PSI - Issue 52

Vitalijs Pavelko et al. / Procedia Structural Integrity 52 (2024) 382–390 Vitalijs Pavelko/ Structural Integrity Procedia 00 (2019) 000 – 000

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destruction of the transducer during extreme overloads. Durable subjecting of variable load causes fatigue cracks in the sensitive elements and their connection to the structure. Aging processes of different nature, corrosion, temperature effect can cause full or partial loss of functional operability of transducers. But the problem of strength and fatigue live of transducers is the most relevant. It is known that piezoceramic is the most popular material of piezoelectrical transducer. Piezoceramic materials have a sufficiently high compressive statice strength (about 600 MPa) and compressive fatigue strength Mizuno et al. (2010), and relatively low strength at tension or bending, about 45 and 80 MPa respectively Tanimoto et al. (1994). The simplest way to avoid sudden destruction or fatigue damage involves the installation of transducers on compressed or weakly loaded stretched sections of the structure. At the same time, to ensure effective detection of structural damage , transducers must be embedded in a structure that is most often exposed to tensile stresses. In any case, the analysis of loading conditions and the estimation of safety of operational load for piezoceramic transducer are required. In the work Bin Lin et al. (2010) the conditions of loss of operability of a typical piezoelectrical transducer (PET) installed on the surface of thin-walled host sample under static and fatigue loads are investigated. The characteristics of static and fatigue strength of square-shaped transducer (7x7 mm) are presented in term of strain of host sample. The paper Meisner, et al. (2014) presents results of durability tests performed using embedded PZT-transducers on composite panels under tensile static and cyclic loading. Different measurement techniques (e.g., measurement of electric charge vs. applied strain) are used to determine sensitive failure indicators of piezoelectrical transducers. In the paper Hu Sun et al. (2018) it is shown the piezoceramic sensors still work well when they are bonded on the host structures with tensile strain up to 4000με by using the optimal adhesive. Another means of PET protection from fatigue is proposed and developed in Pavelko I. et al. (2010 (1), (2)), Pavelko I. (2010). It is based on the creation in the transducer of a field of residual compressive stress. Problems of strength and fatigue of piezoceramics under mechanical and electrical loads are analyzed in Sun (2000), Buethe et al. (2014), and Wandowski et al. (2015). This short overview shows that designing procedure of SHM system should include options for protection of sensitive components of SHM system from intensive degradation and the loss functional operability during established service period. The estimate of the fatigue strength of the rectangular shape PET embedded in the thin-walled Al-panel is presented in this paper based on the test data and FEM analysis of stress state.

Nomenclature Al

aluminium

EFC FEM FEA

equi-fragmental crushing finite element method

finite element analysis FSCT fatigue strength of constrained transducer PET piezoelectrical transducer PZT lead zirconium titanate SHM structural health monitoring

2. Some results of transducers destruction during the fatigue test. Initially, fatigue tests were planned to study the effectiveness of ultrasonic technology of cracks detection in complex structures. However, during the tests, many fatigue cracks were found in piezoelectric transducers (PET) built into the panel as a prototype of the sensitive elements of the structural health monitoring system. Obtained experimental information and analysis of the stress state of the structure with embedded PET, including simulation of their damage, it is useful for assessing the own reliability of the structural health monitoring system. In Fig.1 the picture of an aeronautical panel that contains a 1.015 mm Al-alloy2024-T3 sheet supported by a stringer is presented in the clamps of test machine. The dimensions of the working part of the panel are equal: width 200 mm, length 380 mm. Stringer is manufactured as the thin-walled Al-alloy bar of standard angular cross-section 20x20x1.5