Integrity assessment of ammonia spherical storage tank

The integrity of the ammonia spherical tank (with a volume of 1800 m3 and the outer diameter of 15120 mm, nominal wall thickness 30 mm) was analyzed due to discovered cracks on the longitudinal and transverse but joints of the segments, of different lengths and depth. The calculation according to EN 13445-3: 2014 specifies the minimum required spherical shell wall thickness. The finite element method was used to analyze the cracks and determine the hoop stress value. The stress intensity factor for the analysed cracks was analytically determined, and the obtained values were compared with the critical value of the stress intensity factor to assess the integrity of the observed structure

Composite material selection for aircraft structures based on experimental and numerical evaluation of mechanical properties

In this paper determination of mechanical properties of composite material using experimental and numerical approach is presented. The mechanical properties of a laminate obtained in the experiment are used for verification of numerically obtained values, as well as estimation of the load-carrying capacities of composite engine cover of light aircraft. Composite specimens, consisting of epoxy matrix and glass fibers with orientation angles 0 degrees, 45 degrees, and 90 degrees, have been made according to standards, and the mechanical properties were investigated in tensile and three-point bending tests. The tensile strength, bending strength, elasticity modulus, strain, and force at laminate failure have been evaluated and then compared to values obtained in numerical simulations with the aim of verifying the FE model used for failure prediction of structural laminates. Good agreement of experimental and numerical values provides a solid foundation for further improvements of the numerical model

Impact of temperature and exploitation time on plane strain fracture toughness, k-ic, in a welded joint

This paper presents the analysis of the impact of temperature and exploitation time on the tendency toward brittle fracture of welded joint constituents of new and exploited low-alloyed Cr-Mo steel A-387 Gr. B, by using fracture mechanics parameters. The exploited parent metal is a part of the reactor mantle which has been in service for over 40 years and is in the damage repair stage, i.e. in the stage where a part of the mantle is being replaced with new material. Testing of the fracture toughness at plane strain is done in order to determine critical value of stress intensity factor, K-Ic, i.e. evaluation of behaviour of new and exploited parent metal (PM), weld metal (WM) and heat affected zone (HAZ). Based on the testing results, the analysis of tendency to brittle fracture represents the comparison of the obtained values for characteristic areas of the welded joint and the justification of selected welding technology

Impact of temperature and exploitation time on plane strain fracture toughness, k-ic, in a welded joint

This paper presents the analysis of the impact of temperature and exploitation time on the tendency toward brittle fracture of welded joint constituents of new and exploited low-alloyed Cr-Mo steel A-387 Gr. B, by using fracture mechanics parameters. The exploited parent metal is a part of the reactor mantle which has been in service for over 40 years and is in the damage repair stage, i.e. in the stage where a part of the mantle is being replaced with new material. Testing of the fracture toughness at plane strain is done in order to determine critical value of stress intensity factor, K-Ic, i.e. evaluation of behaviour of new and exploited parent metal (PM), weld metal (WM) and heat affected zone (HAZ). Based on the testing results, the analysis of tendency to brittle fracture represents the comparison of the obtained values for characteristic areas of the welded joint and the justification of selected welding technology

Composite material selection for aircraft structures based on experimental and numerical evaluation of mechanical properties

In this paper determination of mechanical properties of composite material using experimental and numerical approach is presented. The mechanical properties of a laminate obtained in the experiment are used for verification of numerically obtained values, as well as estimation of the load-carrying capacities of composite engine cover of light aircraft. Composite specimens, consisting of epoxy matrix and glass fibers with orientation angles 0 degrees, 45 degrees, and 90 degrees, have been made according to standards, and the mechanical properties were investigated in tensile and three-point bending tests. The tensile strength, bending strength, elasticity modulus, strain, and force at laminate failure have been evaluated and then compared to values obtained in numerical simulations with the aim of verifying the FE model used for failure prediction of structural laminates. Good agreement of experimental and numerical values provides a solid foundation for further improvements of the numerical model

FEM simulation of welded joint geometry influence on fatigue crack growth resistance

Fatigue behaviour of welded joints is investigated, in terms of welded joint geometry and the fatigue crack position. It is based on previous work which involved numerical simulation of fatigue crack growth in a welded joint made of micro-alloyed, low-carbon pressure vessel steel P460NL1, with the main focus on fatigue crack growth rate through different welded joint regions. The goal here was to change the size of the heat affected zone, as the region in which the fatigue crack initiated, and to compare the results obtained for new crack length values with the original ones, obtained by creating numerical models based on experimental data. A number of models were created, some of which simulated the case with a bigger heat affected zone (and, consequently, a smaller crack length in the weld metal), and other which simulated the case with a smaller heat affected zone. Due to the micro-structural differences between these two welded joint regions, noticeable differences appeared in the numbers of cycles obtained for each zone with varying fatigue crack lengths, as well as in the total number of cycles for both zones through which the crack propagated

Crack growth analysis in friction stir welded joint zones using extended finite element method

U ovom radu je prikazana analiza rasta prsine u zonama zavarenog spoja izvedenog postupkom frikcionog zavarivanja mešanjem (FSW). Ploče od legure aluminijuma 2024-T351 su sučeono zavarene primenom postupka FSW. Ploče su modelirane primenom softvera ABAQUS. Osobine materijala u zonama zavarenog spoja su prihvaćene iz radova drugih autora. Ploča je podvrgnuta zamornom opterećenju zatezanjem sa faktorom nesimetričnosti ciklusa R = 0. Rast prsline je praćen (za nestacionarnu prslinu) i faktori intenziteta napona su analizirani u okolini vrha prsline za svaki front prsline. Proširena metoda konačnih elemenata (XFEM) u ovoj analizi je omogućila automatsku generaciju mreže oko vrha prsline kod svakog koraka tokom njenog rasta. Cilj ovog rada je procena integriteta konstrukcije sa inicijalnom prslinom, dobijene frikcionim zavarivanjem mešanjem.Presented in this paper is the analysis of crack growth in zones of a welded joint, obtained by Friction Stir Welding - FSW. Plates of aluminium alloy 2024-T351 are frontally welded using the FSW procedure. Plate models are made using ABAQUS software. Material properties in the weld zones are adopted from papers by other authors. The plate is subjected to tensile fatigue loading with cycle asymmetry factor of R = 0. The crack growth is observed (for a non-stationary crack) and stress intensity factors are analysed around the crack tip for every crack front. The eXtended Finite Element Method (XFEM) in this analysis has enabled automatic mesh generation around the crack tip for every step of its growth. The aim of this paper is the integrity assessment of a structure that is produced by friction stir welding with an initial crack

Application of Fracture Mechanics Parameters to Spherical Storage Tank Integrity Assessment

Fracture mechanics parameters have been applied to assess pressure vessel integrity. The pressure vessel analysed here was the ammonia spherical tank (volume of 1800 m(3), outer diameter 15.12 m, thickness 30 mm) where different cracks in the longitudinal and transverse butt joints were found. The finite element method was used to calculate stress and strain state and to analyse cracks and their influence on spherical storage tank integrity. Toward this end, the stress intensity factors were analytically determined, and compared with the fracture toughness to find out the critical pressure using Failure Assessment Diagram (FAD) in combination with net stress vs. critical stress

Potential for improvement of comfort parameters in off-road vehicles of Serbian Armed Forces

U radu su prikazani usporedni rezultati ispitivanja parametara udobnosti u kabini terenskog automobila Land Rover Defender. Mjerenja su provedena na dvije varijante vozila 110 GS Hard Top i 110 GS Soft Top – heavy duty. Testiranja parametara udobnosti obavljena su samo na vojnim terenskim vozilima, ili još preciznije, na terenskim vozilima koja su u uporabi u Vojsci Srbije. Rezultati obavljenih testiranja nude neke prijedloge za poboljšanje udobnosti vojnih terenskih vozila koja se koriste u Vojsci Srbije. Uspoređeni su elementi udobnosti s aspekta smještaja posade, buke, vibracija i efikasnosti grijanja. Dio eksperimenta je obavljen u realnim eksploatacijskim uvjetima, prilikom intenzivne vožnje terenskih vozila na tri odabrane opitne staze, kako bi se osigurala ponovljivost rezultata ispitivanja: ispresijecana ledina (Deliblatska peščara), ravničarski makadam (Fruška gora) i asfaltna podloga (dionica autoputa Beograd – Zagreb pored Šida zbog manje frekvencije saobraćaja i kvalitetne podloge). Mjerenja buke i vibracija su obavljena na mjestima vozača, suvozača i članova posade pri strogo definiranim brzinama gibanja vozila. Ispitivanje efikasnosti grijanja u kabini obavljeno je u laboratorijskim uvjetima u hladnoj komori poligona Nikinci pri konstantnoj temperaturi okoline od -16 °C.The paper presents the comparative results of comfort parameter testing inside the cabin of Land Rover Defender off-road vehicles. The measurements were carried out on two vehicle models – 110 GS Hard Top and 110 GS Soft Top Heavy Duty. Tests on comfort parameters were performed only on the military off-road vehicles, or to be more precise on the military off-road vehicles used by the Serbian Armed Forces. The results of the performed tests offer some suggestions for the improvement of comfort of military off-road vehicles used by the Serbian Armed Forces.The comfort elements have been compared from the aspect of accommodation of the crew, noise, vibrations and heating efficiency. A part of the experiment was performed by intensive driving of these off-road vehicles in real world conditions, on three pre-selected types of terrain surface, in order to ensure the repeatability of the testing results: heath, gravel and asphalt base (a portion of the Belgrade – Zagreb highway at the territory near Šid was used due to its less frequent traffic and surface quality). Noise and vibration measurements were carried out at the driver’s seat, co-driver’s seat and other passenger seats under strictly defined vehicle speeds. Testing of the heating efficiency inside the cabin was carried out under laboratory conditions in the cold chamber of the artillery range at Nikinci at a constant ambient temperature of -16 °C

Application of Fracture Mechanics Parameters to Spherical Storage Tank Integrity Assessment

Fracture mechanics parameters have been applied to assess pressure vessel integrity. The pressure vessel analysed here was the ammonia spherical tank (volume of 1800 m3, outer diameter 15.12 m, thickness 30 mm) where different cracks in the longitudinal and transverse butt joints were found. The finite element method was used to calculate stress and strain state and to analyse cracks and their influence on spherical storage tank integrity. Toward this end, the stress intensity factors were analytically determined, and compared with the fracture toughness to find out the critical pressure using Failure Assessment Diagram (FAD) in combination with net stress vs. critical stress