Effects Of Stress-State On Void Coalescence Under Dynamics Loading

Samsul Rizal

Abstract: The influence of the specimen thickness on fracture has been investigated under static loading and interpreted in terms of stress conditions near a crack tip, namely crack tip plasticity under plane strain to plane stress condition. This work investigates the effect of stress conditions on void coalescences pro-duced by impulsive stress intensity of 20, 40? and 80??s duration under one-point bending test, experi-mentally and numerically. The fractographic observation shows that several voids nucleated at inclusions ahead of the crack tip coalescence with each others to form a large void, called a dominant void, and that size of the dominant void decreases as the pulse duration decreases from 40 ?s to 20 ?s, whereas the dominant void is nucleated at the constant distance from the crack tip for plane strain and plane stress condition. Finite element simulations show that the normalized hydrostatic stresses ahead of the crack tip can explain the experimental results that the dynamic fracture toughness of a 10 mm thick specimen tis much smaller than that of a 3 mm thick speciment and that the void nucleation site is independent of the speciment thickness.

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Effect Of Rubber Particle Size Distribution On Fracture Toughness Of Rubber-Modified Polymer Alloys

Husaini

Abstract: This paper describes a numerical study on the effects of the distribution of rubber particles size on the fracture toughness of rubber-modified polymer alloys. FEM analyses were conducted on a deformation field near a crack tip under mode I for a small scale yielding condition. Area near the crack tip is modelled as a composite of matrix materials and rubber particles. On the other hand, the outer region is modelled as a homogeneous material which its constitutive equation has been obtained by analysing a unit cell model of matrix and rubber particle. Perfect bonding or partial debonding of the interface is assumed in the computation. Matrix and rubber particles are treated as Mises and Mooney-Rivlin materials, respectively. It is shown that energy flux into fracture process zone, integral is smaller for bimodal type than monomodal one. This behavior largely occurred on the partial debonding case. These results imply that the screening effects occurred in the bimodal type was larger than monomodal one.

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Pengaruh Penambahan Unsur 0,25 % Mo Pada Besi Tuang Nodular Yang Diaustenisasi Dan Diaustemper Menjadi Austemper Ductile Iron Terhadap Sifat Mekanisnya

Nukman, Bustanul Arifin, Bambang Sugiarto

Abstract: The aim of this research is to investigate the effects of 0.25 % Mo (Molybdenum) which is contained in the ductile cast iron on mechanical properties of Austempered Ductile Iron (ADI). The various temperatures and the holding times are used in the heat treatment processes. Using a given 0.25 % Mo in the ductile iron, ADI’s alloyed developes a higher ultimate tensile stress value and decreases the elongation if we compare with the as cast (non alloy ductile iron). The higher impact energy value obtained at 9000 C austenization and 375o C austempering temperatures during 60 minutes holding times. The structure changes into ausferrit.

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Concept Design And Testing Of Multi-Nozzle Water Mist Fire Suppression Systema

In this work a flexible design of multi-nozzle arrangement of water mist fire suppression system was studied. The source of fire was a 65 mm diameter cooking oil fire. An investigation on the impact of nozzle arrangement on the temperature profile of fires was conducted. The occurance of oil splash due to the application of water mist was also studied. The water mist systems developed in the present work can effectively extinguish cooking oil fires and prevented them from re-ignition. The spray angle, discharge pressure, and water flow rate were important factors to determine the effectiveness of water mist in extinguishing cooking oil fires.

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Hydrogen Absorption Induced Slow Crack Growth In Austenitic Stainless Steels For Petrochemical Pressure Vessel Industries

Type 304L and type 309 austenitic stainless steels were tested either by exposed to gaseous hydrogen or undergoing polarized cathodic charging. Slow crack growth by straining was observed in type 304L, and the formation of α‘ martensite was indicated to be precursor for such cracking. Gross plastic deformation was observed at the tip of the notch, and a single crack grew slowly from this region in a direction approximately perpendicular to the tensile axis. Martensite formation is not a necessary condition for hydrogen embrittlement in the austenitic phase.

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Motor Fuel piston

Combustion piston (piston) consists of a cylinder which equipped with a piston. The piston moves in translation then by the crankshaft is converted into motion spins.

1. Otto Cycle - Gasoline Motor (constant volume air cycle)

A. Motor 4 stroke

Is the motor that requires four times the step piston(twice up and twice down) to obtain one-time effort in the combustion chamber. Step piston motion The succession is:

1. Intake stroke

In this step intake valve open and valve expenditure(exhaust)is closed. Piston function of the TMA to TMB, the volume increases pressure decreases, the fuel + air sucked into the cylinder, but because the cylinder connected with the outside air, so the air pressure on the cylinder at the end of the suction step remains an atmosphere.

2. Compression stroke

In this step the valve intake and exhaust closed. Piston moves from the TMB to the TMA. Fuel + compressed air with the isentropic and the pressure on end of compression of about 7 atm.
The combustion process in which the valve and the intake valves closed and the exhaust air + fuel burned because the electrical spark jumps from the spark plug. this process regarded as the entry process heat.
C8H18 + 12,5      > O2 8 CO2 + 9 H2O + Heat

3. Power stroke

In this step the valve fixed income and expenditure closed. Since the pressure rise due to heat
combustion, resulting in piston driven and generate employment. Piston moves from TMA to the TMB.
The process of heat dissipation, the current intake valve and expenses covered, some of the heat removed through process of radiation, convection and propagation in metallic materials of the cylinder.

4. Step disposal of combustion (exhaust stroke)

In this step intake valve closed and valve open expenditures, piston moves from TMA to TMB crowd out the rest of the combustion on the cylinder and this process occurs at constant pressure.


B. Motor 2 Stroke

Is a machine that required two steps piston (one-time upward / ascending strokes and once to Under / discending stroke) to obtain a one-time businesses in the combustion chamber.

1. Step up

The piston moves upward in the combustion chamber will occurs with the compression and spark jumps electricity to spark plugs, fuel combustion occurs in the space combustion. In the crankcase chamber, with the piston movement upwards, the volume is getting bigger and the pressure becomes smaller than the outside air, so that outside air into the crankcase through the carburetor and there mixing air and fuel in the crankcase.

2. Step down

The piston moves down in the combustion chamber occurs business measures. By the time the piston reaches the hole exhaust (exhaust port), the rest will come out firing and when the piston reaches the hole flushing
(scavenging ports), a mixture of fuel and air from crankcase chamber into the combustion chamber. In the crankcase space volume will drop and the pressure grew, so that the mixture of air and fuel going into
combustion chamber through a hole flushing.

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