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Hysteresismessungen zur Charakterisierung der mechanisch-dynamischen Eigenschaften von R-SMC

In this thesis, the influence of the major composition components of R-SMC: glasfibre, mineral filler and resins with differing shrinkage compensation on the mechanical property profile of R-SMC under static-, impact and dynamic fatigue loading was investigated. To evaluate the dynamic fatigue properties of R-SMC, the Hysteresis Measurement Method was applied. Microscopical investigations enable to establish structure property relationships.

By systematic modifications of the material composition it was possible to prove, that the particles of the mineral filler are the materials weak point beeing responsible for a low damage limit. Stress concentrations localised at the vertex of the particles and localised strain overloads in the resin between adjacent filler particles are leading already at low tensile loadings to multiple cracking caused by delamination in the interphase between resin and filler. Beside the abolute content of fillers by volume the particle size distribution curve and the related specific surface area and packing density of the filler particles have an improtant influence on the level of the critical damage limit.

Under static and dynamic loading, with the starting limit of multiple cracking an upper application limit is defined, because the crack development is finally responsible for a significant lost in stiffness of the material. This is accompanied with the risk, that penetrating chemicals are able to attack the SMC-material. The heterogenious microstructur of R-SMC is in addition responsible for a high overall scatter of all mechanical properties.

It is shown in this thesis, that numbers of cycles to failure and the residual strength are less suitable to qualify the dynamic fatigue properties of R-SMC because for the fracture point the network structure of the glasfibers is responsible, but for the in praxis relevant damage limit, the initiation of multible cracking is responsible.

Because SMC-materials exhibit a high lost in stiffness under fatigue loading, not the number of cycles to failure should be used for the engineering assessment of the fatigue behaviour but the relative change in stiffness of the material is relevant as determined by Hysteresis Measurements.

Lesen Sie die deutsche Zusammenfassung auf Kunststoffe.de
Author
 Volker Altstädt

Volker Altstädt
Institut für Werkstofftechnik
Universität - Gesamthochschule Kassel

Information

Free keywords: R-SMC, composition, filler, multiple cracking, dynamic fatigue properties, Hysteresis Measurements, structure property relationship
Institute / chair: Institut für Werkstofftechnik der Universität - Gesamthochschule Kassel
Language: German
Technical consultant for expert services: Prof. Dr.-Ing. Dr. h.c. Gottfried W. Ehrenstein (Betreuer), Prof. Dr.-Ing. Helmut Wohlfahrt, Prof. Dr.-Ing. Helmut Schaper
Publication year: 1987
Provider: Wissenschaftlicher Arbeitskreis Kunststofftechnik (WAK) / Kunststoffe.de

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