THE INFLUENCE OF CORROSION ATTACK ON GREY CAST IRON BRITTLE FRACTURE BEHAVIOUR AND ITS IMPACT ON THE MATERIAL LIFE CYCLE

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1 ACTA UNIVERSITATIS AGRICULTURAE ET SILVICULTURAE MENDELIANAE BRUNENSIS Volume Number 4, THE INFLUENCE OF CORROSION ATTACK ON GREY CAST IRON BRITTLE FRACTURE BEHAVIOUR AND ITS IMPACT ON THE MATERIAL LIFE CYCLE Jiří Švarc 1, Tomáš Binar 1, Petr Dostál 2, Michal Černý 2, Jan Tippner 3 1 Department of Logistics, University of Defence, Brno, Kounicova 65, Brno, Czech Republic 2 Department of Technology and Automobile Transport, Faculty of AgriSciences, Mendel University in Brno, Zemědělská 1, Brno Czech Republic 3 Department of Wood Science, Faculty of Forestry and Wood Technology, Mendel University in Brno, Zemědělská 1, Brno, Czech Republic Abstract ŠVARC JIŘÍ, BINAR TOMÁŠ, DOSTÁL PETR, ČERNÝ MICHAL, TIPPNER JAN The Influence of Corrosion Attack on Grey Cast Iron Brittle Fracture Behaviour and its Impact on the Material Life Cycle. Acta Universitatis Agriculturae et Silviculturae Mendelianae Brunensis, 65(4): The paper is concerned with brittle fracture behaviour of grey cast iron attacked by corrosion and its impact on the life cycle of a spare part made of grey cast iron. In a corrosion chamber, outdoor climatic conditions (temperature and relative air humidity) were simulated in which degradation processes, induced by material corrosion, degrading mechanical properties of a material and possibly leading to irreversible damage of a machine component, occur in the material of maintenance vehicles that are out of operation for the period of one year. The corrosion degradation of grey cast iron, which the spare parts constituting functional parts of an engine are made of grey cast iron, is described with regard to brittle fracture behaviour of the material. For the description of corrosion impact on grey cast iron, an instrumented impact test was employed. A corrosion degradation effect on grey cast iron was identified based on measured values of total energy, macro plastic deformation limit, initiation force of unstable crack propagation and force exerted on unstable crack arrest. In the first part of the experiment, a corrosion test of the material concerned was simulated in a condensation chamber; in the second part of the experiment, research results are provided for the measured quantities describing the material brittle fracture behaviour; this part is supplemented with a table of results and figures showing the changes in the values of the measured quantities in relation to test temperatures. In the discussion part, the influence of corrosion on the values of unstable crack initiation and arrest forces is interpreted. In the conclusion, an overview of the most significant research findings concerning the impact of corrosion on the life cycle of grey cast iron material is provided. Keywords: corrosion attack, brittle fracture behaviour, plastic deformation limit, crack initiation force, crack arrest force, life cycle. INTRODUCTION In the paper, the corrosion impact on the life cycle of maintenance vehicles is described by evaluating its effect on the quantities of material brittle fracture behaviour. One of the special vehicles commonly used in maintenance is TATRA 815 (Binar et al., 2015). The evaluation of the corrosion impact on the life cycle (Dostal et al., 2011) concentrated on an engine cylinder liner above the engine piston, where condensation of moisture can be expected during long term parking (Sukac et al., 2015; Binar et al., 2015). Together with temperature, the condensation can cause the occurrence and development of the adverse effect of corrosion. In metallic materials, corrosion creates a layer of oxides in the initial phase; the corrosion then spreads to the material core in an intercrystalline or transcrystalline manner or as a combination of both. The goal of the research was to evaluate the influence of corrosion attack on the values of 1295

2 1296 Jiří Švarc, Tomáš Binar, Petr Dostál, Michal Černý, Jan Tippner 1: Microstructure of a test specimen 200x zoom macro plastic deformation in the material, a cylinder liner is made of grey cast iron (Joska et al., 2010; Kazda, 2015). As cracking cannot be controlled or influenced under the brittle fracture behaviour of the material, such behaviour ranks among the most dangerous behaviours, and stands behind a number of accidents. The experiment was conducted at test temperatures ranging from 80 to +100 C in order to provide the most apt model of operating conditions, parked vehicles are exposed to throughout the year. The assessment did not take the engine service load into consideration. Temperature range has been extended compared to the real case. Experimental programme A microstructure analysis was conducted on metallographic specimens using an optical microscope. In the metallographic analysis, microstructure formed by ferritic pearlitic primary phase (A in Fig. 1) and graphitic eutectic (B in Fig. 1) was identified (Fig. 1). Corrosion testing was conducted in ZKO 1, K 300 condensation chamber, as per ČSN and ČSN (Dostal and Communeau, 2014). The test specimens were designed for the evaluation of the corrosion impact on brittle fracture characteristics identified at low temperatures (from 0 C to 80 C) and positive temperatures (from +20 C to +100 C) that parked vehicles might be exposed to due to climatic changes throughout the year (Binar et al., 2014). For the sake of more qualitative evaluation of the corrosion impact on the test material, the testing was also performed at extremely low temperatures (approx. 80 C), which are not expected in the climate of the Czech Republic, but theoretically contribute to a more comprehensive study of brittle fracture in grey cast iron. The test schedule was set to 9 periods with cyclically oscillating temperature, humidity and condensation, without gas pollution, which theoretically represents outdoor parking of a vehicle for the period of 1 2 years. One period equals twenty four hours comprising eight hours in the chamber at 43 ± 2 C and 100 % relative humidity and sixteen hours outside the test chamber in a room with a pure atmosphere at 23 ± 2 C and maximum 75 % relative humidity. In order to identify the brittle fracture characteristics of macro plastic deformation limit Fqy, initiation force of unstable crack propagation Fiu, unstable crack arrest force Fa and the total energy Wt, an impact test on RKP 450 iwi instrumented impact tester with nominal energy 300 J was used. For the experiment, test specimens sized ( ) mm, with a V notch 2 mm deep, 45 in angle and the radius of the notch root ρ = 0.25 mm were manufactured from a functional part of the engine, i.e. an engine cylinder liner. V notch was formed from the inner part of the engine cylinder insert (where the piston of the motor is moving) and it was assumed that the notch would be the initiator of the corrosion propagation in the test body. The quantities were measured between 80 C and +100 C, which reflected possible outdoor temperatures parked vehicles are exposed to. Measuring at lower temperatures was conducted using a cooling medium consisting of liquid nitrogen and spirit. Measurements at elevated temperatures were taken in LAUDA PROLINE RP 1290 thermostatic bath. The measurements were conducted as per standards ISO 14556:2000, EN :1990. RESULTS AND DISCUSSION Measured values of the corrosion impact on the material characteristics describing brittle fracture behaviour of grey cast iron is provided in Table 1. The corrosion effect after corrosion testing was only examined visually (refer to Fig. 2); in all examined specimens, the layer of oxides on the material surface only formed localised

3 The Influence of Corrosion Attack on Grey Cast Iron Brittle-Fracture Behaviour and its Impact 1297 I: Values of brittle fracture characteristics quantities Specimen Test temperature Fqy Fiu Fa Wt [ C] [N] [N] [N] [J] : Specimens after 9 cycles of corrosion testing spots, i.e. not a continuous layer of corrosion products. The evaluation of the corrosion impact on macro plastic deformation limit values Due to a low dispersion of macro plastic deformation limit values (Fig. 3) in the examined range of test values, it may be stated that the corrosion effect did not considerably influence the Fqy quantity. The course of Fqy values showed certain changes at 20 C, +40 C and +100 C. Presumably, at lower test temperatures, the macro plastic deformation limit values are higher, and decrease with increasing test temperature in consequence of an energetic support caused by the growing temperature. The evaluation of the corrosion impact on the measured quantities characterising brittle fracture behaviour of grey cast iron When evaluating the corrosion effect on the measured quantities (Fiu, Fa,Wt) at positive test temperatures, considerable decrease was identified at +40 C as against the values from +60 C. The course of measured quantities is linear from +60 C to +100 C (Tab. I). As to the impact on the life cycle of the material, engine cylinder liners are made of, shortening of the engine cylinder liners service life can be assumed at and below 0 C and at +40 C (Fig. 5), judging from the measured values shown in Figs. 1 and 2. At these temperatures, the values of unstable crack propagation initiation and arrest forces decrease considerably in consequence of the corrosion attack lasting for 9 periods. Measurements of the total energy Wt (Tab. I) also proved that the value of energy Wt at the test temperature of 40 C is higher as against the values obtained at 60 C and 20 C. Based on the Wt values measured, a negative effect of corrosion on the material can be assumed at around and below 0 C as against the Wt value at the temperature of +20 C. Even though higher values of total energy Wt, unstable crack propagation initiation force Fiu and arrest force Fa were identified at the test temperature

4 1298 Jiří Švarc, Tomáš Binar, Petr Dostál, Michal Černý, Jan Tippner of 40 C (Fig. 4) as against the values at 60 C (Fig. 5) and 20 C (Fig. 6), formation of places of concentrated stress may be assumed due to lower temperatures and the corrosion effect, causing steeper course of graphs from the test temperature of 60 C and considerable decrease in the measured quantities of Fiu, Fa, and Wt at 60 C (Tab. I). It follows from Fig. 7, representing the relation between the percentage difference of forces at the start and end of unstable crack propagation and test temperature, that with increasing test temperature the difference at the beginning and the end of unstable propagation decreases (on average approx. 59 %). The lower the test temperature is, the greater is the difference in forces at the beginning and the end of unstable crack propagation. For the initiation of unstable crack propagation in the material affected by corrosion at elevated temperatures greater force is required as against negative temperatures. 3: The course for the determination of forces at the test temperature of 40 C 4: The course for the determination of forces at the test temperature of 40 C

5 The Influence of Corrosion Attack on Grey Cast Iron Brittle-Fracture Behaviour and its Impact : The course for the determination of forces at the test temperature of 60 C 6: The course for the determination of forces at the test temperature of 20 C

6 1300 Jiří Švarc, Tomáš Binar, Petr Dostál, Michal Černý, Jan Tippner 7: Difference in unstable crack propagation F iu and F a forces CONCLUSION Experimental measurement has demonstrated the effect of simulating corrosion effect on the reduction of the quantification behavior of a test sample produced from the inner part of the engine cylinder cylinder of the TATRA 815 vehicle (Sukáč et al., 2015). The authors dealt with the influence of characterizing brittle fracture in monography The Impact of Corrosion on the Life Cycle of Military Vehicles (Binar et al., 2016). It follows from the measurements, that there is a high probability of corrosion occurrence in unused maintenance vehicles exposed to changes of temperature throughout the year in the climatic conditions of the Czech Republic. The corrosion degradation effect on the test material leads to the decrease in the measured quantities describing the material brittle fracture behaviour. Considering the fact that the corrosion degradation effect and ambient temperature initiate a decrease in the measured quantities at brittle fracture, and that the crack cannot be controlled, shortening of the life cycle of maintenance vehicles can be assumed. In consequence of irreversible damage to a machine component, the state incurs loss, and unplanned financial means have to be expended on the restoration of the vehicle original properties. Should real climatic conditions of the Czech Republic be considered, temperatures ranging from 0 C to 40 C and from +40 C to + 80 C are to be taken into account out of the measured data set describing the corrosion degradation effect on brittle fracture behaviour of the material. Acknowledgements The work was supported by the Ministry of Defence of the Czech Republic, project No. DZRO K 109. The research has been supported by the project TP 6/2017: Defectoscopic quality assessment of technical and organic materials; financed by IGA AF MENDELU. REFERENCES BINAR, T., DVOŘÁK, I., KADLEC, J., SUKÁČ, J., ROLC, S. and KŘESŤAN, J Material Characteristics of Plastic Deformation in High Strength Steel. Advances in Military Technology, 9(2): BINAR, T., KADLEC, J., REJZEK, M., VLKOVSKÝ, M. and HRUBÝ, V Evaluation of the Test Temperature Effect on Failure Mechanisms and Notched Impact Strength Characteristics of Ultra Hard Low Alloy Steels. Strength of Materials, 43(5): BINAR, T., SUKÁČ, J., ŠILINGER, K., VONDRÁK, J. and KŘESŤAN, J Proving Ultra hard Steel Quality by means of Measuring Ballistic Resistance Influencing the Life Cycle of the Material within a Specific Temperature Range. In: 16th International Conference on Advanced Batteries, Accumulators and Fuel Cells, ABAF USA: Electrochemical Society Inc., p BINAR, T., SUKÁČ, J., ŠILINGER, K., ZATLOUKAL, M. and ROLC, S The Steel Ballistic Resistance Directly Affecting Logistics Related Expenditures. In: 16th International Conference on Advanced Batteries, Accumulators and Fuel Cells, ABAF USA: Electrochemical Society Inc., p

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