Top 50+ Strength of Materials Interview Questions and Answers

Ace your Strength of Materials (SOM) interviews with this detailed guide of 50+ important questions and answers. Ideal for mechanical, civil, and structural engineering roles.

Shivani Dhondiyal 1 day agoLast Updated: May 27, 2025

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Top 50+ Strength of Materials Interview Questions and Answers

Are you preparing for an interview in Mechanical, Civil, or Structural Engineering? One of the most commonly tested subjects is Strength of Materials (SOM) a core pillar of engineering design and analysis.

Strength of Materials is the branch of mechanics that deals with the behavior of solid objects under various types of loads and conditions. From bridges and beams to shafts and columns, SOM principles are critical for designing safe and efficient structures.

This guide is designed to help both freshers and experienced candidates crack SOM interviews confidently. We’ve compiled a list of 50+ important SOM interview questions, covering fundamental concepts, stress-strain relationships, bending, torsion, and real-world applications.

Bookmark this page and share it with your friends it’s a must-have for any serious interview preparation!

Basic SOM Interview Questions and Answers

Q1. What is Strength of Materials?

Answer:
Strength of Materials is the study of how different materials behave under various types of loading. It involves analyzing the ability of a material to resist deformation and failure when subjected to forces like tension, compression, shear, and torsion.

Q2. What is the difference between Stress and Strain?

Answer:

Stress (σ): Internal resistance offered by the material per unit area.
$Pascal)\sigma = \frac{\text{Force}}{\text{Area}} \quad (\text{N/m² or Pascal})$
Strain (ε): Deformation per unit length caused due to applied stress.
$length(dimensionless)\varepsilon = \frac {\text {Change in length}}{\text{Original length}} \quad (\text{dimensionless})$

Q3. State Hooke’s Law.

Answer:
Hooke’s Law states that within elastic limit, stress is directly proportional to strain:

$σ∝ε⇒σ=Eε\sigma \propto \varepsilon \quad \Rightarrow \quad \sigma = E\varepsilon$

Where E is the Young’s modulus or modulus of elasticity.

Q4. What is Young’s Modulus?

Answer:
Young’s Modulus (E) is the ratio of normal stress to longitudinal strain. It represents the stiffness of a material.

$\frac{\sigma}{\varepsilon}$

Higher E means a stiffer material.

Q5. What is Poisson’s Ratio?

Answer:
It is the ratio of lateral strain to longitudinal strain when a material is stretched or compressed.

$strain\text{Poisson’s Ratio} (\nu) = -\frac{\text{Lateral strain}}{\text{Longitudinal strain}}$

For most metals, Poisson’s ratio lies between 0.25 to 0.35.

Q6. Define Elasticity and Plasticity.

Answer:

Elasticity: Property of a material to return to its original shape after the removal of load.
Plasticity: Property that allows permanent deformation after exceeding the elastic limit.

Q7. What is the difference between Ductile and Brittle materials?

Answer:

Property	Ductile Material	Brittle Material
Deformation	Large (plastic)	Very little (fracture)
Example	Steel, Copper	Glass, Cast Iron
Behavior	Absorbs energy before break	Breaks suddenly

Q8. What is the Factor of Safety (FoS)?

Answer:
FoS is the ratio of ultimate stress to working or allowable stress.

$stress\text{FoS} = \frac{\text{Ultimate stress}}{\text{Working stress}}$

It ensures the structure can withstand unexpected loads.

Q9. What is Shear Stress?

Answer:
Shear stress acts parallel to the surface. It’s defined as the force per unit area that causes one layer of material to slide over another.

$τ=FA\tau = \frac{F}{A}$

Q10. What is the difference between Axial Load and Eccentric Load?

Answer:

Axial Load: Acts along the centroidal axis of a member.
Eccentric Load: Acts away from the axis and induces bending in addition to direct stress.

Mechanical Properties Interview Questions and Answers

Understanding the mechanical properties of materials is crucial in Strength of Materials. These properties define how a material behaves under stress and are often discussed in design, failure analysis, and material selection during interviews.

Q11. What is Ductility?

Answer:
Ductility is the ability of a material to undergo significant plastic deformation before rupture. It is measured by percentage elongation or reduction in area during a tensile test.
Example: Copper, Mild Steel

Q12. What is Toughness?

Answer:
Toughness is the ability of a material to absorb energy and plastically deform without fracturing. It is the area under the stress-strain curve.
Tough materials are both strong and ductile.

Q13. Define Hardness.

Answer:
Hardness is the resistance of a material to indentation, scratching, or abrasion. Common tests include:

Brinell
Vickers
Rockwell

Q14. What is Resilience?

Answer:
Resilience is the capacity of a material to absorb energy when it is deformed elastically and release that energy upon unloading.
It is measured by the area under the elastic portion of the stress-strain curve.

Q15. What is Brittleness?

Answer:
Brittleness is the inability of a material to undergo plastic deformation before fracture.
Example: Glass, Cast Iron

Q16. What is Malleability?

Answer:
Malleability is the ability of a material to deform under compressive stress without cracking often associated with metals that can be rolled into thin sheets.
Example: Gold, Aluminum

Q17. What is Fatigue?

Answer:
Fatigue is the failure of a material due to repeated cyclic loading, even if the stress is below the material’s yield strength.
Fatigue failure occurs without warning after a number of cycles.

Q18. What is Creep?

Answer:
Creep is the slow, time-dependent deformation of a material under constant stress, usually at high temperature.
Common in turbine blades, engines, and boilers.

Q19. What is the difference between Engineering Stress and True Stress?

Answer:

Type	Formula	Description
Engineering Stress	$FA0\frac{F}{A_0}$	Based on original cross-sectional area
True Stress	$FAinstantaneous\frac{F}{A_{instantaneous}}$	Based on actual area as material necks

Q20. What is the Modulus of Rigidity?

Answer:
Also called Shear Modulus (G), it is the ratio of shear stress to shear strain:

$\frac{\tau}{\gamma}$

It measures the material’s resistance to shear deformation.

Stress & Strain Interview Questions and Answers

This section covers core principles of stress, strain, strain energy, and design safety crucial topics in Strength of Materials. These are highly technical and appear frequently in both oral interviews and technical exams.

Q21. What are the types of stress in Strength of Materials?

Answer:
The main types of stress include:

Tensile Stress – Pulling force (e.g., stretching a rod)
Compressive Stress – Pushing force (e.g., in columns)
Shear Stress – Force acting parallel to surface
Bending Stress – Occurs due to moments in beams
Torsional Stress – Produced by twisting shafts

Q22. What is strain energy?

Answer:
Strain energy is the energy stored in a body due to deformation. It is recovered when the load is removed (within the elastic limit).
For axial load:

$\frac{1}{2} \times \sigma \times \varepsilon \times V$

$\frac{P^2 L}{2AE}$

Q23. What is proof resilience?

Answer:
Proof resilience is the maximum strain energy stored per unit volume without permanent deformation.
Modulus of resilience is:

$Resilience=σ22E\text{Resilience} = \frac{\sigma^2}{2E}$

Q24. What is the stress-strain diagram for ductile materials?

Answer:
It shows:

Proportional Limit
Elastic Limit
Yield Point
Ultimate Stress
Breaking Point

Key features: Long plastic region, high strain before fracture.
Example: Mild steel.

Q25. Define Yield Stress and Ultimate Stress.

Answer:

Yield Stress: Stress at which a material starts to deform plastically.
Ultimate Stress: Maximum stress material can withstand before necking or fracture.

Q26. What is the working stress and how is it related to Factor of Safety?

Answer:
Working stress is the stress allowed in the design:

$StressFoS\text{Working Stress} = \frac{\text{Ultimate Stress}}{\text{FoS}}$

It ensures safety under service loads.

Q27. What is thermal stress?

Answer:
Thermal stress is developed in a body when its temperature changes and expansion or contraction is restricted.

$σ=E⋅α⋅ΔT\sigma = E \cdot \alpha \cdot \Delta T$

Where:

$α\alpha$ : Coefficient of thermal expansion
$ΔT\Delta T$ : Temperature change

Q28. What is volumetric strain?

Answer:
Volumetric strain is the change in volume divided by the original volume of a body.

$strain=εx+εy+εz\text{Volumetric strain} = \varepsilon_x + \varepsilon_y + \varepsilon_z$

For axial loading:

$εvol=ε(1−2ν)\varepsilon_{vol} = \varepsilon (1 – 2\nu)$

Bending & Shear Interview Questions and Answers

Bending and shear concepts are fundamental for beam design, structural analysis, and load-bearing components. This section is especially important for civil and mechanical engineering interviews.

Q29. What is a bending moment?

Answer:
A bending moment is the internal moment developed in a beam due to external loads that tend to bend the beam.
It is the product of force and perpendicular distance from a point:

$\times d$

Q30. What is a shear force?

Answer:
Shear force is the internal force developed along the cross-section of a beam that acts parallel to the surface. It arises from external loads trying to slide one part of the beam over another.

Q31. What is a Shear Force Diagram (SFD)?

Answer:
A Shear Force Diagram shows the variation of shear force along the length of a beam.
It helps locate maximum shear and points of zero shear (which could be points of max bending moment).

Q32. What is a Bending Moment Diagram (BMD)?

Answer:
A Bending Moment Diagram represents how bending moment varies along the length of the beam.
It is crucial for identifying:

Maximum bending moment
Points of zero moment
Beam behavior under load

Q33. What is the Point of Contraflexure?

Answer:
It is the point along a beam where the bending moment is zero, and the sign of moment changes (from positive to negative or vice versa).
Usually occurs in overhanging beams or continuous beams.

Q34. What is the difference between a simply supported beam and a cantilever beam?

Answer:

Beam Type	Support Conditions	Examples
Simply Supported Beam	Supported at both ends, free to rotate	Bridge beams
Cantilever Beam	Fixed at one end, free at the other	Balcony projections

Q35. What are the common types of beam supports?

Answer:

Fixed support – Restrains translation and rotation
Hinged or pinned support – Allows rotation, no translation
Roller support – Allows rotation and horizontal movement
These define the beam’s reaction types and equations of equilibrium.

Torsion & Shaft Interview Questions and Answers

Torsion deals with twisting of shafts and structural elements. It’s a critical topic for machine design, power transmission systems, and mechanical component analysis. Understanding torsion helps in designing safe rotating shafts and couplings.

Q36. What is torsion in mechanics?

Answer:
Torsion is the twisting of an object due to applied torque. It produces shear stress in the material, and the degree of twist depends on material properties and geometry.

Q37. What is the torsion equation?

Answer:
The torsion equation relates torque, shear stress, and angular twist:

$TJ=τr=GθL\frac{T}{J} = \frac{\tau}{r} = \frac{G\theta}{L}$

Where:

$T$ = Torque
$J$ = Polar moment of inertia
$τ\tau$ = Shear stress
$r$ = Radius
$G$ = Modulus of rigidity
$θ\theta$ = Angle of twist
$L$ = Length of shaft

Q38. What is the polar moment of inertia?

Answer:
The polar moment of inertia (J) is a measure of an object’s resistance to torsional deformation. For a circular shaft:

$\frac{\pi d^4}{32}$

It plays the same role in torsion as the area moment of inertia (I) in bending.

Q39. What is the difference between solid and hollow shafts?

Answer:

Property	Solid Shaft	Hollow Shaft
Weight	Heavier	Lighter for same strength
Strength	Slightly more	Comparable if properly designed
Cost	Cheaper	Slightly more expensive
Applications	Simple drives	Automobiles, aerospace, windmills

Hollow shafts offer better strength-to-weight ratio and save material.

Q40. What are the common types of shaft couplings?

Answer:

Rigid coupling – Connects two aligned shafts
Flexible coupling – Allows some misalignment
Oldham coupling – For parallel misaligned shafts
Universal joint – For angular misalignments

Couplings are used to transmit torque and accommodate misalignments.

Deflection of Beams Interview Questions and Answers

Deflection refers to how much a beam or structure bends under loading. Accurate knowledge of beam deflection is crucial for ensuring serviceability, comfort, and structural performance especially in buildings, bridges, and machines.

Q41. What is beam deflection?

Answer:
Deflection is the displacement of a point on a beam from its original position due to applied loads.
Excessive deflection can lead to serviceability issues or failure even if the structure doesn’t break.

Q42. What are the common methods to calculate beam deflection?

Answer:

Double Integration Method
Macaulay’s Method
Moment Area Method
Conjugate Beam Method
Virtual Work Method

Choice of method depends on load type and support conditions.

Q43. What is the standard deflection formula for a simply supported beam with central point load?

Answer:

$δmax=WL348EI\delta_{max} = \frac{W L^3}{48 E I}$

Where:

$W$ = Load at center
$L$ = Span length
$E$ = Young’s modulus
$I$ = Moment of inertia of beam cross-section

Q44. What factors affect the deflection of a beam?

Answer:

Type and magnitude of load
Span length (L) – longer beams deflect more
Material property (E) – stiffer materials deflect less
Cross-section (I) – larger moments of inertia reduce deflection
Boundary/support conditions

Columns & Buckling Interview Questions and Answers

Columns are structural elements that carry axial compressive loads. Buckling and instability are key concerns in column design, and interviewers often test your understanding of Euler’s theory, failure modes, and slenderness ratios.

Q45. What is buckling in columns?

Answer:
Buckling is the sudden lateral deflection of a column under axial compressive load. It occurs without material failure, and is a stability problem. It usually happens in long, slender columns.

Q46. State Euler’s formula for critical buckling load.

Answer:

$Pcr=π2EI(Leff)2P_{cr} = \frac{\pi^2 E I}{(L_{eff})^2}$

Where:

$P_{cr}$ = Critical or buckling load
$E$ = Young’s Modulus
$I$ = Moment of inertia
$L_{eff}$ = Effective length of the column

Q47. What is slenderness ratio?

Answer:
Slenderness ratio is:

$λ=Leffr\lambda = \frac{L_{eff}}{r}$

Where:

$L_{eff}$ = Effective length of the column
$r$ = Radius of gyration
A high slenderness ratio means the column is more prone to buckling.

Q48. What are the different types of column failure?

Answer:

Crushing failure – In short, stout columns (material fails in compression)
Buckling failure – In long, slender columns (instability failure)
Combined failure – In intermediate-length columns

Real-World / Scenario-Based SOM Interview Questions

These questions assess your application skills and ability to solve practical design and failure problems. They are especially common in core industry interviews, PSU exams, and final-year engineering project reviews.

Q49. You are designing a bridge beam. What factors will you consider for selecting the material and cross-section?

Answer:

Load type & magnitude (dead load, live load, dynamic load)
Span length
Material properties – High strength, durability, corrosion resistance
Cost and availability
Environmental conditions (e.g., wind, temperature)
Cross-section shape – I-beams or box girders for maximum moment resistance
Factor of Safety (FoS) for structural integrity

Q50. A steel rod under axial tension is showing plastic deformation. What could be the possible reasons?

Answer:

Load has exceeded the yield strength of steel
Incorrect cross-sectional area selected during design
Material may have residual stresses or flaws
Temperature effects causing thermal expansion
Lack of proper FoS consideration in design

Q51. How would you minimize deflection in a long beam without increasing material cost significantly?

Answer:

Increase moment of inertia (I) by optimizing beam cross-section (e.g., use I-section)
Use better support conditions, like fixed instead of simply supported
Reduce span using intermediate supports
Use pre-stressed members in critical areas
Distribute loads more uniformly

Q52. A column is failing by buckling. How can you redesign it to increase its capacity?

Answer:

Reduce effective length by altering support condition (e.g., fix both ends)
Increase cross-sectional moment of inertia (I)
Use a material with higher Young’s modulus (E)
Reduce slenderness ratio by increasing diameter or changing shape
Use bracing to reduce effective length
Use composite sections (e.g., concrete-filled steel tubes)

Tips to Crack Strength of Materials (SOM) Interviews

Want to leave a solid impression in your next technical interview? Follow these expert-backed tips:

1. Master Fundamental Concepts

Make sure you thoroughly understand:

Stress-strain behavior
Bending and torsion equations
Shear force and bending moment diagrams
Column stability and buckling

2. Revise Formulas & Diagrams

Prepare a quick cheat sheet with all important SOM formulas and standard diagrams (like BMD, SFD, Stress-Strain Curve, etc.). Diagrams often help you explain better during viva or technical rounds.

3. Practice Numerical Questions

Interviewers often ask small numerical problems to test your application skills. Be prepared to solve quick deflection, bending, or axial load problems.

4. Explain with Real-World Analogies

Don’t just give textbook answers. Try comparing beams to bridges, columns to pillars, or torsion to twisted rods. It shows clarity of concept.

5. Be Clear with Assumptions

Always state assumptions during design-oriented questions. For example, mention whether the load is static or dynamic, supports are ideal or practical, material is isotropic or not, etc.

6. Stay Confident, Even If You Don’t Know Everything

If you forget a formula or concept, explain what you know around it instead of saying “I don’t know.” It shows you’re analytical and calm under pressure.

Conclusion

Strength of Materials is one of the most foundational subjects for engineers. Whether you’re preparing for campus placements, PSU exams, core job interviews, or higher studies, mastering SOM gives you a serious edge.

In this guide, we’ve covered: