2,665 research outputs found
Interpretation of Size Effect in Orthogonal Machining of Composite Materials. Part I: Unidirectional Glass-Fibre-Reinforced Plastics
No full textOrthogonal cutting tests were carried out on unidirectional glass-fibre-reinforced plastics, using high-speed steel tools. During the tests, the tool rake and relief angle, and the depth of cut t were varied, whereas the cutting direction was held parallel to the fibre orientation. The trend of the principal forces recorded during cutting clearly showed the so-called `size effect': the unit cutting force (also known as `specific energy') was a decreasing function of the depth of cut, tending to infinity for vanishingly small values of t. A previous force scheme, assuming a significant influence of the friction generated by the work material sliding along the tool flank on the overall cutting forces, was utilized to interpret the cutting data, and to differently define the unit cutting force. According to the model, the unit cutting force and the coefficient of friction were independent of both the relief angle and the depth of cut, although the former, as expected, sensibly decreased with increasing the rake angle
Electromagnetic heating for adhesive melting in CFRTP joining: study, analysis, and testing
No full textInduction heating of thermoplastic composites is a suitable and promising technique, due to the very short heating time and the possibility of generating the heat at the interface between the adherends compared with other heating technologies, i.e. owen heating or hot melt gun manual deposition. The aim of this work is to study the electromagnetic induction heating in adhesive bonding of thermoplastic matrix composite materials, when a hot-melt thermoplastic adhesive, Prodas, is used. A numerical model for studying the effect of the process parameters, such as current intensity, maximum temperature and holding time at maximum temperature, has been developed. Experimental tests validated the results of the numerical model; also, the mechanical properties of the adhesive joints were evaluated by short beam shear test and single lap shear tests to define the values of technological parameters allowing for the better joint strength. Moreover, ANOVA analysis was employed to evaluate the most significant parameter which affected the mechanical properties, highlighting the optimum process parameters
l-Elisionen bei sollen und wollen im Rautendorfer Platt
No full textOnline-Anhang zum Artikel: Wiegmann, Nele. 2025. l-Elisionen bei den Verben sollen und wollen. Das Rautendorfer Platt im Vergleich mit anderen niederdeutschen und weiteren westgermanischen Varietäten. In: Schuhmann, Katharina S. & Rohloff, Tio & Stolz, Thomas (Hg.), Linguistik im Nordwesten. Beiträge zum 15. Nordwestdeutschen Linguistischen Kolloquium (NWLK) 2023 in Oldenburg (Studien zur Sprachwissenschaft 7), 97–127. Baden-Baden: Georg Olms Verlag
Technological characterisation of thermoshrinking cross-linked polyethylene by destructive and non-destructive techniques
No full textThe attention of the present work is focused on the characterisation of thermoshrinking cross-linked polyethylene, which is produced at the Megarad s.r.l. firm and which is mostly used as insulation for electrical cables of low and medium voltage, protection for communication cables, anti-corrosion protection for gas pipes. Two cross-linking processes: chemical (silane grafting) and electron beam irradiation are employed. The performance of the end product is verified by means of both destructive and non-destructive tests. Some parameters such as: gel fraction, modulus of elasticity at 150 °C and elongation percent are measured. Non-destructive tests are carried out by means of lock-in thermography; the variation of the phase angle with increasing the cross-linking degree is related to the variation of the modulus of elasticity. It is found that the thermographie technique is capable of giving information about material modifications arising under cross-linking and is also able to detect defects which may form during manufacturing. © 2002 Elsevier Science B.V. All rights reserved
Healcon: self-healing concrete to create durable and sustainable concrete structures
No full textWithin the theme ‘Self-healing materials for prolonged lifetime’ (NMP.2012.2.1-3) of the Seventh Framework Programme, self-healing concrete is an important topic. The project HEALCON, which deals with self-healing concrete to create durable and sustainable concrete structures, is funded by EU-FP7 and started in January 2013. The coordinator of the project is Prof. Nele De Belie (UGent) and the consortium partners are UGent, Avecom, TU Delft, Acciona, TUM, TTI, VTT, COWI, DTI, CEINNMAT, Devan and Fescon.
Adequate perpetuation of the road, tunnel and bridge network, is crucial to preserving European cohesion and business operations; and around 70% of this infrastructure is made of concrete. In order to garantuee liquid tightness of concrete structures, and enhance durability of elements prone to bending cracks, smart concrete with selfhealing properties will be designed.
Thanks to the existing expertise of the consortium in the field of self-healing concrete at a lab-scale, a thoughtful selection of promising techniques is possible.
- For early age cracks, a non-elastic repair material can be proposed, such as calcium carbonate precipitated by bacteria, or new cement hydrates of which the formation is stimulated by the presence of hydrogels.
- For moving cracks under dynamic load, an elastic polymeric healing agent is suggested.
Different healing agents and encapsulation techniques are tested and scaled up. Self-healing efficiency is evaluated in lab-scale tests using purposefully adapted monitoring techniques, and optimized with the help of suitable computer models.
Finally the efficiency is validated in a large scale lab test and implemented in an actual concrete structure. Life-cycle cost analysis will show the impact of the selfhealing technologies on economy, society and environment compared to traditional construction methods
On the origin of cutting forces in machining unidirectional composite materials
No full textShort-term and wear cutting tests were carried out on unidirectional graphite fibre reinforced composites, holding the cutting direction coincident with fibre orientation. During the tests, performed with high speed steel tools, the tool rake and relief angle, and the depth of cut were varied. The observation of tool worn surfaces after wear tests revealed absence of friction along the face; on the contrary, an intense sliding of the work against the tool flank was suggested by the flank surface morphology. Consequently, a force scheme consistent with the information gathered from tool wear examination was built. It is shown that, when the experimental cutting forces are treated according to the new force scheme, the coefficient of friction, f, can be considered independent of the tool geometry and the depth of cut, t. Besides, the unit cutting force X is unaffected by the depth of cut, although it is a decreasing function of the rake angle. On the contrary, if the simplified hypotheses generally adopted in metal cutting are used, both f and X strongly vary with the depth of cut. In particular, the unit cutting force notably increase with decreasing t, undergoing the well known `size effect'
Technological characterization of thermoshrinking cross-linked polyethylene by destructive and non-destructive techniques
No full textThe attention of the present work is focused on the characterisation of thermoshrinking cross-linked polyethylene, which is produced at the Megarad s.r.l. ®rm and which is mostly used as insulation for electrical cables of low and medium voltage, protection for communication
cables, anti-corrosion protection for gas pipes. Two cross-linking processes: chemical (silane grafting) and electron beam irradiation are employed. The performance of the end product is veri®ed by means of both destructive and non-destructive tests. Some parameters such as:
gel fraction, modulus of elasticity at 1508C and elongation percent are measured. Non-destructive tests are carried out by means of lock-in thermography; the variation of the phase angle with increasing the cross-linking degree is related to the variation of the modulus of elasticity. It
is found that the thermographic technique is capable of giving information about material modifications arising under cross-linking and is also able to detect defects which may form during manufacturing
Optimization of DDE-phytoremediation by exploiting plant-associated bacteria and nanoparticles
No full textIntroduction Researchers at The Connecticut Agricultural Experiment Station observed a
remarkable difference in DDE accumulation at the subspecies level of Cucurbita pepo. C.
pepo ssp pepo accumulates DDE, while C. pepo ssp ovifera did not possess this capacity. In a
first part, this study investigates whether the the differences in DDE accumulation can be
related to differences in the plant-associated bacterial populations of the different subspecies .
Bacteria were isolated from both seeds and plants of accumulating and non-accumulating
Cucurbita pepo subspecies. The plants were exposed to 100 μg L-1 DDE.
The second part of this projects concentrates on silver nanoparticles (AgNPs) and their
capability to increase the uptake of organic contaminants by plants. Here, the possibility to
optimize DDE phytoremediation by exploiting both plant-associated bacteria as well as
AgNPs was investigated. Plants were exposed to 100 μg L-1 DDE, 500 mg L-1 AgNPs or both.
The effects of DDE and AgNPs on plant growth and on the associated bacterial populations
were investigated. Plant biomasses were determined and endophytes from both subspecies in
all conditions were isolated. All isolated bacteria were subjected to (1) genotypic
identification, (2) characterization of their plant growth promoting capacity, (3) screening for
AgNP toxicity and (4) screening for DDE degradation capacity.
Results DDE proved to have a toxic effect on plant growth, while AgNPs did not cause a
decrease in biomass. The effect on the total number of plant-associated bacteria that could be
isolated was the opposite. While DDE increased the number of endophytes in zucchini Raven,
exposure to AgNPs caused a severe decrease. Endophytes associated with zucchini Raven
demonstrated more plant growth promoting capacities than squash-associated bacteria.
Bacteria that were isolated from plants that were exposed to DDE or AgNPs showed to
experience less toxic effects when again exposed to these products.
Conclusion The DDE accumulator Zucchini Raven contains a higher number and diversity of
associated bacteria and its bacteria show more plant growth promoting capacity and potential
DDE degradation capacity than the bacteria associated with the non-DDE-accumulator squash
Zephyr. These findings and the higher DDE-uptake of zucchini Raven makes it a suitable
organism for DDE phytoremediation.
On one hand, AgNPs can be used to increase the DDE uptake of Cucurbita pepo, but on the
other hand it has severe toxic effects on the plant-associated bacteria. Therefore, a good
balance has to be discovered between the advantages and disadvantages of AgNPs for
bacteria-enhanced phytoremediation of DDE using Cucurbita pepo ssp. pepo
Effect of tool wear on cutting forces in the orthogonal cutting of unidirectional glass fiber reinforced plastics
No full textOrthogonal cutting tests were carried out on unidirectional glass fibre-reinforced plastic composites, holding the cutting direction parallel to the fibre direction. The tools were made of high speed steel, with rake angle alpha = 0 degrees; two relief angles gamma, namely 7 degrees and 15 degrees, were adopted. A very low cutting speed was utilized, in order to avoid thermal effects on both the tool and the work material. The experimental results show that, under the selected operating conditions, the tool wear essentially consists of a very rapid rounding of the tool nose (nose wear). The face wear evolution is practically independent of the relief angle, whereas the latter affects the flank wear rate, which is slightly lower for the higher gamma value. Both the horizontal and the vertical cutting forces exhibit notable increases with tool wear. The force data are interpreted in the light of a previously presented model, aiming to predict cutting forces as a function of the cutting parameters. It is shown that the observed increase in the horizontal force can be simply attributed to the increase in the vertical force at the tool flank, whereas the chip-tool interaction forces occurring at the tool face seem to be unaffected by wear phenomena. Finally, a strict correlation is found between the flank wear and the recorded vertical force variations
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