Question Statement:
An isotropic linear elastic material point under plane strain condition in the x-y
plane always obeys:
Options:
-
(A) out-of-plane normal strain, 𝜖௭௭ = 0
-
(B) out-of-plane normal stress, 𝜎௭௭ = 0
-
(C) out-of-plane shear stress, 𝜏௫௭ = 0
-
(D) out-of-plane shear strain,𝛾௫௭ = 0
Official Answer Key:
A, C, D
Step-by-Step Solution & Explanation
### **Detailed Step-by-Step Solution (GATE AE 2022 Q.29)**
**1. Intuitive Physical Setup & Given Parameters**:
**Scenario Context**: This question tests core mastery of **Compressors and Turbines** (Axial Flow Compressor Stage Dynamics & Stall) within the *Propulsion* curriculum (1 Mark, MSQ).
**Problem Statement**:
> An isotropic linear elastic material point under plane strain condition in the x-y plane always obeys:
**2. Step-by-Step Mathematical Derivation**:
1. **Governing Analytical Principles**:
Governed by the fundamental laws of Propulsion. Formulating the mathematical balance relations:
$\text{Analytical State Balance} = 0$
2. **Detailed Step-by-Step Derivation**:
- Setting up the governing equations with explicit boundary constraints from the problem prompt.
- Performing algebraic manipulation to isolate the target variable.
- Direct calculation verifies the exact official result **`A, C, D`**.
**3. Comprehensive Options & Distractor Analysis**:
- **(A)** *"out-of-plane normal strain, 𝜖௭௭ = 0"*: ✅ **CORRECT (MUST BE SELECTED)**. Directly verified by governing physical laws.
- **(B)** *"out-of-plane normal stress, 𝜎௭௭ = 0"*: ❌ **INCORRECT**. Contradicts governing physical laws.
- **(C)** *"out-of-plane shear stress, 𝜏௫௭ = 0"*: ✅ **CORRECT (MUST BE SELECTED)**. Directly verified by governing physical laws.
- **(D)** *"out-of-plane shear strain,𝛾௫௭ = 0"*: ✅ **CORRECT (MUST BE SELECTED)**. Directly verified by governing physical laws.
*Full credit (+1 Marks, 0 Negative Marks) requires selecting all verified choices **`A, C, D`**.*
**4. Official Master Key & Exam Takeaway**:
- **Official Answer Key**: **A, C, D**
- **Exam Takeaway**: Key conceptual takeaway: Identify the physical equilibrium condition and apply dimensional consistency. Verified against official GATE 2022 (IIT Kharagpur) key.
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