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All questions of Principal Stresses & Strains (Mohr`s Circle) for Mechanical Engineering Exam

Which point on the stress strain curve occurs after yield plateau?
  • a)
    Ultimate point
  • b)
    lower yield point
  • c)
    Upper yield point
  • d)
    Breaking point
Correct answer is option 'A'. Can you explain this answer?

Jaya Yadav answered
Ultimate Point on the Stress-Strain Curve:
The ultimate point on the stress-strain curve is the point that occurs after the yield plateau. This point represents the maximum stress that a material can withstand before it fails or fractures. It is also known as the ultimate tensile strength (UTS) or simply the breaking point.

Explanation:
The stress-strain curve is a graphical representation of the relationship between the applied stress and the resulting strain in a material. It provides valuable information about the mechanical properties and behavior of the material under different loading conditions.

Yield Plateau:
The yield plateau is the region on the stress-strain curve where the material undergoes plastic deformation without experiencing a significant increase in stress. It indicates the onset of yield, which is the point where the material starts to undergo permanent deformation.

Lower Yield Point:
The lower yield point is the first drop in stress that occurs after the elastic region on the stress-strain curve. It represents the point where the material transitions from elastic to plastic deformation. However, this point is not relevant to this question as it occurs before the yield plateau.

Upper Yield Point:
The upper yield point is the highest stress value reached on the stress-strain curve before the yield plateau. It is typically observed in certain materials, such as low-carbon steel, and represents a temporary softening of the material due to localized necking. However, this point is also not relevant to this question as it occurs before the yield plateau.

Breaking Point:
The breaking point or fracture point is the point on the stress-strain curve where the material fails and fractures. It occurs after the ultimate point and represents the maximum stress that the material can withstand before complete failure.

Conclusion:
In summary, the ultimate point on the stress-strain curve occurs after the yield plateau. It represents the maximum stress that a material can withstand before it fails or fractures. The lower yield point, upper yield point, and breaking point are all distinct points on the stress-strain curve, but they occur either before or after the yield plateau. Therefore, the correct answer to the question is option 'A' - Ultimate point.

Complimentary shear stresses are
  • a)
    equal both in magnitude and sign
  • b)
    equal in magnitude but opposite in sign
  • c)
    unequal in magnitude but of same sign
  • d)
    equal in magnitude, and the direction may be same or opposite
Correct answer is option 'B'. Can you explain this answer?

Kajal Tiwari answered
**Complimentary Shear Stresses:**

Complimentary shear stresses refer to shear stresses acting on two mutually perpendicular planes in a solid material. These shear stresses are equal in magnitude but opposite in sign.

**Explanation:**

When a solid material is subjected to shear stress, it deforms and experiences internal forces. These internal forces can be resolved into normal stresses and shear stresses acting on different planes within the material.

When considering shear stresses on two mutually perpendicular planes, they are called complimentary shear stresses. The magnitudes of these shear stresses are equal, but their signs are opposite.

**Example:**

Let's consider a simple example to understand this concept. Suppose a rectangular block is subjected to shear stress along the x-axis. The shear stress acting on the xz-plane will be positive, indicating a shear force in the positive x-direction. Simultaneously, the shear stress acting on the yz-plane will be negative, indicating a shear force in the negative x-direction.

This means that the shear stress acting on the xz-plane and the shear stress acting on the yz-plane are equal in magnitude but opposite in sign. They are complimentary shear stresses.

**Importance:**

Complimentary shear stresses are essential in understanding the distribution of internal forces within a material. They help in analyzing the deformation and failure of structural components when subjected to shear stress. By considering the complimentary shear stresses, engineers can design structures that can withstand these forces without failure.

In conclusion, complimentary shear stresses are equal in magnitude but opposite in sign. They play a significant role in understanding the behavior of materials under shear stress and are essential in engineering design and analysis.

The shear stress along the principal plane subjected to maximum principal stress is
  • a)
    minimum
  • b)
    maximum
  • c)
    zero
  • d)
    any value depending on loading
Correct answer is option 'C'. Can you explain this answer?

The shear stress along the principal plane subjected to the maximum principal stress is zero.

Explanation:
- When a material is subjected to external forces, it experiences stresses in different directions. These stresses can be decomposed into normal and shear stresses.
- The principal stresses are the maximum and minimum normal stresses experienced by a material at a particular point.
- The principal planes are the planes on which the principal stresses act. These planes are perpendicular to each other.
- The maximum principal stress is the highest normal stress experienced by the material, and it occurs on the principal plane with the highest normal stress value.
- The minimum principal stress is the lowest normal stress experienced by the material, and it occurs on the principal plane with the lowest normal stress value.
- Shear stress occurs when forces are applied parallel to a plane, causing one part of the material to slide over the adjacent part. It is perpendicular to the normal stress.
- Along the principal planes, the shear stress is zero. This is because the principal planes are oriented in such a way that the maximum and minimum normal stresses act purely in the normal direction and do not cause any shearing motion.
- The shear stress can be calculated using the formula: shear stress = (maximum principal stress - minimum principal stress) / 2. Since the minimum principal stress is zero on the principal plane subjected to the maximum principal stress, the shear stress is also zero.

In conclusion, the shear stress along the principal plane subjected to the maximum principal stress is zero.

On an aluminium sample, strain readings were recorded on 3-element delta rosette as follows. ε = −100 μs, ε120° = −500 μs and ε60° = +600 μs Then the maximum tensile strain is __________ μs.
(A) 589
(B) 600
    Correct answer is option ''. Can you explain this answer?

    Lavanya Menon answered
    Ε0 = εxx = −100 μs ⋯ ①
    ε120° = −500 μs =
    −500 = −25 + 0.75 εyy − 0.433 γxy
    or − 475 = 0.75 εxy − 0.433 γxy ⋯ ②
    ε60° = 600 =
    = 25 + 0.75 εyy + 0.433 γxy
    575 = 0.75 εyy + 0.433 γxy ⋯③
    −475 = 0.75 εyy − 0.433 γxy ⋯④
    100 = 1.5 εyy
    or εyy = +66.67 μs
    Putting the values in equation ③
    575 = 0.75 × 66.67 + 0.433 γxy = 50 + 0.433 γxy
    γxy = 1212.5 μs
    Now = −16.665 μs
    = −83.33 μs
    =
    = √(−83.33)2 + (606.25)2
    √6943.9 + 367539 = 611.95 μs
    Principal strains εp1 = −16.665 + 611.95 = +595.285 μs
    εp2 = −16.665 − 611.95 = −628.615 μs
    Question_Type: 5

    The value of σ at failure according to strain energy theory
    • a)
      100 MPa
    • b)
      75 MPa
    • c)
      90 MPa
    • d)
      150 MPa
    Correct answer is option 'C'. Can you explain this answer?

    Zoya Sharma answered
    According to strain energy theory
    σ12 + σ22 + σ32 − 2μ(σ1σ2 + σ2σ3 + σ3σ1) ≤
    4.95 σ2 = (200)2
    σ = 89.89 MPa ≈ 90 MPa

    At the principal planes
    • a)
      the normal stress is maximum or minimum and the shear stress is zero
    • b)
      the tensile and compressive stresses are zero
    • c)
      the tensile stress is zero and the shear stress is maximum
    • d)
      no stress acts
    Correct answer is option 'A'. Can you explain this answer?

    Janhavi Datta answered
    Principal stresses are maximum or minimum normal stresses which may occur on a stressed body. In a 3-D body there may three principal planes which are mutually perpendicular to each other. The plane of principle stresses is called principal plane which always carries zero shear stress.

    Biaxial stress system is correctly shown in
    • a)
    • b)
    • c)
    • d)
    Correct answer is option 'D'. Can you explain this answer?

    Sarita Yadav answered
    Complementary shear stresses are balanced Normal stress is balanced in x and y-direction.

    If Normal stresses of same nature px and py and shear stress q is acting on two perpendicular planes and q = (pxpy)1/2, then the major and minor principal stresses respectively are
    • a)
      px + py and px − py
    • b)
      px and px − py
    • c)
      0.5 (px + py)and 0.5 (px − py )
    • d)
      px + py and zero
    Correct answer is option 'D'. Can you explain this answer?

    Meera Bose answered
    Major and Minor Principal Stresses

    The given question is asking for the major and minor principal stresses when normal stresses of the same nature (px and py) and a shear stress (q) are acting on two perpendicular planes. The relationship between these stresses is given as q = sqrt(px * py).

    To determine the major and minor principal stresses, we need to understand the concept of principal stresses and how they relate to the given normal and shear stresses.

    Principal stresses are the maximum and minimum values of normal stresses that act on a particular point in a material. They are represented by sigma1 (major principal stress) and sigma2 (minor principal stress).

    To find the major and minor principal stresses, we can use the following equations:

    sigma1 = (px + py)/2 + sqrt(((px-py)/2)^2 + q^2)
    sigma2 = (px + py)/2 - sqrt(((px-py)/2)^2 + q^2)

    Now, let's solve the given problem step by step:

    Step 1: Given normal stresses:
    px and py are normal stresses acting on two perpendicular planes.

    Step 2: Shear stress:
    q = sqrt(px * py)

    Step 3: Major Principal Stress (sigma1):
    sigma1 = (px + py)/2 + sqrt(((px-py)/2)^2 + q^2)
    = (px + py)/2 + sqrt((px^2 - 2pxpy + py^2)/4 + pxpy)
    = (px + py)/2 + sqrt((px^2 + 2pxpy + py^2)/4)
    = (px + py)/2 + sqrt((px + py)^2)/2
    = (px + py)/2 + (px + py)/2
    = px + py

    Therefore, the major principal stress (sigma1) is equal to px + py.

    Step 4: Minor Principal Stress (sigma2):
    sigma2 = (px + py)/2 - sqrt(((px-py)/2)^2 + q^2)
    = (px + py)/2 - sqrt((px^2 - 2pxpy + py^2)/4 + pxpy)
    = (px + py)/2 - sqrt((px^2 + 2pxpy + py^2)/4)
    = (px + py)/2 - sqrt((px + py)^2)/2
    = (px + py)/2 - (px + py)/2
    = 0

    Therefore, the minor principal stress (sigma2) is equal to zero.

    Hence, the major and minor principal stresses are px + py and zero respectively, which corresponds to option D.

    A circle of diameter 500 mm is inscribed on a square plate of copper, before the application of stresses as shown, σ1 = 160 MPa, σ2 = 80 MPa, τ = 30 MPa. After the application of stresses, the circle is deformed into an ellipse. Then the major and minor axes of the ellipse will be Given E = 100 GPa, ν = 0.35.
    • a)
      Major = 500.73 mm, Minor = 500.05 mm
    • b)
      Major = 480.61 mm, Minor = 420.21 mm
    • c)
      Major = 250.13 mm, Minor = 230.31 mm
    • d)
      Major = 460.51 mm, Minor = 448.31 mm
    Correct answer is option 'A'. Can you explain this answer?

    = 120 MPa
    = 40 MPa
    where τ = 30 MPa
    = √402 + 302 = 50 MPa
    Principal stresses, p1 = 120 + 50 = 170 MPa p2 = 120 − 50 = 70 MPa
    Principal strains,
    e1 =
    =
    = 1455 × 10−6 = 1455 μ strain
    e2 =
    = 105 × 10−6 = 105 μ strain
    Major axis = 500 + 1455 × 10−6 × 500
    = 500 + 0.7275 = 500.7275 mm
    Minor axis = 500 + 105 × 10−6 × 500
    = 500 + 0.0525 = 500.0525 mm
    Principal angles, θ1 =
    =
    θ1 = −18.44 ° as shear stress on reference plane is positive

    The value of σ at failure according to maximum principal stress theory
    • a)
      100 MPa
    • b)
      250 MPa
    • c)
      150 MPa
    • d)
      50 MPa
    Correct answer is option 'A'. Can you explain this answer?

    Athul Kumar answered
    Understanding Principal Stresses
    The problem involves calculating shearing and normal stresses based on given principal stresses. The principal stresses are 250 MPa (tensile) and 150 MPa (compressive).
    Stress Components on a Plane
    1. Normal Stress (σ₁):
    - Given as 200 MPa (tensile).
    2. Finding Normal Stress on the Orthogonal Plane:
    - The orthogonal plane will experience a different normal stress, denoted as σ₂.
    - To find σ₂, we can utilize the relationship between normal and shear stresses.
    Calculating Shear Stress
    1. Using the Mohr's Circle Concept:
    - The maximum shear stress (τ_max) is calculated using the formula:
    τ_max = (σ₁ - σ₂) / 2.
    2. Applying the Principal Stresses:
    - With σ₁ = 250 MPa (tensile) and σ₂ = -150 MPa (compressive), we find:
    - The stress on the plane at 200 MPa tensile (σ₁ = 200) implies we need to calculate the orthogonal stress:
    - σ₂ = 50 MPa (compressive).
    Final Results
    1. Shearing Stress Calculation:
    - τ = (200 - 50) / 2 = 75 MPa (shear).
    2. Normal Stress on the Orthogonal Plane:
    - The normal stress is σ₂ = 100 MPa (compressive).
    3. Conclusion:
    - The shearing stress is 50√7 MPa, and the normal stress on the orthogonal plane is 100 MPa (compressive).
    Thus, the correct answer is option 'C': 50√7 MPa and 100 MPa (compressive).

    Following stress Tensor represents tri-axial state of stress at a point. Determine the distortion energy per unit volume in terms of kJ/m3 . Take μ = 0.3, E = 200 GPa
    [σ] =
    (A) 1.682
    (B) 1.682
      Correct answer is option ''. Can you explain this answer?

      Given,
      σx = 10 MPa
      σy = 20 MPa
      σz = −10 MPa
      τxy = 5 MPa
      τxz = τyz = 0
      σ1,2 =
      =
      = 15 ± √52 + 52
      σ1 = 22.07 MPa
      σ2 = 3.82 MPa
      σ3 = σ2 = −10 MPa [∵ τyz = τxz = 0]
      Distortion energy per unit volume
      =
      = + +(3.82 + 10)2 + (−10 − 22.07)2]
      = 1.682 × 10−3 mJ/m3
      = 1.682 kJ/m3
      Question_Type: 5

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