Damage Mechanisms in Loaded Aramid Composites by Means of Embedded PVDF Acoustic Emission Sensors

2006 ◽  
Vol 13-14 ◽  
pp. 337-342 ◽  
Author(s):  
Claudio Caneva ◽  
I.M. De Rosa ◽  
F. Sarasini
Keyword(s):  
Acoustic Emission ◽  
Composite Materials ◽  
Polyvinylidene Fluoride ◽  
Structural Integrity ◽  
Fibrous Composite ◽  
Failure Mechanisms ◽  
In Situ Monitoring ◽  
Epoxy Composites ◽  
Pvdf Film ◽  
Emission Data

Cost-effective and reliable damage detection is critical for the utilization of composite materials due to the relatively localised nature of damage formation and the resultant reduction in structural integrity. Of the methods available, Acoustic Emission (AE) is considered as one potential technology for on-line and in situ monitoring of structural degradation of composite materials. Purpose of this work was to study the interaction between embedded PVDF (polyvinylidene fluoride) transducers and composite samples as well as detect and characterize the failure mechanisms in aramid/epoxy flexural test specimens using acoustic emission data obtained by embedded PVDF film sensors. Furthermore, it has been realized a comparison with surface mounted PVDF data. Results of our previous works (Caneva et al., 2005) dealing with monitoring tensile and flexural behaviour of glass/epoxy composites enabled to extend this methodology to aramid/epoxy composites. The use of Acoustic Emission and Scanning Electron Microscopy (SEM) observations enabled to identify and understand the failure mechanisms of the composites tested. Furthermore, satisfactory results of this work highlighted that the application of PVDF shows promise as a suitable acoustic emission transducer for fibrous composite materials.

scholarly journals Physical modelling of failure in composites

2016 ◽  
Vol 374 (2071) ◽  
pp. 20150280 ◽  
Author(s):  
Ramesh Talreja
Keyword(s):  
Composite Materials ◽  
Failure Modes ◽  
Structural Integrity ◽  
Failure Mechanisms ◽  
Local Stress ◽  
Physical Modelling ◽  
Stress Fields ◽  
Systematic Analysis ◽  
Composite Failure ◽  
Failure Theories

Structural integrity of composite materials is governed by failure mechanisms that initiate at the scale of the microstructure. The local stress fields evolve with the progression of the failure mechanisms. Within the full span from initiation to criticality of the failure mechanisms, the governing length scales in a fibre-reinforced composite change from the fibre size to the characteristic fibre-architecture sizes, and eventually to a structural size, depending on the composite configuration and structural geometry as well as the imposed loading environment. Thus, a physical modelling of failure in composites must necessarily be of multi-scale nature, although not always with the same hierarchy for each failure mode. With this background, the paper examines the currently available main composite failure theories to assess their ability to capture the essential features of failure. A case is made for an alternative in the form of physical modelling and its skeleton is constructed based on physical observations and systematic analysis of the basic failure modes and associated stress fields and energy balances. This article is part of the themed issue ‘Multiscale modelling of the structural integrity of composite materials’.

Aspects of Strain Rate Effects on Some Composite Materials

2000 ◽  
Author(s):  
Emmanuel O. Ayorinde
Keyword(s):  
Acoustic Emission ◽  
Composite Materials ◽  
Strain Rate ◽  
Matrix Cracking ◽  
Epoxy Composites ◽  
Fiber Architecture ◽  
Strain Rate Effects ◽  
Rate Effects ◽  
General Strain ◽  
Ultrasonic Images

Abstract Effects of moderate straining speed on the material and damage characteristics of beam samples of graphite/epoxy and E-glass/epoxy composites were investigated. The basic fiber architecture utilized was unidirectional, axial layup, but data was also obtained for the 45-degree orientation. Ultrasonic and acoustic emission (AE) inspections were utilized. The acoustic emission records show matrix cracking. The ultrasonic images revealed the regions of failure. The results show that in general, strain rate notably affects material and damage properties.

scholarly journals Modelling the development of defects during composite reinforcements and prepreg forming

2016 ◽  
Vol 374 (2071) ◽  
pp. 20150269 ◽  
Author(s):  
P. Boisse ◽  
N. Hamila ◽  
A. Madeo
Keyword(s):  
Composite Materials ◽  
Structural Integrity ◽  
Fibrous Composite ◽  
Bending Stiffness ◽  
Textile Composite ◽  
Forming Process ◽  
Transition Zones ◽  
Process Simulations ◽  
Composite Reinforcement ◽  
Composite Reinforcements

Defects in composite materials are created during manufacture to a large extent. To avoid them as much as possible, it is important that process simulations model the onset and the development of these defects. It is then possible to determine the manufacturing conditions that lead to the absence or to the controlled presence of such defects. Three types of defects that may appear during textile composite reinforcement or prepreg forming are analysed and modelled in this paper. Wrinkling is one of the most common flaws that occur during textile composite reinforcement forming processes. The influence of the different rigidities of the textile reinforcement is studied. The concept of ‘locking angle’ is questioned. A second type of unusual behaviour of fibrous composite reinforcements that can be seen as a flaw during their forming process is the onset of peculiar ‘transition zones’ that are directly related to the bending stiffness of the fibres. The ‘transition zones’ are due to the bending stiffness of fibres. The standard continuum mechanics of Cauchy is not sufficient to model these defects. A second gradient approach is presented that allows one to account for such unusual behaviours and to master their onset and development during forming process simulations. Finally, the large slippages that may occur during a preform forming are discussed and simulated with meso finite-element models used for macroscopic forming. This article is part of the themed issue ‘Multiscale modelling of the structural integrity of composite materials’.

scholarly journals Fluctuations of 1/f Noise in Damaging Structures Analyzed by Acoustic Emission

2018 ◽  
Vol 8 (9) ◽  
pp. 1685 ◽  
Author(s):  
Alberto Carpinteri ◽  
Giuseppe Lacidogna ◽  
Federico Accornero
Keyword(s):  
Acoustic Emission ◽  
Power Spectra ◽  
In Situ Monitoring ◽  
Critical Conditions ◽  
Noise Power ◽  
Structural Elements ◽  
Emission Data ◽  
Frequency Fluctuations ◽  
Physical Quantities

It is well known in literature that frequency fluctuations of different physical quantities clearly show 1/f noise power spectra. In the present work, the authors observe that in some brittle materials, such as concrete, masonry, and mortar, Acoustic Emission (AE) signals, generating from brittle fracture phenomena, exhibit a frequency fluctuation approaching to 1/f. Acoustic Emission data obtained from laboratory tests on concrete samples, and from in-situ monitoring of some important Italian historical buildings are reported in terms of spectral density vs. frequency. It is shown that in structural elements subjected to different load conditions, the frequency fluctuations are 1/f like. The study and interpretation of these phenomena through the use of the AE technique can be therefore very useful for identifying the transition from the critical conditions of a structure to those that involve an incipient collapse.

Acoustic Emission Monitoring of Composite Plates Under Buckling Loads

2012 ◽  
Author(s):  
S. Abazary ◽  
A. Refahi Oskouei
Keyword(s):  
Acoustic Emission ◽  
Composite Materials ◽  
Failure Modes ◽  
Composite Plates ◽  
In Situ Monitoring ◽  
Buckling Loads ◽  
Emission Monitoring ◽  
Initiation And Propagation ◽  
Scanning Electron

Delamination and Fracture are the most common failure modes in composite materials, since they will result in the reduction of stiffness and can grow throughout other layers. Buckling is consisted of two main stages including delamination and fracture. Delamination is too consisted of two main stages including initiation and propagation. AE is a suitable method for in situ monitoring of damage in composite materials. In this study, by using AE monitoring, an experimental analysis on different sets of glass/polyester under buckling loading has been carried out. Scanning electron microscope (SEM) was used in thistest to show behavior of the initiation delamination damage.

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