materials science test 1 conceptual questions

What is Engineering Stress?

Force acting per unit area over which the force is applied S=F/Ao

What is Engineering Strain?

Change in dimension per unit lengthe=(L-Lo)/Lo

What is True Stress?

Force acting per unit area over the current cross sectional area

What is True Strain?

Strain that accounts for continuously changing length using a natural log function

What is the relationships of engineering stress and True stress?

True stress is the instantaneous applied force divided by the material's current (actual) cross-sectional area during deformation. engineering stress is the force over the initial area.

What is the relationships of engineering strain and True strain?

True strain is the natural logarithm of one plus engineering strain, accounting for continuous changes in length during deformation.

What is Young's Modulus?

The slope of a tensile stress-straincurve in the linear regimeE=S/e

What is elastic deformation?

deformation that occurs within the elastic region. the material can return to its original shape with the release of applied stress

What is plastic deformation?

deformation that occurs outside of the elastic region from applied stress causing permanent deformation

What is Yield Strength?

The magnitude of stress at which plastic deformation commences

What is Ultimate Tensile Strength?

the maximum stress that a material can withstand before necking occurs

What is Fracture Tensile Strength?

Fracture tensile strength is the stress at which a material actually breaks or fractures during a tensile test. occurs after UTS and necking

what is poisson's ratio?

The negative of the ratio between the lateral and longitudinal strains in the elastic region. ν = - e lateral / e longitudinal

What is tensile toughness?

Energy absorbed by a material prior to fracture. the summation of area in the stress-strain curve

What is the failure criteria of tensile failure?

Tensile failure occurs when the applied stress in a material exceeds its tensile strength, causing permanent deformation or fracture.

What is the failure criteria of shear failure?

Shear failure occurs when the applied shear stress on a material exceeds its shear strength, causing the material to slide or deform along a plane.

Which tests could not be used to test brittle materials?

Brittle materials cannot be reliably tested using tests that require significant plastic deformation, because they fracture before yielding.

-Tensile tests measuring yield strength

-Impact tests that rely on ductility (charpy)

-Bend/flexural tests with LARGE deflection. small deflection in a bend test is allowable

What quantity usually is used to measure ductility of materials?

percent elongation

What kind of indenter and load are used for Rockwell C test?

1/8th or 1/16th steel ball for soft materials, Diamond cone or brale for hard materials. 150KG load

What kind of indenter and load are used for Rockwell B test?

Hardened steel ball with a 150KG load

What is Shear Modulus?

Slope of the linear part of the shearstress-shear strain curve.

G= Tau/Gamma

What is Shear thickening?

Materials in which the apparent viscosity increases with increasing rate of shear

What is Shear thinning?

Materials in which the apparent viscosity decreases with increasing rate of shear

What is Impact Loading?

When materials are subjected to high strain rates, we refer to this type of loading as impact loading.

What is impact toughness?

Ability of a material to withstand an impact blow

What is strain rate?

Strain rate (s-1 ) is the rate at which strain develops in a material

How strain rate affects the behavior of materials?

materials that experience a sudden increase in strain rate appear to be stronger but more brittle

What kind of materials can be tested with tensile test?

ductile, non-brittle materials that can withstand some deformation to produce a curve

What kind of materials cannot be tested with tensile tests?

Brittle materials that will fracture before producing a deformation curve

Which test could be used to test brittle materials?

Bend test, charpy test, compression test, hardness test

What is the relationships of tensile strength and hardness?

Tensile strength typically increases with material hardness

What will affect the properties of materials?

Material properties are determined by composition, microstructure, processing history, and service conditions.

What will affect the result of a Charpy test?

Charpy impact test results are affected by temperature, strain rate, specimen geometry, and material microstructure

What is transition temperature?

the temperature at which a material changes from ductile to brittle

what is fracture mechanics?

a discipline in materials science which concerns the presence of small cracks or imperfections within studied materials

What is the basic modes of Fracture Mechanics?

1. opening

2. in-plane shear

3. out of plane shear

Which quantity is used to evaluate the fracture (fracture propagation)?

Fracture toughness is the quantity used to evaluate a material's resistance to crack propagation. Kic

How to determine the stress concentration at a crack tip?

The stress concentration at a crack tip is determined using the stress intensity factor, K

What is failure criteria of fracture?

Fracture occurs when the stress intensity factor at a crack tip reaches or exceeds the material's fracture toughness. K>Kic

What will affect fracture behavior of a sample?

Fracture behavior is affected by material properties, crack characteristics, temperature, loading conditions, and environment.

What is fracture toughness?

Fracture toughness is a material property that measures a material's resistance to crack propagation. Kic

What will affect the fracture of materials?

Fracture of a material is affected by its microstructure, defects, stress, temperature, loading rate, and environment.

What is ductile fracture? What is the characteristic of the ductile fracture?

Ductile fracture occurs through the grains.

considerable amount of deformation before fracture.

begins with nucleation, goes to growth, and finishes with coalesence.

what is brittle fracture? what is the characteristic of brittle fracture?

little to no plastic deformation. occurs in high strength metals with poor ductility and toughness.

What is Fatigue?

lowering or strength or failure within a material caused by repetitive applied stress.

What is Endurance limit of material?

The limit at which an applied stress on a material undergoing cyclical loading will face fatigue failure at a certain point. below the stress of endurance limit, the material can go for an unlimited amount of cycles (10^7~~~)

Which material does not have Endurance limit?

Aluminum

what is cold working?

a process in which a material is deformed to increase its strength via material properties

What is strain hardening?

a process in which a ductile material has its strength properties increased through deformation. strain hardening techniques result in the material becoming more brittle.

What is the relationship of plastic deformation and strength of materials?

As a material undergoes plastic deformation, its strength increases due to strain hardening, but its ductility decreases.

What is the relationship of plastic deformation and ductility?

As a material undergoes plastic deformation its ductility decreased and it becomes more brittle.

What is measurement of cold working?

percentage of area reduction during the manufacturing process

What are the Characteristics of Cold Working?

the tensile and yield strength increase with a decrease in % elongation meaning the material becomes more brittle with more cold working done

What are the advantage of cold working?

Cold working increases strength and hardness of a material without the need for heat, while improving surface finish and dimensional accuracy.

What are the undesirable effects of cold working?

The worked material loses ductility and creates residual stress