Structures and Properties of Materials Quiz

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Questions and Answers

What is the definition of stress in the context of material deformation?

The amount of force applied over a unit area (correct)

The measure of deformation per unit length

The ratio of change in length to original length

The total force acting on a material

Which of the following statements accurately describes plastic deformation?

It allows a material to return to its original shape

It results in a permanent change in shape (correct)

It occurs only when a material is unloaded

It is temporary and reversible

What does Young's modulus measure?

The maximum stress a material can withstand

The ratio of stress to strain within the elastic limit (correct)

The total deformation of a material

The total energy absorbed by a material

According to Hooke’s law, how is stress related to strain?

They are directly proportional within the elastic limit Signup and view all the answers

Which type of load involves pushing or crushing a workpiece?

Compression Signup and view all the answers

What characterizes elastic deformation?

It is fully recoverable when the load is removed Signup and view all the answers

In a stress-strain curve, what region corresponds to elastic behavior?

Elastic limit Signup and view all the answers

What happens to materials that exceed their elastic limit?

They can no longer return to their original shape Signup and view all the answers

What is the primary function of a load cell?

To convert applied force into digital values Signup and view all the answers

How does a strain gauge load cell measure force?

By changing its voltage output directly proportional to the load Signup and view all the answers

What is required to calibrate a testing machine using a load cell?

Substituting the load cell for the specimen in the machine Signup and view all the answers

What is the major difference between analog and digital signals?

Analog signals have continuous electrical signals while digital signals are non-continuous Signup and view all the answers

When should a testing machine be calibrated?

Regularly, regardless of performance Signup and view all the answers

What is a data acquisition system primarily used for?

Measuring or controlling physical characteristics Signup and view all the answers

What happens to the body of a load cell when a load is applied?

It deforms slightly Signup and view all the answers

What is the primary function of an LVDT?

To measure small movements or deformations Signup and view all the answers

Which statement correctly describes the basic principle of LVDT operation?

It is based on mutual induction between coils Signup and view all the answers

What can be said about the sensitivity range of commercial LVDTs?

Their sensitivity range varies from 0.003 to 0.25 V/mm Signup and view all the answers

What component is essential in a strain gauge for measuring changes in resistance?

A Wheatstone bridge circuit Signup and view all the answers

What happens to the resistance of a strain gauge as it is strained?

It increases proportionally Signup and view all the answers

What is the typical gauge length range for strain gauges?

5 mm to 15 mm Signup and view all the answers

What type of energy conversion occurs in an LVDT?

Mechanical to electrical Signup and view all the answers

Which statement best describes the relationship between core position and output voltage in an LVDT?

They are directly proportional Signup and view all the answers

What materials commonly make up the element of a strain gauge?

Foil or wire on plastic or paper base Signup and view all the answers

What is the purpose of the adhesive in a strain gauge?

To bond the strain gauge to the surface under measurement Signup and view all the answers

What happens to the electric resistance of a strain gauge when the length of the gauge increases due to applied load?

It increases linearly. Signup and view all the answers

What does the gauge factor (GF) of a strain gauge represent?

The ratio of the fractional change in resistance to strain. Signup and view all the answers

Which of the following is NOT an advantage of a mechanical dial gauge compared to an electrical strain gauge?

It is smaller in size. Signup and view all the answers

In what way can an electrical strain gauge be affected during measurements?

By temperature and humidity. Signup and view all the answers

Which characteristic differentiates an electrical strain gauge from a mechanical dial gauge?

Ability to read dynamic loads. Signup and view all the answers

Which statement about dial gauges is true?

They have limited magnification for deformation. Signup and view all the answers

What occurs when a strain gauge is deformed?

The electric resistance increases. Signup and view all the answers

Which of the following is a disadvantage of an electrical strain gauge?

High cost and need for supplementary components. Signup and view all the answers

In the equation $R=\rho \frac{L}{A}$, what do the symbols represent?

$R$ is resistance, $\rho$ is resistivity, $L$ is length, $A$ is area. Signup and view all the answers

What is the main purpose of laboratory testing devices?

To determine the load-displacement relationship Signup and view all the answers

Which device is specifically designed to apply load and measure it accurately during tests?

Testing Machine Signup and view all the answers

What kind of measurements can the dial gauge perform?

Small linear displacements Signup and view all the answers

What mechanical principle does a dial gauge operate on?

Gears and spindle movement Signup and view all the answers

Which of the following is NOT a function of an extensometer?

Assessing temperature effects Signup and view all the answers

Which component is NOT part of a dial gauge?

Load Cell Signup and view all the answers

Which type of testing machinery can be used for bending tests?

Bending Testing Machine Signup and view all the answers

How does a dial gauge convert linear movement into a measurement output?

By mechanically magnifying movement with gears Signup and view all the answers

What is the primary application of strain gauges?

Detecting a change in resistance due to deformation Signup and view all the answers

In a laboratory setting, what role does a data acquisition system play?

To collect and interpret measurement data Signup and view all the answers

Study Notes

Course Information

Course Title: Structures and Properties of Materials
Course Code: MCE132
Instructor: Dr. Shady Abdelnasser, PhD
Department: Energy and Renewable Energy Engineering
University: Egyptian Chinese University

Stress-Strain Curve & Measuring Devices

Deformation is the action or process of changing shape
Applying force to a sample can cause compression, stretching or bending
Stress is the amount of force exerted per unit area (σ = F/A)
Strain is the amount of stretching or compressing that occurs due to stress (ɛ = (Lfinal - Linitial)/Linitial = ΔL/L)
Materials react to stress differently

Types of Loads

Compressing
Stretching
Bending

Elastic and Plastic Deformation

Elastic deformation is recoverable
Plastic deformation is permanent
Elastic deformation occurs within the elastic limit of a material
The ratio of stress and strain remains constant in the elastic region. This is known as Hooke's Law
Stress is directly proportional to strain

Laboratory Testing Devices

Testing Machines: Used to apply loads and measure them accurately. Different types exist (tension, compression, bending)
Dial Gauges: Mechanical devices measuring small linear displacements or variations in a workpiece. Attached to two points, the gauge measures the relative movement between them. Accuracy can be up to 0.001mm. The upward pressure on the spindle/plunger is transferred to the gears and indicated on the dial using a pointer.
LVDT (Linear Variable Differential Transformer): An electrical device. It converts linear motion into an electrical signal. Used to measure small movements or deformations. Sensitivity of commercial LVDTs ranges from 0.003 to 0.25 V/mm. Its operation is based on mutual induction. A metallic part moving in a magnetic field creates an output voltage related to the magnitude of the movement.
Strain Gauges: Electrical devices for measuring small deformations (strain) within a specific gauge length (typically 5-15 mm). The gauge's electrical resistance changes proportionally to the strain. Bonded to surfaces, they deform with the surface, and the resistance change is measured using a Wheatstone bridge.
Load Cells: A force-measuring device. It converts an applied force to a digital value. They are equipped with strain gauges affixed to the body of the load cell.

Data Acquisition System

Data acquisition involves collecting, processing, and storing data from different source systems.
A data acquisition system uses software and hardware to measure and control physical characteristics of real-world objects.

Signal Conditioning

Analog and digital signals carry information.
Analog signals have continuous electrical signals, while digital signals have non-continuous signals.

Calibration

Calibration ensures the readings accurately reflect the applied load.
Calibration methods include placing the load cell in the tested machine's specimen position.
Regular, timely calibration is critical for accurate measurements, and calibrating after manufacturing as well as when equipment moves, are important.
Percent error can be calculated by [ (Machine Reading - True load) / True load ] x 100

Definitions

Accuracy: Degree of correctness in measurement readings.
Sensitivity: Minimum measurable value.
Capacity: Maximum measurable value.
Range: Difference between maximum and minimum measurable values.
Precision: Consistency in repeated measurements of the same value.

Materials Science and Engineering Fundamentals

Study of materials; compositions, structures, synthesis, and processing
Materials properties affect selection, and thus projects, economically
Engineers must understand materials properties for appropriate choices

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Description

Test your understanding of the stress-strain curve and the concept of deformation. This quiz covers types of loads, elastic and plastic deformation, and how materials react under different stresses. Perfect for students of MCE132.