SEMINAR –ION

“STUDY ON FATIGUE FAILURE ANALYSIS ON IC ENGINE PISTON”

BY

MR. SANTOSHKUMAR B. BHOYAR

UNDER THE GUIDENCE OF

Prof. R. R. KHARDE

HOD OF MECHANICAL ENGINEERING DEPARTMENT

INTRODUCTION• In IC Engine piston form bottom half part of the combustion chamber and

transmits the force of combustion through the wristpin and connecting rod to the crankshaft.

• Therefore the piston is one of the most important components of an entire vehicles-pressure at the combustion chamber may be reach about 180-200 bar.

• A few years ago this value was common only for heavy –duty truck but now a days it is usual in HDSI

• Piston material and design have evolved over the years and will continue to do so until fuel cells, exotic batteries or something else make the internal combustion engine obsolete.

• As one of the main component in an engine, piston technological evolution is expected to be more. It should be stronger, lighter, thinner and durable for better mechanical efficiency , withstand high pressure.

•Though there has been lot of effort has taken for still their are significant number of damaged piston .•Damaged may have different origin mechanical stress, thermal stresses, wear mechanism, temperature degradation , oxidation mechanism etc.•In this work not only Mechanical fatigue damaged but also Thermo-mechanical fatigue damages are studied.•Fatigue is a sources of piston damages •Fatigue exists when cyclic stresses/deformation occurs in an area on component

GENERAL DISCUSSTION ON FAILURE OF PISTON

• Prior to experimental works. General inspection was that, all piston crown had a combustion pattern resulting from spray pattern of injector nozzles as shown in fig.no.1.1

Fig.1.1 shows a scale formation due to combustion on the piston crown adjacent to the flame heating evidence “petals” as well as on the dome .This may be responsible for fatigue due to cyclic thermal thrust.It is also observed ,all inspected piston had “Nural” markings(Federal Mogul piston brand) It meant that all inspected piston was casted by FM-B2 alloys materials.But adjacent to the wristpin bore, it had found that , there were difference in markings on the piston. This shows that all piston were manufacture to Federal-Mogul specification, but that the pistons were likely to have been manufactured at different time ,at different partner factories. This may be a cause of piston failure due to manufacturing defect.Fig.1.2 highlighting that failure occurred inline with diametric axis of the wristpin.

Fig.1.2 highlighting that failure occurred inline with diametric axis of the wristpin.

MECHANICAL AND HIGH TEMPERATURE FATIGUE ANALYSIS

• Actual root cause of piston failure was studied in experimental work.• In 2006 F.S.Silva had carried out an experimental work on diesel

engine piston and published A compendium of case studies on piston failure in international journal ELSEVIER.

• In his experimental work he discussed about mechanical and high temperature fatigue on piston .

• Mechanical and high temperature fatigue may be divided according to damaged areas.

• Piston head• Piston pin holes• Piston compression grooves• Piston skirt

PISTON HEAD AND PISTON PIN HOLES

• Mechanical fatigue meant that in a piston crack nucleates and propagates in critical stress areas The stresses in this area due to the load acting eternally on the piston because of combustion thrust.

• Fig 4.1 and 4.2 show a typical stress distribution on an engine piston .It is clear that there are two critical areas: The top side of the piston pin hole and two area at the piston head.

• In fractographic analysis shown in fig.4.3 shows that the crack initiated at the pin hole and fig.4.4 and 4.5 shows that crack initiated on the piston head near the combustion chamber.

Fig 4.1 Typical Engine Piston

In fractographic analysis shown in fig.4.3 shows that the crack initiated at the pin hole and fig.4.4 and 4.5 shows that crack initiated on the piston head near the combustion chamber

FEM ANALYSIS

• Fig 4.6 Linear static stress distribution of piston

• Fig 4.6 show that in piston with bowl combustion combustion chamber besides the pin holes their are also two region at the top head where there exist stress concentration. These two area are also located on the same vertical plane that contain pin hole.

PISTON COMPRESSION GROOVES• Typical fatigue damage occurs on piston compression grooves shown in

fig.4.7• The striation clearly show the propagation of crack• Fig.4.8 shows the simulation of stress analysis in piston grooves.• It is clear that there is stress concentration on a stress radius of the groove

when the compression ring is not inside the groove• The inner side of the ring is located at the mid distance of the groove depth.• For compression a simulation of maximum stress with the ring inside the

groove close to the piston wall presented at the maximum stress of the inner side of the of the ring is located at the mid distance of the groove depth.

• Thus there is an exponential growth of the stress when the distance between the ring and the piston wall increases.

• This meant that there is an increase in the stress at the piston groove when the clearance between the piston and the cylinder increases.

PISTON SKIRT• Another common fatigue damage occurs in the piston is related to piston skirt

as shown in fig.4.9• It is clear that the crank start from the curvature radius on the piston skirt.• Fig 4.10 show that ,stress are higher when there is an angle of the piston in

relation to the vertical position • It is important that there must always a clearance between the piston and

the cylinder wall. absences of the clearance the piston never has its up word and down word movement in vertical position also has an angle in relation with cylinder wall.

• It is also clear that the contact point of the piston with cylinder wall are one side of the bottom part of the piston skirts and oppsite side of top part of the piston.

• If the clearance between the piston and cylinder increases the rotation angle also increases and the stress at the piston skirt increases. as shown in fig 4.10

THERMAL AND THERMO-MECHANICAL FATIGUE ANALYSIS

• There are two kind of thermal stress induced in the piston.

• (a) Thermal stress due to the vertical distribution of temperature along the piston- high temperature at the top and lower temperature at the bottom.

• (b) Thermal stress due to the different temperature at the head of the piston due to the flow of the hot gases or to fuel impingement (high pressure injection)

Fig 5.1 Train engine piston with damages head a) Piston 1 b) Piston 2.

Fig 5.3 Schematic thermal distribution at a piston a) Homogenous b) Localized

Fig 5.4. Micrograph of cracked piston

Fig.5.5.Photograf depicting the fracture surface by dashed lines.

Fig.5.6 photograph depicting by the bright appearance of fracture surface of piston.

Fig.5.7.Micrograph depicting the fracture surface by striations on the surface (arrows)

.5.8. Fig micro-graph depicting micro-cracking below combustion bowl lip.

Micrograph depicting the piston crown surface, highlighting the surface erosion connected by

networks of micro-observed during optical microscopy. Pits are cracks emanating from areas of thermal fatigue.

MATERIAL ANALYSISMICOSTRUCTURE

Fig.5.11.Micrograph depicting cracked primary silicon grains adjacent to the crown surface of piston E highlighted by the arrows.

MECHANISM OF FAILURE

Fig.5.12. simulation of failed piston.

Fig.5.13.Critical area of failed piston bowl lip during endurance test cycle.

Fig.5.13. Material strength characteristic with increasing temperature.

Fig.5.14.sketch of mechanism of crack initiation

Discussion and prevention

• Thermo-mechanical overload by insufficient inter cooling.

• Thermo-mechanical overload by over fuelling.• Reduced engine coolant temperature set point• Fuel formulation considerations.• Prevention of future failure.

CONCLUSION

• The fractografic and micro-structural analysis reveled that the pistons were manufactured of normally correct alloys and did not contain significantly deleterious features. The failures were determined to have occurred through the following mechanism:

• Surface thermal damage of the piston bowl lip• Crack initiation by thermal micro-cracking and erosion of

primary particles, leading to threshold flow size• Propagation by thermo-mechanical high and low cycle fatigue.• Brittle fast fracture at critical crack length.• Subsequent fuel and flame impingement resulting in piston

burn through and loss of engine.

THANK YOU