Failure analysis of a special vehicle engine connecting rod

This paper presents failure analysis of the connecting rod used in a 12-cylinder diesel engine set on a special vehicle. The fracture of the connecting rod occurred during the engine test in laboratory conditions. Chemical and metallographic analysis as well as mechanical testing have confirmed that the material properties of the connecting rod met the requirements of standard specification and technical documentation. Linear finite element (FE) analysis was performed to evaluate stress state of the connecting rod under maximum load. The results of FE analysis showed that the position of the fracture is consistent with the zone of highest stress. Fractographic analysis has not been able to reveal the main cause of mechanism of fracture due to substantially damaged fracture surface. Inadequate machining, absence of polishing and highest stress in the region of fracture were identified as the main causes of failure. Finally, the engine had been working at maximum load for a longer period of time that also led to the breakage of the connecting rod.This is the peer reviewed version of the paper: Rakić, S. N.; Bugarić, U.; Radisavljević, I.; Bulatović, Ž. Failure Analysis of a Special Vehicle Engine Connecting Rod. Engineering Failure Analysis 2017, 79, 98–109. [https://doi.org/10.1016/j.engfailanal.2017.04.014

Ballistic Behaviour of Austempered Compacted Graphite Iron Perforated Plates

In this study, the performance of austempered compacted graphite iron was evaluated to find its suitability as perforated plates used in add-on armour. Perforated compacted graphite plates were subjected to austenitisation at 900 degrees C for 2 h followed by austempering at 275 and 400 degrees C for 1 h. The basic plate was fixed at 400 mm away from the perforated plate and armour and then piercing incendiary projectile was shot from a distance of 100 m. It was observed that both 7 mm and 9 mm perforated plates austempered at lower temperature of 275 degrees C producing higher hardness and lower ductility were effective in fracturing the penetrating core, thereby significantly decreasing the chances of penetrating the basic plate

Ballistic Behaviour of Austempered Compacted Graphite Iron Perforated Plates

In this study, the performance of austempered compacted graphite iron was evaluated to find its suitability as perforated plates used in add-on armour. Perforated compacted graphite plates were subjected to austenitisation at 900 °C for 2 h followed by austempering at 275 and 400 °C for 1 h. The basic plate was fixed at 400 mm away from the perforated plate and armour and then piercing incendiary projectile was shot from a distance of 100 m. It was observed that both 7 mm and 9 mm perforated plates austempered at lower temperature of 275 °C producing higher hardness and lower ductility were effective in fracturing the penetrating core, thereby significantly decreasing the chances of penetrating the basic plate

Analysis of impact toughness and the critical stress intensity factor KIc in ferrite-austenite welded joints with different heat input

Introduction/purpose: Constructions always have several critical points that can be sources of possible defects. All these critical places must be taken into account in safety assessment where the most unfavorable exploitation factors are considered and the local safety of a joint is assessed. Today, joints of various compositions are becoming more frequent in metal constructions. Due to the requirements of economy and ecology, welded joints of microalloyed ferritic steels with high-alloyed austenitic steels are increasingly encountered during the construction of power plants, chemical facilities, etc. Tests of such welded joints have been performed on tanks for oil derivatives, where parts of the tank shell are made of microalloyed ferritic\ud steel and the roof structure is made of high-alloyed austenitic steel. Methods: In the paper, an experimental analysis of crack propagation in an austenitic-ferritic welded joint was performed. The welding was performed by the MIG welding process with two different heat inputs, and the same filler material MIG 18/8/6 was used. Two types of welded plates were tested. The characteristics of the base, filler and auxiliary materials and welding technologies are given. Notched test specimens with an initiated crack-type fracture were made in order to determine the impact properties and fracture mechanics parameters. The results: The research carried out within this study aimed to compare the obtained results of the impact toughness and fracture toughness at flat deformation in a ferrite-austenitic welded joint. An evaluation of the results obtained during the testing of the experimental plates welded with different amounts of heat input is also given. Conclusion: These test results established the dependence of the geometry of a propagating crack and the stress conditions for further crack propagation. It is possible to determine the values of the parameters that describe the behavior of the material, both in linear-elastic and in elastoplastic fracture mechanics

Investigation of mechanical failure cause of an aircraft piston engine cylinder head

Tokom leta školskog aviona Utva-75 došlo je do otkaza motora usled pucanja glave cilindra. Nakon uspešno izvršenog prinudnog sletanja oštećeni sklop cilindra je demontiran sa motora aviona i poslat na forenzičku ekspertizu. Fraktografskim ispitivanjem prelomne površine utvrđeno je da je uzrok otkaza zamor materijala glave cilindra. Metalografska ispitivanja pokazala su da je uzrok nastanka zamorne prsline postojanje značajne poroznosti materijala upravo u zoni nastanka loma. Numerička simulacija naponskog stanja sklopa cilindra, izvršena metodom konačnih elemenata, potvrdila je pretpostavku da je lom iniciran u zoni najveće koncentracije napona.The piston engine of the training aircraft Utva-75 malfunctioned during the flight mission due to the cracking of its cylinder head. After successful forced landing, the damaged cylinder assembly was removed from the engine and sent to the lab for forensic expertise. Fractographic examination of the mating fracture surfaces revealed that the fatigue was the main cause of the cylinder head failure. The metallography examination has shown that the fatigue was promoted from pre-existing material defect due to an elevated presence of porosity forms at the crack initiation zone. The finite element method, utilized to determine the stress state of the cylinder assembly, confirmed that the crack origin was located at the most stress area

Investigation of mechanical failure cause of an aircraft piston engine cylinder head

Tokom leta školskog aviona Utva-75 došlo je do otkaza motora usled pucanja glave cilindra. Nakon uspešno izvršenog prinudnog sletanja oštećeni sklop cilindra je demontiran sa motora aviona i poslat na forenzičku ekspertizu. Fraktografskim ispitivanjem prelomne površine utvrđeno je da je uzrok otkaza zamor materijala glave cilindra. Metalografska ispitivanja pokazala su da je uzrok nastanka zamorne prsline postojanje značajne poroznosti materijala upravo u zoni nastanka loma. Numerička simulacija naponskog stanja sklopa cilindra, izvršena metodom konačnih elemenata, potvrdila je pretpostavku da je lom iniciran u zoni najveće koncentracije napona.The piston engine of the training aircraft Utva-75 malfunctioned during the flight mission due to the cracking of its cylinder head. After successful forced landing, the damaged cylinder assembly was removed from the engine and sent to the lab for forensic expertise. Fractographic examination of the mating fracture surfaces revealed that the fatigue was the main cause of the cylinder head failure. The metallography examination has shown that the fatigue was promoted from pre-existing material defect due to an elevated presence of porosity forms at the crack initiation zone. The finite element method, utilized to determine the stress state of the cylinder assembly, confirmed that the crack origin was located at the most stress area

Influence of welding parameters on joint properties of friction stir welded aluminum alloys

У раду је испитан УТИЦАЈ ПАРАМЕТАРА ЗАВАРИВАЊА НА СВОЈСТВА ЗАВАРЕНИХ СПОЈЕВА АЛУМИНИЈУМСКИХ ЛЕГУРА ДОБИЈЕНИХ ПОСТУПКОМ ЗАВАРИВАЊА ТРЕЊЕМ АЛАТОМ. Коришћене су две комерцијалне алуминијумске легуре, 5052-Н32 и 2024-Т351, које су испоручене као плоче дебљљине 8mm. Како би се оценио утицај унете енергије на понашање материјала и квалитет завареног споја у раду су варирани параметри заваривања, при чему се однос брзине ротације и брзине заваривања (Vrot/Vzav) кретао од 3,16 до 51,30. Брзина ротације алата износила је 450, 600, 750, 950, 1180 и 1500 obr/min а брзина заваривања је варирана је од 23 до 380 mm/min. Угао нагиба алата износио је 10. Сматра се да однос Vrot/Vzav указује да ли је за дате параметре заваривања могуће добити спој без присуства грешака, али не и какве ће он механичке карактеристике поседовати. Резултати ове дисертације указују да се на основу овог односа може само оријентационо претпоставити понашање споја. Иако се иста или приближно иста вредност односа Vrot/Vzav може остварити применом различитих параметара заваривања (нпр. 1180/116=10,17; 950/93=10,21; 750/73=10,27), добијени резултати дају основу да се претпостави да се услови одигравања процеса заваривања и формирања споја феноменолошки разликују. Поред односа Vrot/Vzav, велику улогу у добијању споја задовољавајућег квалитета има величина и константност притисне силе у вертикалном правцу. Повећање брзине ротације алата (Vrot) има позитиван утицај на механичке карактеристике завареног споја. Смањење брзине заваривања проузрокује деградацију изгледа површине споја услед прегоревања материјала. Смањење брзине заваривања има позитивног ефекта на повећање величине угла савијања при коме долази до појаве прслине. Резултати одређивања енергије удара указују да смањење брзине заваривања позитивно утиче на повећње жилавост споја. Са друге стране при Vrot=1180 obr/min са смањењем брзине заваривања долази до...INFLUENCE OF WELDING PARAMETERS ON JOINT PROPERTIES OF FRICTION STIR WELDED ALUMINUM ALLOYS was studied in this work. Two commercial Al alloys 5052-Н32 and 2024-Т351 were received as 8 mm thick plates. In order to evaluate the influence of heat input during welding on alloys behavior and properties of weld joint, welding parameters were varied in broadly. Achieved ratio between rotation and welding speed was between 3,16 and 51,30, i.e. rotation rate was 450, 600, 750, 950, 1180 and 1500 rev/min, while welding speed was between 23 and 380 mm/min. The pin angle was 10. The welded joints were tested by means of both non-destructive (visual, penetrant and X-ray inspection) and destructive (metallographic, tension and hardness) testing. In all specimens typical zones are revealed, with corresponding differences in grain size. The obtained results suggested that weld appearance was more affected by rotation rate than by welding speed, due to differences in generated heat level. Increasing R/v ratio leads to higher, both, heat input (expressed as pseudo-heat index R2/v) and stirring increment, implying that the behavior is not uniform. Furthermore, it can be assumed that welding parameters and material flow have combined effect on weld appearance and they cannot be taken into consideration separately. Increasing R/v ratio leads to greater size of weld nugget—width and depth. This is due to a higher heat input and stirring increment owing to increased R/v ratio. Note that higher heat input improves material flow around tool pin. In other words, ‘‘revolutions per one millimeter’’ of the weld metal is increased by increasing R/v ratio. Therefore, a large amount of frictional heat and plastic-work are produced, and thus material easily flows and bigger NZ is formed. Different spacing between rings is related to the pin forward movement per revolution, i.e., at a rotation rate of 750 and 1180 r/min and welding speed of 116 mm/min. The grain size revealed in the NZ and part of TMAZ is very fine. It is expected that, during very intensive deformation at high temperature, grain refinement is introduced by both deformation and recrystallization (static or even..

Influence of welding parameters on joint properties of friction stir welded aluminum alloys

У раду је испитан УТИЦАЈ ПАРАМЕТАРА ЗАВАРИВАЊА НА СВОЈСТВА ЗАВАРЕНИХ СПОЈЕВА АЛУМИНИЈУМСКИХ ЛЕГУРА ДОБИЈЕНИХ ПОСТУПКОМ ЗАВАРИВАЊА ТРЕЊЕМ АЛАТОМ. Коришћене су две комерцијалне алуминијумске легуре, 5052-Н32 и 2024-Т351, које су испоручене као плоче дебљљине 8mm. Како би се оценио утицај унете енергије на понашање материјала и квалитет завареног споја у раду су варирани параметри заваривања, при чему се однос брзине ротације и брзине заваривања (Vrot/Vzav) кретао од 3,16 до 51,30. Брзина ротације алата износила је 450, 600, 750, 950, 1180 и 1500 obr/min а брзина заваривања је варирана је од 23 до 380 mm/min. Угао нагиба алата износио је 10. Сматра се да однос Vrot/Vzav указује да ли је за дате параметре заваривања могуће добити спој без присуства грешака, али не и какве ће он механичке карактеристике поседовати. Резултати ове дисертације указују да се на основу овог односа може само оријентационо претпоставити понашање споја. Иако се иста или приближно иста вредност односа Vrot/Vzav може остварити применом различитих параметара заваривања (нпр. 1180/116=10,17; 950/93=10,21; 750/73=10,27), добијени резултати дају основу да се претпостави да се услови одигравања процеса заваривања и формирања споја феноменолошки разликују. Поред односа Vrot/Vzav, велику улогу у добијању споја задовољавајућег квалитета има величина и константност притисне силе у вертикалном правцу. Повећање брзине ротације алата (Vrot) има позитиван утицај на механичке карактеристике завареног споја. Смањење брзине заваривања проузрокује деградацију изгледа површине споја услед прегоревања материјала. Смањење брзине заваривања има позитивног ефекта на повећање величине угла савијања при коме долази до појаве прслине. Резултати одређивања енергије удара указују да смањење брзине заваривања позитивно утиче на повећње жилавост споја. Са друге стране при Vrot=1180 obr/min са смањењем брзине заваривања долази до...INFLUENCE OF WELDING PARAMETERS ON JOINT PROPERTIES OF FRICTION STIR WELDED ALUMINUM ALLOYS was studied in this work. Two commercial Al alloys 5052-Н32 and 2024-Т351 were received as 8 mm thick plates. In order to evaluate the influence of heat input during welding on alloys behavior and properties of weld joint, welding parameters were varied in broadly. Achieved ratio between rotation and welding speed was between 3,16 and 51,30, i.e. rotation rate was 450, 600, 750, 950, 1180 and 1500 rev/min, while welding speed was between 23 and 380 mm/min. The pin angle was 10. The welded joints were tested by means of both non-destructive (visual, penetrant and X-ray inspection) and destructive (metallographic, tension and hardness) testing. In all specimens typical zones are revealed, with corresponding differences in grain size. The obtained results suggested that weld appearance was more affected by rotation rate than by welding speed, due to differences in generated heat level. Increasing R/v ratio leads to higher, both, heat input (expressed as pseudo-heat index R2/v) and stirring increment, implying that the behavior is not uniform. Furthermore, it can be assumed that welding parameters and material flow have combined effect on weld appearance and they cannot be taken into consideration separately. Increasing R/v ratio leads to greater size of weld nugget—width and depth. This is due to a higher heat input and stirring increment owing to increased R/v ratio. Note that higher heat input improves material flow around tool pin. In other words, ‘‘revolutions per one millimeter’’ of the weld metal is increased by increasing R/v ratio. Therefore, a large amount of frictional heat and plastic-work are produced, and thus material easily flows and bigger NZ is formed. Different spacing between rings is related to the pin forward movement per revolution, i.e., at a rotation rate of 750 and 1180 r/min and welding speed of 116 mm/min. The grain size revealed in the NZ and part of TMAZ is very fine. It is expected that, during very intensive deformation at high temperature, grain refinement is introduced by both deformation and recrystallization (static or even..

Eliminacija tunela pri zavarivanju trenjem alatom legure Al 5052-H32

Some experiences in elimination of tunnel type defect Friction Stir Welding of Al alloy 5052-H32 are presented in this paper. In order to evaluate the influence of the processing parameter (ratio between rotation and translation speed during welding) on the occurrence of tunnel type defects and quality of welded joint, different welding parameters were varied. Welded joints were tested by means of both nondestructive (visual inspection, X-ray inspection) and destructive (metallographic, bending, tension and hardness) testing. Best results were obtained for the ratio between 6.45 and 8.22. Results suggest that with this ratio, the material flows around the pin with optimal speed, i.e. sufficient amount of material is available to fulfill the gap and prevent tunnel formation.U radu su predstavljena iskustva na eliminaciji greške tunela u zavarenim spojevima dobijenih zavarivanjem ploča postupkom zavarivanja trenjem alatom na leguri Al 5052-H32. U cilju određivanja uticaja parametara zavarivanja (odnos brzine rotacije alata i brzine zavarivanja-translacije) na pojavu greške tunela i kvalitet zavarenog spoja, parametri su varirani u širokom opsegu. Zavareni spojevi su ispitivani metodama bez razaranja (vizuelno, penetrantima i rentgenski) i sa razaranjem (metalografski, zatezanje, tvrdoća i savijanje). Zavareni spojevi sa najboljim osobinama postignuti su kod spojeva zavarenih korišćenjem odnosa u opsegu od 6.45 do 8.22. Rezultati ukazuju da su to odnosi koji obezbeđuju optimalni način tečenja materijala oko trna alata, tj. da je kontinuirani dotok materijala na povratnu stranu dovoljan da homogeno popunjava prazninu i spreči pojavu kanala

The effect of friction stirs welding speed on microstructure, mechanical properties and IGC of EN AW-5083 plates

The aim of this work was to evaluate the influence of welding speed on microstructure, mechanical properties, as well as Intergranular corrosion (IGC) susceptibility of EN AW-5083 alloy welded using FSW. FSW was performed using constant rotation speed of 750 Rev/min, while welding speed was varied from 73 mm/min, 150 mm/min to 190 mm/min. Results show that increase of welding speed lead to decrease of the size of the nugget. This behavior is attributed to decrease of heat input during welding. Accordingly, lower grain size provides increase of the strength. All tested welds are resistant to IGC, evaluating by mass loss according to NAMLT test, and resistivity slightly decrease with increasing welding speed