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1

Parametric characterization of a mesomechanic kinematic in plain and twill weave 2/2 reinforced composites by FE-calculations

Romano M., Ehrlich I., Gebbeken N.

Archives of Materials Science and Engineering

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2019

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Vol. 97, nr 1/2

20--38

EN

Purpose: A parametric characterization of a mesomechanic kinematic caused by ondulation in fabric reinforced composites is investigated by numerical investigations. Design/methodology/approach: Due to the definition of plain representative sequences of balanced plain-weave and twill-weave 2/2 fabric reinforced single layers based on sines the variable geometric parameters are the amplitude and the length of the ondulation. Findings: The mesomechanic kinematic can be observed in the FE analyses for both kinds of fabric constructions. Research limitations/implications: The FE analyses consider elasticity and contraction due to Poisson effects, respectively, of the model under selected longitudinal strains. Practical implications: The results are evaluated at relevant positions on the centre-line of the ondulated warp-yarn of the plain representative model. A direct and linear coupling in case of the transversal kinematic behaviour, and thereby a corresponding definite reduction of the evaluated longitudinal strains in terms of the difference of the applied and determined longitudinal strains is identified. Originality/value: Both characteristic purely kinematic reactions due to geometric constraints directly depend on the introduced degree of ondulation. This non-dimensional parameter relates amplitude and length of one complete ondulation, and thus represents the intensity of the ondulation of the respective fabric construction.

2

Structural mechanic material damping in fabric reinforced composites: a review

Romano M., Ehrlich I., Gebbeken N.

Archives of Materials Science and Engineering

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2017

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Vol. 88, nr 1

12--41

EN

Purpose: A review regarding the acting mechanisms of structural dynamic material damping in fabric reinforced composites is presented. Design/methodology/approach: Mechanical acting principles identified by different investigations are considered. Aspects of the determination and calculation of structural mechanical material properties of fabric reinforced composites are described. Approaches intending the description and classification of ondulations in fabrics reinforced single layers are demonstrated. Findings: The mesomechanic geometry of fabrics is not considered sufficiently by relatively simple homogenization approaches. Yet, it significantly affects its structural dynamic material properties, especially the dynamic ones. Research limitations/implications: In each case the different damping mechanisms act coupled and occur at the same time. Therefore a separation procedure is required in any case. Practical implications: Against the background of the comparison and remarks of the presented papers a reasonable further procedure is recommended. Thereby, FE-calculations with a parametrical variation of the mesomechanic geometry in order to identify kinematic correlations due to geometric constraints are suggested. Originality/value: The idea of the representation of the geometric conditions in terms of a degree of ondulation is described. Such a non-dimensional specific value representing the intensity of the ondulation would enable the comparability of the results of different kinds of investigations.

3

Influence of parameters of the production process on the material quality of unidirectionally reinforced prepregs

Romano M., Eisenried M., Jungbauer B., Ehrlich I., Gebbeken N.

Journal of Achievements in Materials and Manufacturing Engineering

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2015

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Vol. 68, nr 1

32--44

EN

Purpose: A prepreg production device in laboratory scale is used to develop the production process of unidirectionally reinforced prepregs. Design/methodology/approach: The aim of the prepreg production device is to impregnate different types of reinforcement fibers with an arbitrarily selectable thermoset matrix system that completely satisfies the requirements for autoclave processing. As the prepreg production device is designed and built up modularly every module corresponds one step in the process. Findings: To identify the parameters of the production process and investigate its sensitivity on the material quality of both the prepreg as an uncured semi-finished product and the composite as the cured material experimental investigations regarding the resin flow, fiber volume content, mass per unit area and void content are carried out. Overall four material combinations have been investigated, where in each case the selected impregnation temperature and the width of the impregnation gap has been reproducibly varied in selected steps. Research limitations/implications: The experimental characterization of the prepregs and of the composite material is carried out according to German standards. Originality/value: Used parameters clearly affect the material properties, so that a proper impregnation and curing process can be achieved by optimizing the parameter to desired values.

4

Comparison of impact delaminations in CFRP using different test methods

Ehrlich I., Dinnebier H., Jost C.

Journal of Achievements in Materials and Manufacturing Engineering

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2015

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Vol. 73, nr 2

128--138

EN

Purpose: of this paper is comparison of impact delaminations in CFRP using different test methods. Design/methodology/approach: A comparison is made between the results of well-established techniques such as Ultrasonic Testing or micrographic cross-sections with the results of Microfocus Computed X-Ray Tomography. Findings: The findings show that both Ultrasonic Testing and μCT show a linear correlation between impact energy and delaminated area. However, μCT is able to detect significantly larger delaminated areas. Other findings were that the undamaged zone immediately underneath the contact point of the impactor is not a cylinder but a cone segment. The higher density of that compacted area could also be visualized. Research limitations/implications: The correlation between main impact parameters could be shown on the base of state of the art non-destructive testing. Originality/value: Impact delaminations in carbon fiber reinforced plastic have generated in a well-defined manner and a comparison is made between the results of well-established techniques such as Ultrasonic Testing (UT) or micrographic cross-sections with the results of Microfocus Computed X-Ray tomography (μCT).

5

The effects of severe temperature changes and high humidity on porous CFRP

Dinnebier H., Ehrlich I.

Journal of Achievements in Materials and Manufacturing Engineering

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2014

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Vol. 67, nr 1

14--20

EN

Purpose: A route to manufacture porous carbon fiber reinforced plastic (CFRP) for study purposes is described. Design/methodology/approach: The porous CFRP is characterized using standard techniques such as matrix digestion as well as the more sophisticated method of high resolution Microfocus X-Ray Tomography (μCT). A comparison of the results of those methods is presented. The mass gains of specimens with a wide range of porosity have been measured both in constant humidity and in alternating environments. Findings: It could be shown that severe temperature changes can temporarily increase the moisture content of porous CFRP. However, after the return to a constant environment, the moisture content returns back to saturation levels. Furthermore, it could be shown by X-Ray Tomography that even under severe climatic conditions no permanent liquid water condensates inside the pores. Research limitations/implications: Using Microfocus Computed Tomography it could be shown that even after nearly a year under hot-wet conditions and more than 150 severe temperature cycles there is no liquid water detectable inside the pores. Originality/value: In this paper the effects of severe temperature changes and high humidity on porous CFRP.

6

Experimental investigation of energy dissipation properties of fibre reinforced plastics with hybrid layups under high-velocity impact loads

Romano M., Hoinkes C., Ehrlich I., Höcherl J., Gebbeken N.

Journal of Achievements in Materials and Manufacturing Engineering

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2014

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Vol. 64, nr 1

5--19

EN

Purpose: The present work deals with the experimental investigation concerning the energy dissipation capacity of different kinds of reinforcement fibres in monolithic and hybrid layups under high velocity impact loads. The investigated kinds of fibres are carbon, glass and basalt. Design/methodology/approach: The test panels have been impregnated with thermoset resin. Curing was done by autoclave processing. In order to obtain comparable fibre volume contents of approx. 60 % in the different layups (monolithic and hybrid without and with separating layer), curing cycles adapted to the type of layup have been identified. The resulting fibre volume content of the test panels has been determined both by weighing and experimentally by chemical extraction and calcination. The impact load was applied by an instrumented experimental setup. Thereby both commercially available bullets and bearing balls accelerated with weighted propellant in a sabot have been used as impactors. The measured values are the velocities of the bearing balls as the impactor before and after penetration of the test panels. Findings: In both cases the results show the energy dissipation capacity of each single kind of fibre in case of the monolithic layups as well as the enhanced properties of the hybrid stacked layups without and with the separating layer as a core material. Typical failure modes on the impact surface and on the outlet areas are identified. Research limitations/implications: The influence of the respective kind of impactors, namely bullets and bearing balls, on the evaluated results is identified. Thereby the bearing balls exhibited a higher degree of reproducibility due to several reasons. Originality/value: Fibre reinforced plastics with hybrid stacking sequences can be used as load-bearing structures and at the same time as safety structures for passengers in automotive or aerospace applications. Moreover, with the hybrid stacked composites lightweight concepts can efficiently be realized regarding energy saving issues.

7

Experimental investigation of damping properties of unidirectionally and fabric reinforced plastics by the free decay method

Romano M., Micklitz M., Olbrich F., Bierl R., Ehrlich I., Gebbeken N.

Journal of Achievements in Materials and Manufacturing Engineering

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2014

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Vol. 63, nr 2

65--80

EN

Purpose: of this paper is experimental investigation of damping properties of unidirectionally and fabric reinforced plastics by the free decay method. Design/methodology/approach: For the evaluation of the presumed effect experimental structural dynamic investigations comparing unidirectionally and fabric reinforced plastics are carried out. In detail the free decay behaviour of flat beamlike specimens under fixed-free boundary conditions and relatively constant and reproducible displacement excitation is investigated. Findings: The vibrating structure has been measured by a laser scanning vibrometer PSV 400 from POLYTEC. In both cases evaluation of the results yields enhanced damping properties of the specimens with fabric reinforcement compared to the unidirectionally reinforced specimens. The results justify the presumed acting of a mesomechanic kinematic. Research limitations/implications: The results show that in either case the material damping in terms of the logarithmic decrement of the fabric reinforced material is higher than the material damping in of the unidirectionally reinforced material. Additionally, when the fabric reinforced specimens are addressed, in each case the plain weave reinforced specimens exhibited higher values of the material damping as the twill weave 2/2 reinforced ones. Originality/value: Ondulations in fabrics as a textile semi-finished product are caused by the alternating crossing of warp and fill yarns. In the mesoscopic scale the acting of a mesomechanic kinematic is presumed to enhance the damping properties under cyclic elastic deformation. For the evaluation of the presumed effect experimental structural dynamic investigations comparing unidirectionally and fabric reinforced plastics are carried out.