Use of a LHFB Device for Testing Mode III in a Composite Laminate.

Bertorello Bertorello,Bonhomme Bonhomme,Argüelles Argüelles,Viña Viña,Mollón Mollón

doi:10.3390/polym11081243

Abstract

The present paper studies the fatigue delamination behaviour of an epoxy/carbon composite material under mode III loading using a longitudinal half fixed beam (LHFB) device initially designed for mode III static tests of composite materials formed by the stacking of plies. For this purpose, a series of tests was carried out at different levels of loading representative of the fatigue behaviour of the material, from the crack onset phase through the delamination phase to final fracture. The experimental results were treated statistically, obtaining the values of the fatigue limit for probabilities of fracture of 5% and 50%. Finally, a fractographic analysis of the fracture surfaces was performed which allowed us to identify the same characteristic patterns of static mode III fracture, namely broken fibres, cusps and saw-teeth, in addition to a new morphology consisting of the formation of agglomerations of resin produced by the friction between the lips of the specimen in the fracture zone that point to dynamic mode III fracture. These agglomerations eventually crack and become detached from the fibres, leaving these free of resin.

Highlights

From the moment that the manufacture of plastic matrix composite materials from the successive stacking of plies was implemented at an industrial level, it was evident to all those involved that a series of materials with very good mechanical features had been obtained, but that these materials presented a weak point
As demonstrated in this paper, only the longitudinal half fixed beam analysing the mode III behaviour of materials of this type when they are subjected to dynamic (LHFB)
The high dispersion of the results shows that thisinbehaviour the material by tested occurs unsteadily, generally instantaneously when the initiation of a crack to fatigue the failure mode that occurs under this type of fracture stress in which the fatigue fracture occurs, of the i.e., without appreciable growth phase

Summary

Introduction

From the moment that the manufacture of plastic matrix composite materials from the successive stacking of plies was implemented at an industrial level, it was evident to all those involved that a series of materials with very good mechanical features had been obtained, but that these materials presented a weak point. A specific stress state is required ahead of the crack for it to effectively progress This is not necessarily a problem in any part that is in service and subject to load, provided that this possibility has been taken into account in its design. Many research groups subsequently adopted this specimen geometry mode III fracture is much more common compared to mode II fracture in this type of test specimen and the proposed loading mode [8,9,10,11]. The ECT device andof itsmaterials successiveofderivations have not been to be to valid for fatigue loading In this case, as demonstrated in this paper, only the longitudinal half fixed beam analysing the mode III behaviour of materials of this type when they are subjected to dynamic (LHFB). As demonstrated in this paper, only the longitudinal half fixed beam simple way.device [17,18] allows the fatigue behaviour of composite laminates to be studied in a relatively simple way

Experimental Procedure

E: Young’s modulus h: thickness

Presence of broken andin cusps in anear region

Conclusions