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Monitoring and modelling of propagation paths in cracked solids

Keywords: diagnostics, fracture mechanics, fracture propagation, FRP
Monitoring and modelling of propagation paths in cracked solids - Fig. 1
Fig. 1. Tiles separation in radiant heat floors (Ferretti).
Monitoring and modelling of propagation paths in cracked solids - Fig. 2
Fig. 2. Stress field for masonry wall in shear-test (Ferretti).
Fig. 3. Crack propagation at the interface between fiber reinforced polymer composite and concrete (Carloni).

The monitoring of existing cracks can be performed by means of several non-destructive techniques. A part of the research activity has been dedicated to new techniques for SHM (structural health monitoring), with particular regard to the assessment of externally bonded FRP (fiber reinforced polymer) strengthening systems. The use of FOS (fiber optic sensors) has been taken into account, and some new applications have been developed. A ultrasonic technique has been proposed for detecting defects at the concrete-FRP interface. Defining the crack path numerically is not easy, due to several unknowns: if the direction of crack propagation can be computed by means of one of the existing criteria, it is not known whether this direction will remain constant during crack propagation. A crack initiation leads to an enhanced stress field at crack tip, which propagates into the solid during propagation, locally interacting with the pre-existing stress field. This interaction can lead to modifications of the propagation direction or crack arrest. A numerical code for use with the CM has been developed which returns accurate crack paths for brittle and non-brittle cracks. The CM code has been employed for modelling crack propagation in concrete and masonry.

The main advantage of using the CM for numerical analyses of masonry is that mortar, bricks and interfaces between mortar and bricks can be modelled without any need to use homogenization techniques.

The capability of the CM to handle domains with more than one material has been exploited to capture how the propagation direction changes when the crack overcome the joints or passes from the brick to the interface and to the mortar.

Further, an optical technique known as digital image correlation has been used to monitor the crack initiation and propagation in toughness tests of brittle materials and debonding of composite materials from concrete and masonry.

Main publications

Ferretti E. (2013). A Cell Method Stress Analysis in Thin Floor Tiles Subjected to Temperature Variation. Proc. ICCES’13, International Conference on Computational & Experimental Engineering and Sciences. Seattle, USA. 24-28 May.

Carloni C. and Subramaniam K.V. (2013). Investigation of Sub-Critical Fatigue Crack Growth in FRP/Concrete Cohesive Interface Using Digital Image Analysis. Composites: Part B, 51, 35-43.

Carloni C. and Subramaniam K.V. (2010). Direct Determination of Cohesive Stress Transfer during Debonding of FRP from Concrete. Composite Structures, 93, 184-192.

Daghia F., Giammarruto A., Pascale G. (2009). Monitoring with FBG to control cracking of R.C. structures before retrofitting. In Furuta, Frangopol & Shinozuka. Safety, Reliability and Risk of Structures, Infrastructures and Engineering Systems. LONDON: Taylor & Francis Group (UNITED KINGDOM). 10th International Conference on Structural Safety and Reliability ICOSSAR2009. Osaka. 13-17 September, 1-10.

Ferretti E. (2009). Cell Method Analysis of Crack Propagation in Tensioned Concrete Plates. Computer Modeling in Engineering & Sciences 54, 253-282.

Pascale G., Bastianini F. (2009). The role of quality control and of long-term monitoring in the structural applications of composite materials. In A. Di Tommaso. Meccanica delle strutture in muratura rinforzate con compositi. Bologna: Pitagora (Italy). Convegno Nazionale MURICO3 - Meccanica delle strutture in muratura rinforzate con compositi. Venezia. 22-24 April. 399-406.

Ferretti E., Casadio E., Di Leo A. (2008). Masonry Walls under Shear Test: a CM Modeling. Computer Modeling in Engineering & Sciences 30, 163-190.

Pascale G. (2008). Diagnostica ad ultrasuoni per l'edilizia: strutture civili, beni culturali.

Pascale G. (2007). La valutazione del calcestruzzo nelle strutture esistenti. In Concreto 78, 64-73.

Pascale G., Bonfiglioli B. (2006). Dynamic assessment of reinforced concrete beams repaired with externally bonded FRP sheets. Mechanics of Composite Materials 42, 1-12.

Lanza di Scalea F., Rizzo P., Coccia S., Bartoli I., Fateh M., Viola E., Pascale G. (2005). Noncontact ultrasonic inspection of rails and signal processing for automatic defect detection and classification. Insight 47, No. 6, 346-353.

Strauss A., Bergmeister K., Bonfiglioli B., Pascale G. (2005). Basic Study of Monitoring with FRP. Smart Materials and Structures 14, S12- S23.

Ferretti E. (2004). A Cell Method (CM) Code for Modeling the Pullout Test Step-Wise. Computer Modeling in Engineering & Sciences 6, 453-476.

Ferretti E. (2004). Crack-Path Analysis for Brittle and Non-Brittle Cracks: a Cell Method Approach. Computer Modeling in Engineering & Sciences 6, 227-244.

Stratford T., Pascale G., Manfroni O., Bonfiglioli B. (2004). Shear strengthening masonry panels with sheets. Journal of Composites for Construction 8, No. 5, 434-443.

Research projects

SMooHS – Smart Monitoring of Historical Structures, Unità di Bologna, European Research project ENV.2007.3.2.1.1.