impact test on steel sample

8. To perform impact test on Steel Sample[17-12-2008]

Objective To determine modulus of toughness in bending and in tension.

ApparatusCharpy’s Impact Testing Machine, Steel Specimen (Rectangular for bending, Circular for tension)

Related Theory

ToughnessThe ability if a material to absorb energy within plastic zone is called toughness.

Modulus of toughness (MOT)Energy absorbed per unit volume as the specimen is loaded from zero to failure point.

MOT=∆ EV

= J

mm3=Nmmmm3

=MPa

Types of Load

Static LoadA load which does not change its position, magnitude and direction is termed as static load. For example self weight of any body.

Dynamic LoadA load which changes its position, magnitude and direction is termed as static load. For example load in elevators, cranes etc.

Impact LoadSudden application of a large magnitude of load for a very short period of time is termed as impact load. For example Landing of Aero planes, impact of moving vehicle on expansion joints, movement of railways, removal of framework.

1 Impact Test 07Civil73

Derivation

MOT=∆ EV

Energy transferred to sample = ΔE = E1-E2

∆ E=mgh1−mgh2=mg (h1−h2 )………… (1 )

h1=h0+R sin(θ1−90 °)

h1=h0+R cosθ1

Similarly

h2=h0−R cosθ2

Putting h1 and h2 values in eq. (1)

∆ E=mg ((h0+R cosθ1 )− (h0−R cos θ2 ))

∆ E=mgR (cosθ2−cosθ1 )

Hence proved , MOT=∆ EV

So by potting the value of ΔE, we can find MOT.

Note: This derivation is limited to this machine only.


Procedure

For Bending First of all measure the θ1without placing the rectangular steel specimen in the machine.

Now Place the rectangular specimen and measure the value ofθ2. It is to be noted that θ1will be

greater than θ2 .

For Tension Fix the tension producing assembly with the head of machine. Measure θ1without the circular steel rod.

Measure θ2 without by attaching circular rod in the assemblyFinally calculate the value of MOT for both the cases.

Steel Samples after Fracture


Steel Sample for Bending

Steel Sample for Tension

Calculations and Observations

Mass of Fork = 22.9 kg g= 9.81 m/sec2 = 9810 mm/ sec2

Radius of Fork =R= 0.7m = 700mm Volume of specimen (For bending) = 0.335 in3 = 5489.66mm3

Volume of specimen (For tension) = 0.25 in3 = 4096.76mm3

Specification Height Attained by Fork ΔE Volume MOTFinal (θ2) ΔE/Vol

degrees degreesBending 142 130 22.8369 5489.66 4.159

Tension 144 107 81.242 4096.75 19.831

Initial (θ1)mm3

X106

X106

Comments

In bending case a groove was made in the specimen, this is because we know that this will fail in shear, so to facilitate this process and to ensure the shear failure, we provide a groove in specimen.

And so for the same reasons we provided all round rings or a thread in circular steel rod specimen.

In bending test the specimen failed producing unsharp edges; this is because it was not brittle. In our case, rectangular steel bar used for bending test is more ductile, because in didn’t get

fully fracture.


impact test on steel sample

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