was to analyse the forming behaviour of glass fibre reinforced polypropylene and to identify the influence of several process parameters on the resulting part quality. For this purpose, a complex forming tool was designed, consisting of several areas with single and double curvature. The specimens were produced from unidirecti...

A complete simulation process chain has been used to predict the production and subsequent injection of over-braided textile preforms. A range of mandrel geometries and braiding configurations were used to illustrate how these factors affect the resin injection of the part. Braiding simulations were first completed, predicting the geometry of the b...

Damage and failure of triaxial braided composites under multi-axial stress states was investigated. In order to introduce different multi-axial stress states in the material, uni-axial tensile tests were performed at different off-axis orientations. Three braid architectures, comprising braiding angles of 30°, 45° and 60° were each loaded parallel...

The following work focuses on the experimental analysis of the forming behavior of fiber reinforced thermoplastic layups with a special focus on the radii. Possible factors influencing the result and quality of the forming shall be investigated. Considered parameters were the thickness of the layups, the fiber orientation, the size of the radius an...

Composite forming simulations consist in modelling the forming process of composite components to anticipate the occurrence of potential flaws such as out-of-plane wrinkles and fibre re-orientation. Forming methods often consist of automated processes in which flat composite blanks are forced to comply with tool geometries. Although Finite Element...

Automated fiber placement (AFP) process can be used to manufacture laminates by laying up unidirectional slit tapes along a desired path and placing multiple layers on top of each other. Usually, the slit tapes are placed direct onto the tooling to attain the final part geometry. Alternatively, the laminate can be built up on a planar substrate and...

This paper focuses on the mechanical characterization of biaxial braided composites under multiaxial stress states. Off-axis experiments in tension and compression were used to introduce multiaxial stresses in the material. The characterization was focused on nonlinear deformation and failure behavior: loading/unloading of the specimen was used to...

n the presented work, we propose a framework for predicting the non-linear mechanical response of triaxial braided composites using meso-scale finite element unit cells. Based on a reduced unit cell concept which exploits symmetries to minimise computational expense, a compacted and interpenetration-free yarn geometry is created within a three stag...

Out-of-autoclave prepreg processing requires evacuation of volatiles in the early stages of processing to achieve an acceptable final void content. In this study, single prepreg plies were laid-up onto a glass tool to simulate a ply–ply interface, to gain an understanding of initial air entrapment and eventual removal mechanisms. The contact was re...

Out-of-autoclave (OOA) prepregs are an attractive alternative to conventional autoclave materials in terms of costs, environmental impact and part size constraints. 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 proces...

The development of Finite Element (FE) thermoforming simulations of tailored thermoplastic blanks, i.e. blanks composed of unidirectional pre-impregnated tapes, requires the characterisation of the composite tape under the same environmental conditions as forming occurs. This paper presents a novel approach for the characterisation of transverse te...

Finite element analysis (FEA) of structural composites is mostly based on an as-designed geometry and input data. As-designed input data do not consider the manufacturing processes. For an as-built structural simulation of composites, it is important to integrate manufacturing process data into the structural analysis. Therefore, mapping algorithms...

Delaminations can change the mechanical behaviour of bonded joints significantly in crash simulations. A cohesive element is presented that enables the simulation of delamination failure in bonded joints on a full scale structural level. The principle of the approach is to compute the through thickness stresses of the adherends analytically within...

A three-dimensional nonlinear material model for fiber reinforced polymers is developed. The constitutive behavior is formulated based on mechanisms to allow for a minimum of material parameters. As a result, the model is able to capture complex nonlinear deformations under arbitrary loading conditions. Mechanisms like fiber reorientation induced b...

An improvement of a structural simulation for composite structures is realized with data sets from process simulations. A main challenge is to provide a mesh-independent interface for finite element (FE) data conversion. In this work, the FE data conversion for structural analysis is discussed. All relevant material parameter and model data can be...

A numerical study on the structural mechanics of bonded composite structures, which were interlaminary reinforced by metallic sheet and pin elements, is presented in this paper. For the investigation of the potential of this reinforcing technology, finite element models on meso and macro scale were studied, which were successfully validated against...

An approach to simulate the two-dimensional braiding process using a commercial explicit finite element software is presented. Preforms with generic shapes are analyzed. A procedure is given to determine the boundary conditions of the braiding mandrel including the extraction of necessary geometry information. The friction coefficients needed as in...

Ply waviness is a commonly observed manufacturing defect of ultra-thick composite materials essentially affecting stiffness, strength, and fatigue behavior of the composite. A specimen's geometry is designed to represent the failure mechanisms in thick wavy laminates, typically observed in spar caps of today's wind turbine blades. A material model...

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 r...

A continuum damage model for the prediction of the nonlinear response and the collapse of laminated composite structures is proposed. During laminate hardening the material model considers fiber rotation, plastic strain accumulation and inter-fiber damage to provide accurate ply stress information even at large deformations. In contrast to current...

A robust analysis of adhesively bonded joints requires valuable input data for simulation. Mechanical properties of adhesives in tensile and shear direction at high deformation rates are necessary, particularly for crash scenarios. Butt joint specimens and lap shear specimens were therefore tested under impact loading using a tensile split Hopkinso...

The influence of the stacking sequence on the nonlinear response of composite laminates is investigated. It is shown that a layup dependency solely emerges from damage evolution mechanisms, whereas damage initiation and viscoelastic and viscoplastic strain accumulation are not affected by the layup. This is a result of a proposed procedure that ena...

Most Out-of-Autoclave prepregs (OoA) are only partially impregnated with resin. Their impregnation completes during the cure cycle, solely driven by the difference between atmospheric and vacuum pressure. Increased part length leads to an impregnation time gradient caused by the transient air flow inside the fibrous medium. In this work, a novel nu...

The ability of a draping simulation to accurately predict the outcome of a forming process mainly depends on the accuracy of the input parameters. For pre-impregnated composites, material must be characterised in the same conditions as forming occurs, i.e. in temperature regulated environment. Given the issues encountered while testing specimens en...

Out-of-autoclave prepregs produce low-porosity parts through a complex consolidation process that includes air evacuation through a partially impregnated microstructure and subsequent resin infiltration flow. In this article, we propose, develop, and validate the first model describing this consolidation process by computing the thickness change of...

The quality of forming simulations based on Finite Element methods is mainly determined by the accuracy of the material properties. Out-of-plane bending is one of the deformation mechanisms that govern the appearance of wrinkles while forming composite reinforcements. This paper proposes a new test method using a Dynamic Mechanical Analysis (DMA) s...

A nonlinear constitutive model for composite laminates is developed with the focus on the distinction among inducing mechanisms. It is shown, that the effect of fiber rotation and damage is essential in consideration of large deformations. The evolution of yielding is described by two independent hardening curves either for in-plane shear or transv...

Material variations are always present even though Out-of-Autoclave prepregs are machine-made. They strongly determine the consolidation and may eventually lead to voids within the final part, depending on applied process conditions. To capture any contingencies, stochastic differential equations are derived to describe various interacting phenomen...

With the increasing demand for carbon fiber-reinforced parts in the aerospace industry, automated manufacturing methods such as automated fiber placement (AFP) are being established. To utilize AFP’s strong potential on multiple-curved surfaces such as chamfered sandwich structures, it is important to analyze and control emerging effects like gaps,...

One key aspect of the quality of parts attainable from the thermoset Automated Fibre Placement process is the impact of the heat source. For most industrial applications, an infrared heater is used and suitable process windows are still defined by trial-and-error approaches. Within this study, the need for robust thermal prediction tools is shown a...

Partially impregnated prepregs allow the vacuum to be distributed throughout the laminate and can transport air and volatiles outside the part. Air flow through the laminate and the latency of the matrix during the curing cycle strongly influence the resin-fibre wetting process. Non-optimized curing cycle can cause incomplete wetting of the initial...

Locally stitched non-crimp fabric preforms are stacked fabric layers that are sewn together. Using a seam improves the manufacturing process by providing tailored and easy to handle preforms. On the other hand, local stitching modifies the forming behaviour of the layup. Single-lap shear tests and modified bias-extension tests are used to character...

This paper presents the results of fracture mechanical tests on carbon reinforced composites. The evaluation of the experimental data leads directly to material properties for the further application in numerical crash simulations of automotive structures. If fibre bridging was detected within the composite’s failure surface, it could be quantitati...

A structural analysis for carbon composite is using a finite element analysis based on nominal definition of composite parts. Nominal material data sets can result unrealistic structural behavior. An improvement of simulation results can be realized with data sets from process simulations. Different finite element meshes augment a complexity of dat...

The characterisation of accurate material properties is a prerequisite for any forming simulation. Due to their characteristics, the mechanical behaviour of pre-impregnated Carbon Fibre Reinforced Polymers must be investigated under controlled environmental conditions, i.e. humidity and temperature. In this work, flexural properties in fibre direct...

Due to the partial impregnation and limited pressure available for curing Out-of-Autoclave (OoA) prepreg, modeling the air transport through the tows becomes applicable. Focus is given on predicting the tow fill time for through thickness resin flow taking into account the air evacuation state. This work presents models that can be applied at diffe...

In favor of an optimal utilization of the superior material properties of CFRP structures, the trend points towards more integral and thus geometrically more complicated structures. An understanding of the effect of various phenomena is difficult to develop for complicated geometries, thus investigation of main drivers on simply shaped subcomponent...

Out-of-autoclave (OOA) prepregs are an attractive alternative to conventional autoclave materials in terms of costs, environmental impact and part size constraints. For their successful and widespread application, the void content has to be restricted to that of benchmark autoclave structures. Thus, a detailed understanding of the consolidation pro...

In Elektrofahrzeugen von BMW kommen erstmals in großen Stückzahlen Strukturkomponenten aus CFK in Serienfahrzeugen zum Einsatz. Zu diesem Zweck wurde am Standort Landshut das Resin Transfer Molding (RTM)-Verfahren zur Fertigung von Automobilkomponenten industrialisiert. Der sequenzielle RTM-Herstellungsprozess führt dabei zu komplexen Wechselwirkun...

Out-of-autoclave (OOA) prepregs are an attractive alternative to conventional autoclave materials in terms of costs, sustainability and size constraints. However, due to low compaction pressure during cure, voids and porosity remain the main issue in OOA fabrication leading to reduced performance. To achieve the bench mark quality of autoclave stru...

Braided composites have a complex internal geometry with two or more sets of intertwined and undulated yarns. The internal geometry of a braided composite strongly depends on the shape of the desired component and on process parameters. This increases the demand for material characterization and constitutive modeling for structural analysis. This p...

Data transfer in the integrated toolchain for the simulation of composites

In the automotive industry, finite element simulation is widely used to ensure crashworthiness. Mechanical material data over wide strain rate and temperature ranges are required as a basis. This work proposes a method reducing the cost of mechanical material characterization by using the time-temperature superposition principle on elastomeric adhe...

Braiding is an automated preforming process for liquid molded composite materials. As braided composites offer a big variation in the textile yarn architecture, a material modeling approach has to predict the influence of yarn architecture on material stiffness and strength. The approach presented in this paper uses a finite element unit cell model...

Preforming of dry Non‐Crimp Fabric (NCF) enables a near‐net‐shape structure of CFRP‐parts before resin injection. Besides the common punch forming or hood forming, the diaphragm draping process offers greater possibility for automatable forming of textile reinforcements for composites. But the highly extendable membrane used to drape the preform ov...

In order to analyze viscoelastic behavior of particulatecomposites with growing damage, an existing three dimensionalviscoelastic continuum damage model developed originally for solidpropellant is generalized for wider use in a Finite Element model(FEM). This equation allows for damage induced anisotropy (localtransverse isotropy). The constitutive...

Reinforced plastics show a strong time-dependent behaviour which is due to the time-dependent behaviour of the matrix whereas their reinforcing fibres or particles are usually show time-independent behaviour. The aim of the present research project was to model this behaviour by the theory of visoelasticity and non-linear effects within the theory...

: Polymeric matrix composites show a strong time-dependent behaviour. This has also been observed in long-term tests conducted at our department. One of the most powerful tools to model this time dependent behaviour is the theory of viscoelasticity. Orthotropic isothermic linear behaviour is assumed for the material under study. A three-dimensional...