Acoustic emission description from a damage and failure scenario of rotomoulded polyolefin sandwich structure subjected to internal pressure for storage applications

Abstract

The aim of this paper is to study the damage mechanisms in a sandwich polymer structure that contains three layers: two polyolefin skins and the foam core (skin–foam–skin). Specific tests on structure associated with the acoustic emission (AE) technique and tomographic observations (RX) are used to identify the damage. Initially, a conventional tensile test was performed to correlate the acoustic emission with the initiation of plasticity and damage to a polyethylene sample. The results obtained are close to those observed in other studies and it is possible to separate the signal from cavitation and propagation of necking. The technique is then employed to capture the rupture of a polymer skin on a multilayer rotomoulded structure (bottle). Tests were carried out on this bottle under internal water pressure. Three tests are performed with more or less early interruptions in order to identify the first damage and understand their evolution. Different quantities (average frequency, RA value, etc.) are observed in order to quantify and understand the perceived damage. With the AE/RX correlation and mechanical behaviour, a scenario of structural damage is proposed.

Identification of damages into a polymer structure by AE - transition from tensile specimen to structure

“…The bottle is produced with a threaded cap. It is cut by machining at this point to install the clamps that hold and seal the bottle during pressure testing [19]. Tomography of a longitudinal section of the bottle (bottle axis) [19].…”

“…During tests, the four marks are monitored in real time by a CCD camera. The logarithmic (or true) longitudinal (𝜀 𝑙 ) and transverse (𝜀 𝑡 ) strains are calculated with the current and initial distances between longitudinal and transverse (in width direction) marks, and the increments of these values [19][20]. The Cauchy stress in the loading direction (or True stress) is determined from the current axial load, the initial cross-section area of the specimen and the true transverse strain, in isochoric framework and assuming isotropy of true transverse strains (in width and thickness) [19][20].…”

“…The experimental test bench "Endomat" [19,23] is a tri-axial mechanical test machine allowing the following stresses: tension-compression (1200kN), torsion (55kN), and internal pressure (1200bar). In addition, this bench makes it possible to impose mechanical compression and internal pressure on a structure simultaneously.…”

“…The bottles in the initial state are tomographed in order to be compared with the scans taken after each test interruption to correlate these signals to damage. The material and structure are introduced in the following paragraph, and then the experimental systems and the associated acoustic emission technique are detailed in the experimental procedure paragraph [19]. Finally, the paragraph on results and discussion presents the results of the tensile and bottle tests before concluding.…”

Bending Resistance and Failure Type Evaluation of Basalt Fiber RPC Beam Affected by Notch and Interfacial Damage Using Acoustic Emission

“…Non-extended statistical modeling of electrical emissions were used to predict the fracture of mortar beams by Stergiopoulos et al [19]. In addition, as a new non-destructive testing method, AE has been widely used for the damage monitoring of various materials [20] such as marble [21], joint specimens [22], buried pipe deformation [23], and polymer structure [24]. Zhou et al [25] proposed a method to reconstruct the denudation of sedimentary basin by using AE, a technique which is also effective in monitoring the tensile failure mechanism of carbon fiber woven composites [26].…”