Question 1

Equating maximum bending and maximum shear stresses in a circular shaft  A circular shaft of diameter D is subjected simultaneously to a bending moment M and a twisting moment T. If the maximum bending stress equals the maximum torsional shear stres…

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Introduction / Context: Combined bending and torsion occur frequently in shafts with pulleys or gears. Comparing bending and torsional stresses helps in establishing allowable combined loading or determining an equivalent moment. Given Data / Assumptions: Solid circular shaft of diameter D. Elastic behavior; standard bending and torsion formulas apply. Condition: σ_max(bending) = τ_max(torsion). Concept / Approach: Maximum bending normal stress is σ_max = M c / I with c = D/2 and I = π D^4 / 64. Maximum torsional shear stress is τ_max = T c / J with J = π D^4 / 32. Step-by-Step Solution: σ_max = M (D/2) / (π D^4 / 64) = 32 M / (π D^3).τ_max = T (D/2) / (π D^4 / 32) = 16 T / (π D^3).Set σ_max = τ_max → 32 M / (π D^3) = 16 T / (π D^3).Therefore 32 M = 16 T → M = T / 2. Verification / Alternative check: Dimensional and numerical consistency checks confirm the relation. If T doubles M, stresses match by the constants above. Why Other Options Are Wrong: Any relation other than M = T/2 violates the established proportionality between bending and torsional stress constants for a circular section. Common Pitfalls: Using radius instead of diameter in I and J; mixing formulas for hollow shafts; forgetting the different constants (64 vs 32) in I and J. Final Answer: M = T/2

Question 2

Axial deformation under self-weight vs. equivalent end load: For a uniform vertical bar, how does the elongation caused by its own weight compare with the elongation produced if the same total weight is applied as a single axial load at the free end?

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Introduction / Context: Designers often compare axial deformation due to self-weight with the deformation caused by a lumped end load. Recognizing the correct relationship avoids overestimating or underestimating elongation in hanging members such as tie rods, cables, and tall columns. Given Data / Assumptions: Uniform prismatic bar of length L, cross-sectional area A, density rho, and modulus E. Self-weight W = rho * g * A * L acts continuously along the length. Comparison is with a concentrated end load equal to W. Linear elasticity, small deformation, axial loading only. Concept / Approach: Deformation is the integral of strain along the bar. For a concentrated end load W, the axial force is constant everywhere, giving a simple expression. For self-weight, axial force varies linearly from zero at the free end to W at the top, so the average internal force is W/2, leading to half the elongation of the same bar under end load W. Step-by-Step Solution: End load case: delta_end = (W * L) / (A * E)Self-weight case: internal force at distance x from free end is rho * g * A * xElongation: delta_sw = ∫(0→L) [rho * g * A * x / (A * E)] dx = (rho * g / E) * (L^2 / 2)But W = rho * g * A * L ⇒ delta_sw = (W * L) / (2 * A * E) = 0.5 * delta_end Verification / Alternative check: The self-weight produces a linearly varying force with an average of W/2, so elongation equals that from a constant force of W/2 applied along the length, confirming the half relation. Why Other Options Are Wrong: Equal to/double/quadruple/one-third contradict the integral result and average-force reasoning. Common Pitfalls: Using W instead of the varying internal force in the integral; forgetting that the free end carries zero axial force in the self-weight case. Final Answer: half

Question 3

Elastic constants relationship: For a material with Poisson’s ratio ν = 0.4, what is the ratio of shear modulus to Young’s modulus (G/E)?

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Introduction / Context: In isotropic linear elasticity, the independent constants E (Young’s modulus), G (shear modulus), and ν (Poisson’s ratio) are linked. Converting between them is routine in strength of materials and finite element modeling. Given Data / Assumptions: Isotropic, homogeneous material. Poisson’s ratio ν = 0.4. Standard elastic relation G = E / [2 * (1 + ν)]. Concept / Approach: Use the canonical relationship connecting E, G, and ν. Substituting ν directly gives the ratio without needing absolute values of E or G. Step-by-Step Solution: G = E / [2 * (1 + ν)]With ν = 0.4 ⇒ 1 + ν = 1.4G/E = 1 / [2 * 1.4] = 1 / 2.81 / 2.8 = 0.357142… = 5 / 14 Verification / Alternative check: Sanity check: For ν between 0 and 0.5, G/E should lie between 1/3 and 1/2.8; 5/14 ≈ 0.357 fits the expected range. Why Other Options Are Wrong: 5/7, 7/5, 14/5 are greater than 1, impossible for G/E with ν = 0.4. 2/5 = 0.4 does not match the exact relation for ν = 0.4. Common Pitfalls: Forgetting the 2 in the denominator; confusing G/E with E/G; using an incorrect ν value range that yields nonphysical ratios. Final Answer: 5/14

Question 4

Effect of axial compression (push) on dimensions: A rectangular bar of length l, width b, and thickness t is subjected to a compressive axial load P. Which dimensional change is correct (considering Poisson’s effect)?

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Introduction / Context: Poisson’s effect couples axial and lateral strains. Under compression (push), a bar shortens axially and tends to bulge laterally, a behavior crucial for fit tolerances, buckling, and contact problems. Given Data / Assumptions: Axial compressive load P along the length. Linear elastic material with positive Poisson’s ratio. Small deformations and uniform stress state. Concept / Approach: Axial compressive strain is negative, while lateral strains are positive and proportional to ν times the axial strain (with opposite sign). Hence, length decreases; width and thickness increase. Step-by-Step Solution: Axial strain: epsilon_long = -σ / E < 0Lateral strain: epsilon_lat = -ν * epsilon_long > 0Therefore: Δl < 0; Δb > 0; Δt > 0 Verification / Alternative check: Cylindrical compression tests and compression of rubber blocks visibly show shortening with lateral bulging, confirming the sign pattern of strains. Why Other Options Are Wrong: All dimensions increasing/decreasing contradicts Poisson’s coupling. Length increases (option C) is opposite to compression. Length unchanged (option E) is unrealistic under finite compressive stress. Common Pitfalls: Confusing tension and compression effects; ignoring small but significant lateral expansions that influence fits and clearances. Final Answer: length decreases, width and thickness increase

Question 5

Mohr’s circle interpretation: Is the maximum shear stress equal to the radius of Mohr’s circle for a plane-stress state?

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Introduction / Context: Mohr’s circle graphically represents stress transformation. The circle’s center, radius, and key points map directly to principal and shear stresses, providing intuitive insight into maximum values and orientations. Given Data / Assumptions: Plane-stress condition with σx, σy, and τxy. Standard sign convention and Mohr’s circle construction. Concept / Approach: The center of Mohr’s circle is at (σx + σy)/2. The radius equals sqrt( ((σx − σy)/2)^2 + τxy^2 ). The maximum in-plane shear stress is precisely this radius, occurring at the top and bottom of the circle (90° on Mohr’s circle, 45° in physical space from principal directions). Step-by-Step Solution: Center C = (σx + σy)/2Radius R = sqrt( ((σx − σy)/2)^2 + τxy^2 )Maximum shear stress τmax_in-plane = R Verification / Alternative check: From transformation equations, τ^2 + [σ − (σx + σy)/2]^2 = R^2. The peak shear equals the circle’s radius by geometry and by differentiation of the shear-stress transformation formula. Why Other Options Are Wrong: Restrictions to pure shear or σx = σy are unnecessary; the result holds generally in plane stress. “True for 3D only” is incorrect; a similar notion exists in 3D but here we address plane stress specifically. Common Pitfalls: Mixing up the diameter and radius; forgetting the 2:1 mapping between physical angle and Mohr angle; sign mistakes when plotting τxy. Final Answer: Correct

Question 6

Torsional rigidity identification: For a prismatic circular shaft, which expression represents torsional rigidity (torque per radian of twist over the full length)?

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Introduction / Context: Torsional rigidity characterizes how resistant a shaft is to twisting under applied torque. It is central to shaft design for power transmission, where angular deflection limits are specified in addition to strength. Given Data / Assumptions: Straight, prismatic shaft, length L, polar second moment J, shear modulus G. Linear elastic torsion: θ = T * L / (G * J). Concept / Approach: Rearranging the torsion formula shows torque per radian of twist (stiffness) equals GJ/L. Since T/θ = GJ/L, the expression T/θ directly represents torsional rigidity over the entire length (units: N·m/rad). Step-by-Step Solution: θ = (T * L) / (G * J)T / θ = (G * J) / LHence torsional rigidity = T / θ Verification / Alternative check: Dimension check: GJ/L has dimensions of torque per radian, consistent with stiffness. Numerical examples confirm proportionality between T and θ for given G, J, and L. Why Other Options Are Wrong: T/J and T/r are not stiffness measures. T/G has incorrect dimensions. G * J / L is a correct explicit form, but the option asked for an expression in terms of T and θ; thus T/θ is the matching choice. Common Pitfalls: Confusing section property J with polar radius r; mixing strength (τ = T r / J) with stiffness (θ relation). Final Answer: T / θ

Question 7

Composite shaft twist distribution: A circular shaft is fixed at A. Segment AB (first half of length) has diameter D; segment BC (second half) has diameter D/2. If the rotation of B relative to A is 0.1 rad, what is the rotation of C relative to B (…

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Introduction / Context: Angle of twist under torsion scales with length and inversely with polar second moment J. In stepped shafts, thin segments dominate angular rotation, which is vital for torsional deflection control in drivetrains and tool spindles. Given Data / Assumptions: Shaft fixed at A, torque constant along length. AB length = BC length = L/2. Diameters: D on AB; D/2 on BC. Rotation of B relative to A, θ_AB = 0.1 rad. Concept / Approach: Angle of twist: θ = T * L / (G * J). For solid circular shafts, J ∝ d^4. Thus, for equal lengths under same torque, the twist ratio equals the inverse ratio of d^4. Step-by-Step Solution: J_AB ∝ D^4; J_BC ∝ (D/2)^4 = D^4 / 16Twist per half: θ_BC / θ_AB = (L/2)/(J_BC) ÷ (L/2)/(J_AB) = J_AB / J_BC = 16Given θ_AB = 0.1 rad ⇒ θ_BC = 16 * 0.1 = 1.6 rad Verification / Alternative check: Total twist A→C would be 0.1 + 1.6 = 1.7 rad, showing the slender half dominates deflection, as expected. Why Other Options Are Wrong: 0.4, 0.8, 3.2, 0.2 rad do not match the 16× ratio dictated by d^4 scaling. Common Pitfalls: Using d^2 instead of d^4; forgetting lengths are equal; mixing up which segment twists more (the thinner segment twists far more). Final Answer: 1.6 rad

Question 8

Eccentric loading on a column: If the magnitudes of direct (uniform) stress and bending stress are equal, what happens to the stress at one extreme fibre of the column cross-section?

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Introduction / Context: Columns under eccentric axial load experience a combination of uniform direct stress and linear bending stress. Understanding superposition at the extreme fibres is essential for avoiding cracking or loss of compression on one side. Given Data / Assumptions: Direct axial stress σ0 = P / A (uniform). Bending stress σb = M * y / I (linear, tension on one side, compression on the other). Magnitudes: |σ0| = |σb| at extreme fibre (y = ymax). Concept / Approach: Total stress at any fibre equals σ = σ0 ± σb. At the compressed extreme, signs add; at the opposite extreme, they subtract. If magnitudes are equal, one side becomes zero stress (transition from compression to zero), indicating the brink of tension on that side for further eccentricity. Step-by-Step Solution: At one extreme: σ_extreme1 = σ0 + σbAt the other extreme: σ_extreme2 = σ0 − σbGiven |σ0| = |σb| ⇒ σ_extreme2 = 0 Verification / Alternative check: This condition corresponds to the load line passing through the core boundary (kern), where no tension just begins to occur. Any additional eccentricity produces tension at the relieved edge. Why Other Options Are Wrong: Doubling is incorrect; superposition may cancel on one side. Uniform stress cannot exist with bending. Neutral axis location, not maximum stress, occurs where stress is zero across the section; saying it is maximum at the neutral axis is nonsensical. Common Pitfalls: Forgetting sign conventions; assuming bending always increases stress magnitude at both edges; ignoring the eccentric load core concept. Final Answer: It is zero at one extreme fibre

Question 9

Units check in mechanics of materials: What is the unit of (engineering) strain for axial loading or bending?

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Introduction / Context: Dimensional consistency is critical in mechanics of materials. Strain represents deformation per unit length, used in Hooke’s law and failure criteria. Given Data / Assumptions: Engineering (normal) strain ε = ΔL / L. Shear strain γ is an angle in radians, also dimensionless. Concept / Approach: Because strain is a ratio of two lengths (or an angle measured in radians), it has no physical unit. It may be reported as a pure number, percentage, or microstrain for convenience, but fundamentally it is dimensionless. Step-by-Step Solution: ε = ΔL / L → [length] / [length] → dimensionlessγ ≈ tan θ (for small angles) → dimensionless Verification / Alternative check: Hooke’s law E = σ / ε shows E carries stress units (e.g., MPa) while ε is unitless, maintaining dimensional balance. Why Other Options Are Wrong: N-mm, N/mm, and MPa are force-length or stress units, not applicable to a ratio of lengths. mm is length, not a nondimensional ratio. Common Pitfalls: Confusing strain with elongation (which has units); writing “mm/mm” and then treating it as “mm” rather than recognizing it cancels to a pure number. Final Answer: no unit

Question 10

Volumetric stiffness definition: A body is subjected to equal direct stresses in three mutually perpendicular directions (hydrostatic state). The ratio of direct stress to the corresponding volumetric strain is called:

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Introduction / Context: When a material experiences uniform pressure from all directions, it changes volume without shape distortion. The proportionality constant relating pressure (direct stress) to volumetric strain defines the material’s resistance to uniform compression. Given Data / Assumptions: Hydrostatic (triaxial) state: σx = σy = σz. Small strains and linear elasticity. Concept / Approach: Bulk modulus K is defined as K = hydrostatic stress / volumetric strain. It complements Young’s modulus (uniaxial response) and shear modulus (distortional response without volume change). Step-by-Step Solution: Volumetric strain: ε_v = ΔV / VUnder equal direct stresses: K = σ_h / ε_vHence the correct term is bulk modulus. Verification / Alternative check: Thermodynamics and wave-propagation relations (e.g., speed of sound in solids) also rely on K, further confirming its definition for volumetric response. Why Other Options Are Wrong: Young’s modulus relates axial stress to axial strain. Modulus of rigidity (G) relates shear stress to shear strain. Poisson’s ratio is the negative ratio of lateral to axial strain in uniaxial loading. Common Pitfalls: Confusing K with E due to both being “stiffness” measures; forgetting that K governs volume change, not shape distortion. Final Answer: bulk modulus

Question 11

Helical spring geometry: A closely coiled helical spring has mean coil diameter D and wire diameter d. The spring index is defined as which of the following ratios?

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Introduction / Context: The spring index (C) indicates coil tightness and manufacturability of helical springs. It affects stress concentration, buckling tendency, and ease of coiling, influencing both performance and cost. Given Data / Assumptions: Mean coil diameter = D; wire diameter = d. Close-coiled helical spring under typical axial loading. Concept / Approach: By definition, spring index C = D / d. Typical design ranges (e.g., 6 ≤ C ≤ 12) balance stress concentration and manufacturability. Very low C increases stress concentration and makes coiling difficult; very high C can cause instability. Step-by-Step Solution: Define C = D / d.Interpretation: larger C means relatively large coil diameter for a given wire thickness. Verification / Alternative check: Standard design equations for Wahl factor and spring stress include C = D/d explicitly, confirming the accepted definition. Why Other Options Are Wrong: 1/d, 1/D, and D * d do not match the accepted definition. d/D is the reciprocal and would misrepresent coil tightness. Common Pitfalls: Mixing mean diameter with outer or inner diameter; using reciprocal by mistake when calculating stress correction factors. Final Answer: D / d

Question 12

Design of riveted joints – Tearing of plate across a pitch length What is the pull required to tear off the plate per pitch length? (Use: p = pitch of rivets, t = plate thickness, σt, τ, σc = permissible tensile, shear, and crushing stresses respect…

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Introduction / Context: In riveted joint design, the plate between successive holes can fail in tension. For safe design, we compare the tensile tearing strength of the net section with alternative modes such as rivet shear and bearing (crushing). This question asks for the standard expression of the tensile (tearing) resistance of the plate across one pitch length. Given Data / Assumptions: p = pitch of rivets (centre-to-centre distance along load direction). t = plate thickness. d = diameter of rivet hole (net width reduction equals d). σt, τ, σc are permissible stresses in tension, shear, and crushing respectively. Single line of holes considered for tearing across one pitch. Concept / Approach: The tearing plane passes through the net cross-section of the plate between the two adjacent holes. The effective (net) width resisting tension equals (p − d). The tearing strength is tensile stress times net area. Step-by-Step Solution: Net width resisting tension = (p − d).Net area resisting tension = (p − d) * t.Tearing (tensile) resistance of plate = (p − d) * t * σt. Verification / Alternative check: Design checks compare three capacities per pitch: tearing of plate = (p − d) * t * σt; shearing of rivets (single or double shear) = number_of_shear_planes * (π d^2 / 4) * τ; bearing (crushing) = d * t * σc. The smallest governs design and also sets the efficiency. Why Other Options Are Wrong: (p − 2d) * t * σc uses bearing stress and incorrect net width; (p − d) * t * τ uses shear stress on a plate tension mode; (2p − d) * t * σt is not a recognized pitch-based expression; p * t * σt ignores the hole completely. Common Pitfalls: Using rivet nominal diameter instead of hole diameter for net width; confusing pitch with margin; mixing up stress symbols (σt vs τ vs σc). Final Answer: (p - d) * t * σt

Question 13

Thin cylindrical shell under internal pressure The volumetric strain of a thin cylinder is expressed in terms of hoop strain ε1 and longitudinal strain ε2 as:

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Introduction / Context: For thin cylindrical pressure vessels, internal pressure produces hoop and longitudinal stresses, leading to corresponding strains. The overall volume change (volumetric strain) is the sum of normal strains along three mutually perpendicular directions. Given Data / Assumptions: Thin cylinder with diameter much larger than thickness (membrane theory). Principal strains: hoop (circumferential) ε1, longitudinal (axial) ε2. Radial strain is negligible in thin-shell theory compared to hoop and longitudinal components. Concept / Approach: Volumetric strain in small-deformation theory equals the algebraic sum of strains in three orthogonal directions. A thin cylinder has two identical circumferential directions around the axis (hoop in two orthogonal tangential directions) and one longitudinal direction along the axis. Step-by-Step Solution: Volumetric strain, ε_v ≈ ε_x + ε_y + ε_z.For a cylinder: two circumferential (hoop) directions → ε_x = ε_y = ε1; one longitudinal direction → ε_z = ε2.Therefore, ε_v = ε1 + ε1 + ε2 = 2 ε1 + ε2. Verification / Alternative check: Using stress/strain relations, ε1 and ε2 can be computed from hoop and longitudinal stresses. Substituting those into the sum still yields ε_v = 2 ε1 + ε2. Why Other Options Are Wrong: Expressions with minus signs would imply volume decreases with positive tensile strains, which contradicts basic strain superposition; ε1 + ε2 ignores the second circumferential direction. Common Pitfalls: Counting only one hoop direction; including radial strain in thin-shell problems where it is negligible. Final Answer: 2 ε1 + ε2

Question 14

Beam types – identification by support conditions A beam that is fixed at one end and free at the other is called:

Accepted Answer

Introduction / Context: Structural analysis begins with recognizing beam support conditions, since bending moments, shear forces, slopes, and deflections depend on how the beam is restrained. Given Data / Assumptions: One end built-in (encastré: zero slope and zero deflection). Other end free (no support reactions). Linearly elastic, prismatic beam. Concept / Approach: Standard beam types include simply supported (pin–roller), fixed beam (both ends fixed), cantilever (one end fixed, other free), overhanging (span extends beyond a support), and continuous (more than two supports). Correct naming ensures correct use of formulas. Step-by-Step Identification: Check restraints: fixed at one end implies encastré support.Opposite end is free → no restraint → classic cantilever configuration. Verification / Alternative check: Moment and slope diagrams for standard loads (point load at free end, uniform load, etc.) match cantilever beam solutions: maximum moment at the fixed end, zero at the free end. Why Other Options Are Wrong: Simply supported has rotation allowed at both ends; fixed beam is fixed at both ends; overhanging beams have spans extending beyond supports; continuous beams have three or more supports. Common Pitfalls: Confusing cantilever with a propped cantilever (one end fixed, one end simply supported) or with an overhang case. Final Answer: Cantilever beam

Question 15

Fixed–fixed beam under uniformly distributed load For a fixed beam of length l carrying a total load W uniformly distributed over the whole span, what is the maximum deflection?

Accepted Answer

Introduction / Context: Deflection control is a key serviceability requirement in beams. End fixity significantly reduces midspan deflection compared to simply supported conditions. This problem asks for the maximum deflection of a fixed–fixed beam under a uniformly distributed load (UDL) expressed in terms of total load W. Given Data / Assumptions: Span = l; flexural rigidity = E I (constant). Uniformly distributed load of intensity w (so total W = w l). Both ends fully fixed (zero rotation and zero deflection). Concept / Approach: Standard closed-form results from beam theory: for a fixed–fixed beam under UDL w, the maximum deflection at midspan is y_max = w l^4 / (384 E I). Converting using W = w l gives y_max = W l^3 / (384 E I). Step-by-Step Solution: Start with y_max = w l^4 / (384 E I) for fixed–fixed with UDL.Replace w by W / l (since W = w l).Therefore y_max = (W / l) * l^4 / (384 E I) = W l^3 / (384 E I). Verification / Alternative check: Compare with simply supported beam under the same total load: y_max,SS = 5 W l^3 / (384 E I). The fixed–fixed deflection is one-fifth of the simply supported value, consistent with increased restraint. Why Other Options Are Wrong: 5 W l^3 / (384 E I) is the simply supported case; W l^3 / (48 E I) and W l^3 / (192 E I) correspond to other loading/support cases; W l^4 / (8 E I) has wrong dimensions and matches a cantilever UDL form when expressed in w and l. Common Pitfalls: Mixing up w and W; applying simply supported formulas to fixed beams; forgetting to convert intensity to total load. Final Answer: W l^3 / (384 E I)

Question 16

Cantilever with a point load at the free end For a cantilever beam of length l carrying a point load W at the free end, what is the maximum deflection?

Accepted Answer

Introduction / Context: Cantilever beams are common in brackets, balconies, and machine elements. Knowing standard deflection formulas allows quick checks on stiffness and serviceability. Given Data / Assumptions: Cantilever length l, flexural rigidity E I constant. Point load W applied at the free end. Small deflection, linear elastic behavior. Concept / Approach: From Euler–Bernoulli beam theory, slope and deflection are obtained by integrating the curvature equation M / (E I) = d^2 y / d x^2 with appropriate boundary conditions (zero deflection and slope at the fixed end). Step-by-Step Solution: Bending moment diagram for a free-end point load: M(x) = −W (l − x).Integrate twice and apply y(0) = 0 and dy/dx at x = 0 equals 0.Resulting maximum deflection at the free end: y_max = W l^3 / (3 E I). Verification / Alternative check: Compare with UDL on cantilever (y_max = w l^4 / (8 E I)); magnitudes are consistent for typical l and loadings. Why Other Options Are Wrong: W l^3 / (48 E I) is associated with simply supported configurations; W l^2 / (2 E I) has incorrect dimensions; W l^4 / (8 E I) corresponds to UDL on a cantilever; 2 W l^3 / (3 E I) is off by a factor of 2. Common Pitfalls: Forgetting boundary conditions at the fixed end; confusing cantilever formulas with simply supported ones. Final Answer: W l^3 / (3 E I)

Question 17

Simple bending theory – meaning of “plane sections remain plane” In the assumptions of Euler–Bernoulli beam theory, the statement “plane sections before bending remain plane after bending” implies that:

Accepted Answer

Introduction / Context: Euler–Bernoulli simple bending theory relies on kinematic assumptions to relate curvature, strain, and stress. Understanding “plane sections remain plane” is essential for deriving linear strain distributions. Given Data / Assumptions: Prismatic beam, small deflections. Normals to the neutral surface remain straight and rotate but do not warp. Shear deformation is neglected (classical beam theory). Concept / Approach: If a cross-sectional plane remains plane after bending, all points on a line normal to the neutral axis experience the same rotation, leading to a linear variation of longitudinal displacement with distance from the neutral axis, hence a linear strain distribution. Step-by-Step Reasoning: Assume a radius of curvature R for the neutral surface.A fiber at a distance y from the neutral axis changes length in proportion to y.Thus, axial strain ε_x = y / R, which is linear in y (proportional to distance from the neutral axis). Verification / Alternative check: Using Hooke’s law σ_x = E ε_x, the stress distribution also becomes linear in y, not uniform. That matches classic linear bending stress σ = M y / I. Why Other Options Are Wrong: Stress uniformity (a) contradicts bending; (b) strain uniform is incorrect; (e) shear strain is not necessarily zero in reality—it is neglected only in the kinematic assumption for bending response. Common Pitfalls: Confusing linear strain (correct) with linear stress being the original assumption; in fact linear stress results from linear strain plus Hooke’s law. Final Answer: Strain is proportional to the distance from the neutral axis

Question 18

Thick cylinder under internal pressure – Minimum hoop (tangential) stress at outer surface A thick cylindrical shell with inner radius r_i and outer radius r_o is subjected to internal pressure p only. What is the tangential (hoop) stress at the out…

Accepted Answer

Introduction / Context: In thick-walled cylinders, stresses vary across the wall thickness. Lame’s equations provide closed-form expressions for radial and hoop stresses. The outer-surface hoop stress is the minimum tangential stress for internal-pressure-only loading. Given Data / Assumptions: Internal pressure p; no external pressure. Inner radius r_i, outer radius r_o. Elastic, isotropic, axisymmetric conditions. Concept / Approach: Lame’s solutions: σ_r = A − B / r^2 and σ_θ = A + B / r^2. Apply boundary conditions σ_r(r_i) = −p and σ_r(r_o) = 0 to find constants A, B, then evaluate σ_θ at r = r_o. Step-by-Step Solution: From σ_r(r_o) = 0 ⇒ A = B / r_o^2.From σ_r(r_i) = −p ⇒ B / r_o^2 − B / r_i^2 = −p ⇒ B = p r_o^2 r_i^2 / (r_o^2 − r_i^2).Thus A = B / r_o^2 = p r_i^2 / (r_o^2 − r_i^2).Hoop stress at outer surface: σ_θ(r_o) = A + B / r_o^2 = 2 p r_i^2 / (r_o^2 − r_i^2). Verification / Alternative check: Compare with inner-surface hoop stress σ_θ(r_i) = 2 p r_o^2 / (r_o^2 − r_i^2), which is larger; hence σ_θ decreases from inner to outer surface, matching expectations. Why Other Options Are Wrong: (a) corresponds to a different combination; (c) hoop stress is not zero at the outer surface (radial stress is zero there); (d) and (e) are not consistent with Lame’s boundary conditions. Common Pitfalls: Confusing radial stress with hoop stress; sign conventions; mixing r and r^2 in algebra. Final Answer: σ_θ(r_o) = 2 p r_i^2 / (r_o^2 − r_i^2)

Question 19

Simply supported beam with symmetric, zero-end, maximum-at-centre triangular load For a simply supported beam carrying a distributed load that varies from zero at both ends to w per metre at the centre (symmetric triangular), the location of maximum…

Accepted Answer

Introduction / Context: In beams with non-uniform distributed loads, the maximum bending moment occurs where the shear force crosses zero. For a symmetric triangular load peaking at midspan and vanishing at the supports, determining the location is key to design. Given Data / Assumptions: Simply supported beam, symmetric load w(x) increasing to a maximum at midspan and decreasing to zero at both ends. Linear elastic behavior; standard sign conventions. Concept / Approach: Shear force V(x) is the integral of −w(x), and bending moment M(x) is the integral of V(x). For a symmetric loading about midspan, reactions are equal, and the shear diagram is antisymmetric about the centre. The location where V(x) = 0 under symmetric loading is the centre. Step-by-Step Reasoning: Because loading is symmetric, support reactions are equal.The shear force changes sign only once and, by symmetry, this occurs at the midspan.Therefore, M(x) reaches an extremum at midspan, which is the maximum bending moment for this case. Verification / Alternative check: Constructing the shear and moment diagrams analytically for a symmetric triangular load confirms V = 0 at midspan and M maximum there. Why Other Options Are Wrong: Quarter-span locations are typical for certain point or trapezoidal loadings, not this symmetric zero-end triangular case; at supports, moment is zero for simply supported beams. Common Pitfalls: Confusing the zero-shear point for asymmetric loads; assuming uniform load behavior (where maximum also occurs at midspan, but for different reasons). Final Answer: At the centre of the span

Question 20

Riveted joints – basic terminology and correct statements Which of the following statements is correct?

Accepted Answer

Introduction / Context: Clear terminology in riveted joints prevents design and fabrication errors. Common terms include pitch, margin (edge distance), and the basis for specifying a rivet. Given Data / Assumptions: Standard fabrication practice for structural and machine riveted joints. Nominal sizes refer to shank/nominal diameter unless stated otherwise. Concept / Approach: Rivets are ordered and identified by nominal (shank) diameter and length under the head. Hole sizes are slightly larger than rivet diameter to permit insertion. Pitch is the centre-to-centre distance along the load direction, while margin is the distance from a hole centre to the plate edge. Step-by-Step Reasoning: Identify the correct definition: specification by shank diameter is standard.Check others: hole size in plates is typically larger than rivet to allow driving; margin is not pitch; recommended pitch is generally much greater than 1.5 d (which is a typical minimum margin, not pitch). Verification / Alternative check: Design handbooks list pitches typically ≥ 2.5 d to 3 d or more depending on application, and margin commonly ≥ 1.5 d. Why Other Options Are Wrong: (a) Hole size is slightly greater, not less; (b) margin is edge distance, while pitch is centre-to-centre; (d) 1.5 d refers to minimum edge distance, not pitch; (e) head diameter is not the standard specification. Common Pitfalls: Interchanging terms pitch and margin; ordering rivets by the wrong size metric. Final Answer: Rivets are generally specified by their shank diameter

Strength of Materials Questions