Presentation fatigue

8/10/2019 Presentation fatigue

1/22

SEMINAR PRESENTATION ON

Fatigue on engine pistons

A compendium of casestudies

by

M.V.RAVI KIR


2/22

Abstract Engine pistons are one of the most complex components am

automotive or other industry field components. The engine

called the heart of a car and the piston may be considered timportant part of an engine.

There are lots of research works proposing, for engine pistothere are huge number of damaged pistons.

Damage mechanisms have different origins and are mainly w

temperature, and fatigue related. Among the fatigue damagthermal fatigue and mechanical fatigue, either at room or attemperature , play a prominent role.

This work is concerned only with the analysis of fatigue-dampistons.


3/22

Pistons from petrol and diesel engines,from automobiles, mand trains will be analyzed.

A compendium of case studies of fatigue-damaged pistons ipresented.

A fractographic study is carried out in order to confirm cracksites.


4/22

Introduction Piston may be considered the heart of an engine. piston is one o

stressed components of an entire vehicle.

As one of the major moving parts in the power transmitting assthe piston must be so designed that it can withstand the extrempressure of combustion.

Piston also aids in sealing the cylinder to prevent the escape of cgases.

As it is the main components in an engine, pistons technological

is expected to continue and they are expected to be more and mstronger , lighter, thinner and durable.

The pistons form the bottom half of the combustion chamber antransmits the force of combustion through the wrist pin and conrod to the crankshaft.


5/22

There are many significant number of damaged pistons.

Damages may have different origins: mechanical stresses , tstresses , wear mechanisms , temperature degradation etc.

Fatigue is a source of piston damages. Cyclic stresses have mainly two origins : load and temperatu

Traditional mechanical fatigue may be the main damaging min different parts of a piston depending on different factors.

High temperature fatigue is also present in some damaged p

In this work, different pistons, from different kinds of engineengines; motorcycle engines; and automotive engines will bpresented.


6/22

FATIGUE DAMAGED PISTON

Mechanical and hightemperature

mechanical damagedpistons.

Thermal and tmechanical da

pistons.

EXPERIMENTAL WORK


7/22

Mechanical and high temperaturemechanical fatigue

Damaged areas

Piston head andpiston pin holes

Pistoncompression

Ring grooves

Pisto


8/22

Piston head and piston pin hole

Typical engine piston Typical stress distribution on an engine p


9/22

Fractographic analysis

Petrol engine piston with a crack from one side of the pin hole

to the head


10/22


11/22

Linear static stress distribution of pis


12/22

Piston compression grooves

The striations clearly show the propagation of the crack


13/22

Typical stress distribution on stress radius on the grooves


14/22

piston skirt

Engine piston with damaged skirt


15/22

Typical stress distribution on engine skirt with a big clearance


16/22

Thermal/thermal mechanical fatigue

Thermal fatigue is related to the stresses in the material indthermal gradients in the component.

In a piston thermal stresses are due to

(a) The vertical distribution of the temperature along the pisttemperatures at the top and lower temperatures at the bo

(b) the different temperatures at the head of the piston due tof the hot gases or to fuel impingement.


17/22

(a) Thermal stresses due to the vertical distribution

(b) Thermal stresses due to the different temperatures atthe head

of the piston


18/22

Examinations and discussionMechanical fatigue:

Piston head and piston pin hole

Static stresses concentrate mainly at pin holes. But piston starts cracks at head.

Reason for the crack to initiate at that point may be due to two daspects:

Mechanical fatigue:

Crack always initiate at the same points at the same vertical placontains pin holes.

Thermal fatigue does not seem to be the reason for these cracksthermal fatigue produces more than one visible cracks.


19/22

High temperature mechanical fatigue:

Piston head is always hotter than the bottom and pin hole a

If we combine effect of temperature with static stresses, the

two critical areas. This is the biggest of all fatigue damaged pistons.

Piston compression grooves:

Compression ring is the one has the function of not allowingpressure to be lost between piston and cylinder wall.

When clearance between piston and cylinder wall becomes there is an increase of pressure acting on the ring and a streincrease on compression groove.


20/22

Piston skirt:

Piston skirt may break by fatigue and reason are the stressethe curvature radius of some skirt geometries.

Damage may be related to clearance between piston and cywall.

Thermal/thermal-mechanical fatigue:

Thermal fatigue cracks are easy to identify because they usua particular feature.

If they were high temperature mechanical fatigue cracks it wonly one crack and the crack would be located at the verticathat contains the pin hole.


21/22

Proposals and in course solutions This analysis will be divided into five aspects:

Materials

Local reinforcements

Surface coatings

Design

Piston cooling


22/22

conclusions

The first main conclusion that could be drawn from this woralthough fatigue is not the responsible for biggest slice of dapistons, it remains a problem on engine pistons and its solutremains a goal for piston manufacturers and it will last a prolong because efforts on fuel consumption reduction and powincrease will push to the limit weight reduction, that meanswalls and higher stresses.

To satisfy all the requirements with regard to successful apppistons, in particular mechanical and high temperature mecfatigue and thermal/thermalmechanical fatigue there are sconcepts available that can be used to improve its use, suchdesign, materials, processing technologies, etc.

Presentation fatigue

Documents

Transcript of Presentation fatigue