Project

Mechanical Disintegration of Hardwood (HARDIS)

Goal: The goal of the project, funded by Interreg ATCZ, is to generate a comprehensive understanding of mechanisms taking place during the disintegration of wood. Therefore methods are developed enabling the examination of the cutting process at different cutting directions at currently used cutting speeds. By means of cutting force and deformation measurements as well as analysis of failure mechanisms a FEM Model will be developed. The project (07/2017 – 06/2020) is a cooperation of the Department of Wood Science, Faculty of Forestry and Wood Technology, Mendel University (Brno) and Wood K plus, Area Wood Materials and Technologies (Kompetenzzentrum Holz GmbH, Tulln).

Methods: High Speed Imaging, FEM Simulation, DIC, cutting force mesurement (piezo sensor), Digital Image Correlation

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Project log

Jan Tippner
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The link to the video about the Interreg ATCZ HARDIS project: https://youtu.be/dJbuVqrlZ9Y
 
Jan Tippner
added 2 research items
The hardwood, as a natural composite, may be subjected to the dynamic loading in many applications, such as the high-speed disintegration or structural collapses. The correct material description is needed for finite element modelling that can take place in the design stages of wood manufacturing processes or building the wooden structures. The split Hopkinson pressure (Kolsky) bar test provides the data for high strain rates. The experiments were carried out on the European beech wood in all the principal loading directions. The tests were repeated computationally in order to obtain the material constants of the complex material model, which covered the anisotropy of elasticity, plasticity as well as fracture behaviour. Moreover, the failure was considered non-symmetric with respect to the tension and compression. This was achieved by incorporating the stress triaxiality dependency into the failure model. The crack initiation and propagation were realized through element deletion technique within LS-DYNA code. The real behaviour was captured quite well including the pulses in the incident and transmission bars.
Previous methods for the investigation of high-speed cutting processes for bio-based materials failed since essential principles for the investigation of dynamic processes have not been taken into account. The novel self-developed device, based on the principle of a rotor arm, enables a detailed analysis of cutting processes. The rotor arm has a diameter of 4 m, enabling precise analysis of cutting processes. The device enables analysis of speeds up to 100 m/s of the more or less linear cutting process. Stiffness of the set-up, the natural frequency of the system, and a series of cuts per test may cause a convoluted signal demanding dynamic calibration of the measurement chain. The newly developed device enables the conduction of single cuts per examination at relatively high speed. Thus, the influence of the previous cut is eliminated. Previous research has not provided a possibility to study linear cutting processes at the mentioned velocity. The accuracy of the device was proven within various examinations. A correction based on real chip thickness measurement was applied. Finally cutting of beech, using a wide set of parameters, was examined. The cutting forces of the beech sample increased linearly with chip thickness. Nevertheless, the influence of velocity showed non-linear progression. The smallest force was observed at 20 m/s. From this cutting speed, force always increased when velocity was changed.
Stephan Frybort
added an update
Invitation to on-line workshop
Our project is aimed at the investigation of cutting forces during the hardwood disintegration. We developed new technology capable of producing the cutting speed of approximately 100 m/s. During our workshop, we would like to share with you our results and discuss new ideas and contributions to this topic.
Link to join workshop:
Film about the project:
 
Stephan Frybort
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Determination of dynamic material propoerties for Finite Element Modelling
 
Stephan Frybort
added an update
Consideration of the dynamic properties is the basic prerequisite for successful dynamic measurements. Based on extensive planning and careful construction of the test set-up, we achieved a measuring chain showing perfect dynamic properties. Natural frequency of the measuring chain (force sensor, knife holder etc.) amounts to 3 kHz. This makes it possible to measure cutting processes up to 100 m/s, without investing much effort in data correction. However, further improvement measures are planned (e.g. weight reduction etc.).
 
Stephan Frybort
added an update
Programming of the controlling software was successfully finished. Machine table movement, i.e. adjustment of chip thickness, is achieved within the desired time span of half a rotation of the rotor arm.
Rotation speed was gradually increased leading to a cutting speed of ~90 m/s. Target speed is 100 m/s which corresponds to 8 Hz.
First measurements were carried out successfully (cutting force measurement and high speed camera recordings).
 
Stephan Frybort
added an update
First tests showed realy smooth running of the rotorarm at around 25 m/s. As a next step the safety housing could be closed and exactly aligned.
The hardware and the software of the machine table was updated, so the necessary reaction time and speed of movement can be achieved now (see figure).
Next steps are wiring and programming
 
Stephan Frybort
added an update
decision about applied sensors for controlling and measuring is finished
ordering process (Interreg!) completed
 
Stephan Frybort
added an update
Colleagues from Wood K plus and Mendel University checked out the new measurement equipment, which was therefore implemented into the test set-up for low dynamic cutting examinations
 
Adam Ekielski
added an update
The updated Hardis website is available by clicking on the link: https://hardis.org/en/
 
Adam Ekielski
added an update
Photogrammetrically techniques (Digital Image Correlation) become an important and no contacting measurement method used to measure and evaluate deformations during dynamic loads.
The DIC method consists in recording and analysing displacement and deformation fields on the surface of the tested object using correlation of digital images of the tested object recorded during its displacement or deformation.
DIC displacement and deformation can be measured using a system of one, two or more cameras. The use of one camera allows to determine the displacements and deformations of the tested sample only in the plane parallel to the image plane of the camera matrix. Using at least two cameras to record the image of a test object in different directions, it is possible to measure displacements and deformations in three-dimensional space.
The algorithm used for image analysis consists of three basic steps:
1. The system's digital camera analysing the sample area searches for characteristic points that become reference points for the virtual grid and for discretization of the analysed area.
2. On the basis of the recorded changes in the distance between the points and numerical evaluation, a displacement and deformation map is created for the entire surface of the material seen by the camera.
3. Two estimation models are used for the DIC method:
· Normalised Cross Correlation (NCC)
· Least-Squares Matching (LSM).
 
Stephan Frybort
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Funded by Interreg ATCZ
 
Stephan Frybort
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Stephan Frybort
added an update
The basis design of the measurement test setup is completed. FEM analysis of the rapidly rotating and therefore highly stressed components showed satisfying results.
Next steps are acquisition of necessary measuring components, e.g. force sensor, and the development of the measurement chain.
 
Stephan Frybort
added a project goal
The goal of the project, funded by Interreg ATCZ, is to generate a comprehensive understanding of mechanisms taking place during the disintegration of wood. Therefore methods are developed enabling the examination of the cutting process at different cutting directions at currently used cutting speeds. By means of cutting force and deformation measurements as well as analysis of failure mechanisms a FEM Model will be developed. The project (07/2017 – 06/2020) is a cooperation of the Department of Wood Science, Faculty of Forestry and Wood Technology, Mendel University (Brno) and Wood K plus, Area Wood Materials and Technologies (Kompetenzzentrum Holz GmbH, Tulln).