👤 Candidate: Nitish Kumar
📅 Date: [Specify if needed]
🎯 Role: Scientific Officer (Mechanical)
📍 Mode: In-Person
🧭 Focus: Core technical concepts, design logic, and visualization ability
🧱 1. Strength of Materials – Biaxial Stress & Mohr’s Circle
Q1: What is biaxial stress?
Q2: Can pure shear be considered a form of biaxial stress?
➡️ Task: Draw the Mohr’s Circle for pure shear and explain:
- Center
- Radius
- Principal stresses
- Stress transformation at inclined planes
Follow-up:
“How would you find stress on any inclined plane using Mohr’s Circle?”
Explained angle conversion (2θ), graphical interpretation, and application in design.
🛠️ Application-Based Follow-up – Cantilever Beam
Scenario: Cantilever beam with a point load at mid-span
Task:
- Draw deflection curve and bending moment diagram
- Explain design method
- Use bending stress formula: σ=M⋅yI\sigma = \frac{M \cdot y}{I}σ=IM⋅y
Discussion:
- If required diameter d is unavailable, can we use d/2?
- Compared stress levels in both scenarios
- Explained shear stress variation and impact of material selection
- Compared aluminum vs. steel under same loading
Advanced Design Task:
- Combined section with:
- Outer hollow pipe (OD = d, ID = d/2)
- Inner solid rod (d/2)
- Asked to sketch shear stress distribution
- Which failure theory applies?
- Explained Maximum Shear Stress Theory (Tresca)
❗”What if another force is applied at the free end?”
➝ Required modified deflection curve
📐 2. Design & Cross-Section Geometry
Q: Why are circular sections preferred over square or rectangular?
- Higher section modulus for same area
- Better torsional strength
- Efficient stress distribution
Follow-up:
“What if load is applied from opposite ends?”
- Addressed buckling, bending moment, and symmetry
🧮 3. Factor of Safety (FOS) & Thermodynamic Limitations
- Define FOS: FOS=Ultimate stressWorking stress\text{FOS} = \frac{\text{Ultimate stress}}{\text{Working stress}}FOS=Working stressUltimate stress
- Why it’s critical in mechanical design
- Limitations of First Law:
- Doesn’t account for irreversibility, entropy, or quality of energy
🔥 4. Thermodynamics – Piston-Cylinder Analysis
Setup: Horizontal piston-cylinder with unequal P–V conditions on both sides
- Side A: 4P, 4V, T
- Side B: P, V, T
- Ambient: T
Questions:
- What happens when piston is released?
- Is the process adiabatic?
- What are the final pressure, volume, and entropy?
- If one side is vacuum → what happens?
- When gases are suddenly mixed → Prove mathematically that: ΔS>0\Delta S > 0ΔS>0
Task: Plot P–V and H–T diagrams
📌 Solved in Chayan Batch Lecture No. 06
🌡️ 5. Heat Transfer – Multi-Layer Conduction
Scenario: Two slabs in series
- Slab 1: Thermal conductivity = K
- Slab 2: Thermal conductivity = 100K
- ΔT = 300°C to 25°C
Asked:
- Draw temperature profile across slabs
- Why does non-linear drop occur at boundary layer?
- If K → K/2, how does heat flow (Q) change?
- Re-draw updated temperature profile
📌 Covered in Chayan Batch Lecture No. 03
💧 6. Fluid Mechanics – Tank Filling & U-Tube Flow
Q1: Draw Time vs. Height graph for water filling in a tank
Q2: In a reverse U-tube, will drainage happen automatically?
- Sketch Time vs. Height for draining
- Explained siphon effect and hydrostatic pressure difference
📌 Solved in Chayan Batch Lecture No. 09
🧠 Key Takeaways from the Interview
✅ Concept > Formula:
They test your understanding, assumptions, and how well you can defend your answers with logic and visuals—not just formulas.
🖊️ Be Diagram-Ready:
Be prepared to draw:
- Mohr’s Circle
- Deflection Curves
- P–V / H–T Graphs
- Shear Stress Distribution
🔍 Understand Core Principles Deeply:
- Mohr’s Circle and Failure Theories
- Heat flow in layered mediums
- Thermodynamic irreversibility
- Cross-sectional design logic
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