Core technical questions
"Explain the difference between stress and strain." Stress is force per unit area (Pascals): the internal forces within a material under external loads. Strain is the resulting deformation: change in length divided by original length (dimensionless). The relationship between them is material-dependent: in the elastic range, Young's modulus (E = stress/strain) describes it. Beyond the yield point the material deforms plastically. Understanding the full stress-strain curve (elastic region, yield point, ultimate tensile strength, fracture) is fundamental mechanical engineering knowledge. "What is fatigue failure and how do you design against it?" Fatigue failure occurs when a component fractures due to repeated cyclic loading at stresses below the static yield strength. Design against it: use S-N curves to determine fatigue life at a given stress range, apply appropriate safety factors, minimise stress concentrations (smooth fillets, no surface defects), specify surface treatment (shot peening, case hardening), and use FEA to identify high-stress regions.
Design and CAD questions
"Describe your design process for a new mechanical component." Requirements definition (loads, environment, cost, manufacturing constraints), conceptual design, analysis (hand calculations first, FEA for detailed validation), material selection, detail design and CAD modelling (name your tools: SolidWorks, CATIA, Creo, NX), drawing and tolerancing, design review, prototype and test. Design iteratively and validate assumptions with analysis. "How do you select a material for a structural application?" Define requirements (strength-to-weight ratio, corrosion resistance, temperature range, cost, manufacturability), use material selection tools (Ashby charts, Granta CES), shortlist and evaluate against all requirements, consider manufacturing route (machined, cast, additive, composite), and in 2026 also consider embodied carbon and recyclability.
Simulation and analysis questions
"Have you used FEA and what limitations did you have to be aware of?" Name the FEA software you have used (ANSYS, Abaqus, SolidWorks Simulation, Nastran). Key limitations: results are only as good as the mesh quality, boundary conditions, and material model. Validate against hand calculations or physical tests for critical applications. Run mesh convergence studies to confirm results are not mesh-dependent. Contact modelling (bolted joints, press fits) requires careful setup. FEA tells you where stresses are high; engineering judgment tells you whether the result is physically credible.
Behavioral questions
"Tell me about a design that failed or did not work as expected." Strong answer: specific design, specific failure mode, root cause investigation method, and what changed as a result. Engineers who have learned from failure are more valuable than those who claim to never have failed. "Describe a time you worked in a cross-functional team to deliver an engineering project." Your specific role, how you worked with non-engineers (procurement, manufacturing, quality, commercial), what communication challenges arose, and how the collaboration improved the outcome.