All categories

2 years ago

What is hardness and how is it generally tested?

Engineering

1 answer:

drek231 [11]2 years ago

3 0

Answer:

Hardness is understood as the property of materials in general to resist the penetration of an indenter under load, so that the hardness represents the resistance of the material to the plastic deformation located on its surface.

Explanation:

Hardness of a material is understood as the resistance that the material opposes to its permanent surface plastic deformation by scratching or penetration. It is always true that the hardness of a material is inversely proportional to the footprint that remains on its surface when a force is applied.

In this sense, the hardness of a material can also be defined as that property of the surface layer of the material to resist any elastic deformation, plastic or destruction due to the action of local contact forces caused by another body (called indenter or penetrator), harder, of certain shape and dimensions, which does not suffer residual deformations during contact.

That is, hardness is understood as the property of materials in general to resist the penetration of an indenter under load, so that the hardness represents the resistance of the material to the plastic deformation located on its surface.

The following conclusions can be drawn from the previous definition of hardness:

1) hardness, by definition, is a property of the surface layer of the material, and is not a property of the material itself;

2) the methods of hardness by indentation presuppose the presence of contact efforts, and therefore, the hardness can be quantified within a scale;

3) In any case, the indenter or penetrator must not undergo residual deformations during the test of hardness measurement of the body being tested.

To determine the hardness of the materials, durometers with different types of tips and ranges of loads are used on the various materials. Below are the most commonly used tests to determine the hardness of the materials.

Rockwell hardness :

It refers to the Rockwell hardness test, a method with which the hardness or resistance of a material to be penetrated is calculated. It is characterized by being a fast and simple method that can be applied to all types of materials. An optical reader is not required.

Brinell hardness :

Brinell hardness is a scale that is used to determine the hardness of a material through the indentation method, which consists of penetrating with a hardened steel ball tip into the hard material, a load and for a certain time.

This test is not very precise but easy to apply. It is one of the oldest and was proposed in 1900 by Johan August Brinell, a Swedish engineer.

Vickers hardness:

Vickers hardness is a test that is used in all types of solid and thin or soft materials. In this test, a square-shaped pyramid-shaped diamond and a 136° vertex angle are placed on the penetrating equipment.

In this test the hardness measurement is performed by calculating the diagonal penetration lengths.

However, its result is not read directly on the equipment used, therefore, the following formula must be applied to determine the hardness of the material: HV = 1.8544 · F / (dv2).

You might be interested in

The collar A, having a mass of 0.75 kg is attached to a spring having a stiffness of k = 200 N/m . When rod BC rotates about the

gladu [14]

Answer:

Speed=1.633 m/s

Force= 20 N

Explanation:

Ideally, $v^{2}=\frac {ks^{2}}{m}$ hence $v=s\sqrt {\frac {k}{m}}$ where v is the speed of collar, m is the mass of collar, k is spring constant and s is the displacement.

In this case, s=100-0=100mm=0.1m since 1 m is equivalent to 1000mm

k is given as 200 N/m and mass is 0.75 Kg

Substituting the given values

$v=0.1 m\sqrt \frac {200 N/m}{0.75 Kg}=1.632993162 m/s\approx 1.633 m/s$

Therefore, the speed is 1.633 m/s

The sum of vertical forces is given by mg where g is acceleration due to gravity and it's value taken as $9.81 m/s^{2}$

Therefore, $F_y=0.75\times 9.81=7.3575 N\approx 7.36 N$

The sum of forces in normal direction is given by $Ma_n=Ks$ therefore

$Ma_n=200*0.1=20 N$

Therefore, normal force on the rod is 20 N

5 0

3 years ago

Explain the differences between planned and predictive maintenance.

sveticcg [70]

Answer:

Planned maintenance refers to any scheduled activity carried out to check a machine is working ok and diagnose procedures to fix it if need it. On the other hand, predictive mainteance is all the techniques which help to define if a machine requires or not maintenance activities so far.

Explanation:

Planned maintenance is based on preventive routines to ensure a machine is working in acceptable conditions and at the same time prevent them to change to risky values performing acticities like parts replacement, cleaning, etc. The key of this maintenance is schedule, that is to say, is a maintenance that has to be carried out constantly each certain time. Predictive maintenance is different because it is used to define if a machie needs any kind of inspection or if, on the contrary, the machine can continue operating without any intervention. The good point about predictive maintenance is the capability of telling when a maintenance is required and when is no necessarily required which is ideal to save costs.

7 0

3 years ago

A well-insulated tank in a vapor power plant operates at steady state. Saturated liquid water enters at inlet 1 at a rate of 125

kompoz [17]

Answer:

a. The mass flow rate (in lbm/s) is 135lbm/s

b. The temperature (in o F) is 200.8°F

Explanation:

We assume that potential energy and kinetic energy are negligible and the control volume operates at a steady state.

Given

a. The mass flow rate (in lbm/s) is 135lbm/s

m1 = Rate at inlet 1 = 125lbm/s

m2 = Rate at inlet 2 = 10lbm/s

The mass flow rate (in lbm/s) is calculated as m1 + m2

Mass flow rate = 125lbm/s + 10lbm/s

Mass flow rate = 135lbm/s

Hence, the mass flow rate (in lbm/s) is 135lbm/s

b. To calculate the temperature.

First we need to determine the enthalpy h1 at 14.7psia

Using table A-3E (thermodynamics)

h1 = 180.15 Btu/Ibm

h2 at 14.7psia and 60°F = 28.08 Btu/Ibm

Calculating h3 using the following formula

h3 = (h1m1 + h2m2) / M3

h3 = (180.15 * 125 + 28.08 * 10)/135

h3 = 168.8855555555555

h3 = 168.89 Btu/Ibm

To get the final temperature; we make use of table A-2E of thermodynamics.

Because h3 < h1, it means the liquid is at a compressed state.

The corresponding temperature at h3 = 168.89 is 200.8°F

The temperature (in o F) is 200.8°F

6 0

3 years ago

A cubic transmission casing whose side length is 25cm receives an input from the engine at a rate of 350 hp. If the vehicle's ve

Musya8 [376]

Answer:

The surface temperature is 921.95°C .

Explanation:

Given:

a=25 cm ,P=350 hp⇒P=260750 W

Power transmitted $0.95\times 260750$ W and remaining will lost in the form of heat.This heat transmitted to air by the convection.

h=230 $\frac{W}{m^2-K},\eta =0.95$

Actually heat will be transmit by the convection.

In convection Q=hA $\Delta T$

So $P=\Delta T\times Q$

$0.05\times 260750=230\times0.25^2\(T-15)$

T=921.95°C

So the surface temperature is 921.95°C .

6 0

3 years ago

A bus travels the 100 miles between A and B at 50 mi/h and then another 100 miles between B and C at 70 mi/h.

stira [4]

Answer:

c. less than 60 mi/h

Explanation:

To calculate the average speed of the bus, we need to calculate the total distance traveled by the bus, as well as the total time of travel of the bus.

Total Distance Traveled = S = 100 mi + 100 mi

S = 200 mi

Now, for total time, we calculate the times for both speeds from A to b and then B to C, separately and add them.

Total Time = t = Time from A to B + Time from B to C

t = (100 mi)/(50 mi/h) + (100 mi)(70 mi/h)

t = 2 h + 1.43 h

t = 3.43 h

Now, the average speed of bus will be given as:

Average Speed = V = S/t

V = 200 mi/3.43 h

V = 58.33 mi/h

It is clear from this answer that the correct option is:

c. less than 60 mi/h

7 0

3 years ago