Journal of Mechanical and Mechanics Engineering

Fatigue Failure Mechanisms in Critical Tubular Joints of Gulf of Guinea Jackets: S–N, Fracture Mechanics and Corrosion Ageing Interaction

Wali S. A — Tue, 29 Sep 2026 00:00:00 +0000

This paper analyses the fatigue failure mechanisms that govern the residual life of critical tubular joints on a representative Gulf of Guinea (GoG) steel jacket platform. Both the conventional S–N (Palmgren–Miner cumulative damage) and fracture-mechanics (Paris–Erdogan crack-growth) approaches are applied, with explicit inclusion of time-dependent corrosion and structural ageing effects. Six representative joints (J1–J6) are examined under realistic operational loading. Deterministic S–N calculations yield a 25-year damage ratio of 1.85 and an implied residual life of 13.5 years for the governing lower-bay K-joint (J5). Independent fracture-mechanics analysis, initiated from a representative surface crack depth a₀ = 0.5 mm, produces a crack-propagation life of 13.5 years for the same joint, confirming consistency between the two methodologies. Parametric studies incorporating corrosion rates in the range 0.1–0.4 mm/year demonstrate that progressive wall thinning and associated stress elevation reduce remaining fatigue life by 9%–28%. The results highlight the necessity of integrating corrosion-fatigue interaction into residual-life assessments of ageing GoG jackets and provide a validated basis for inspection prioritisation and life-extension decisions.

Productivity Improvement through Method Study and Work Measurement: A Structured Framework for Manufacturing Operations

V. K. Patel, Shrimali Aryan Nileshbhai — Fri, 09 Oct 2026 00:00:00 +0000

Productivity improvement is a central objective of every manufacturing organization, yet many plants look first to new equipment before examining how work is actually performed. Work study offers a systematic and low-capital alternative. It combines method study, which seeks a simpler and more effective way of doing a job, with work measurement, which establishes the time a qualified worker needs to do that job at a defined level of performance. This paper presents a structured study of productivity and work study in manufacturing operations: the definition and measurement of productivity, the basic procedure of method study and its recording techniques, micro- and macro-motion study with the principles of motion economy, work measurement by time study, work sampling and predetermined motion time systems, and an introduction to ergonomics. A functional classification maps each recording technique to the kind of inefficiency it exposes, and a worked time-study calculation with assumed values traces observed time through rating and allowances to standard time. An illustrative before-and-after comparison shows how a method improvement is converted into a quantified productivity gain. The classification indicates that unnecessary handling, idle time, and long movement are the highest-impact sources of lost productivity, that method study should precede work measurement, and that a consolidated checklist can support routine application of work study in a plant.

Design Analysis for a Pyramidal Steel Roof Truss Fabricated from Equal-Angle Sections

Kokoro Abraham Abraham, Arogo Eyaramuonan Charles — Mon, 19 Oct 2026 00:00:00 +0000

Steel angle-iron trusses remain one of the most widely used roofing solutions for institutional and residential buildings in Nigeria, valued for their light weight, ease of fabrication, and economy of material relative to reinforced-concrete alternatives. This study presents the structural design analysis and governing equations for a hip/pyramidal steel roof truss fabricated entirely from 50 mm × 50 mm × 5 mm mild-steel equal-angle sections, as set out in the accompanying isometric working drawing. The truss is idealized as a set of pin-jointed plane trusses decomposed from the pyramidal form, and the governing dead, live and wind loading equations are formulated in accordance with BS 6399 Parts 1 and 2. Member axial forces are obtained by the method of joints and verified by the method of sections, with free-body diagrams extracted from the working drawing to illustrate the equilibrium equations at each stage. Tension, compression, slenderness, connection, and deflection checks are then developed to BS 5950-1:2000, including the modified single-angle slenderness provisions relevant to angle members connected through one leg only. The resulting framework of 32 governing equations provides a complete, code-consistent basis for verifying the adequacy of the 50 × 50 × 5 mm angle for every member class shown in the drawing, and for re-sizing members where a check is not satisfied.

Modal Vibration Sensitivity to Anisotropic Stiffness Degradation in Composite Laminates: Implications for Fatigue Damage Assessment

Muhsin Aljuboury — Tue, 27 Oct 2026 00:00:00 +0000

Fatigue-induced damage in laminated composites can degrade individual elastic properties at different rates, producing mode-dependent changes in structural vibration characteristics. This study investigates whether intact-state modal sensitivities can predict the frequency response to finite anisotropic stiffness degradation without repeated degraded-state eigenvalue analyses. A component-resolved modal-sensitivity framework is derived from the generalized eigenvalue problem and extended to finite stiffness loss by integrating a logarithmic frequency–stiffness relation. The formulation is implemented using a first-order shear deformation theory (FSDT) finite-element model with nine-node quadratic elements. A unidirectional [0]₁₀ GFRP laminate is used to identify stiffness–mode relationships, while a symmetric cross-ply [0/90]_s laminate assesses predictor transferability. The numerical implementation and modal sensitivities are verified through analytical beam-limit comparisons and finite-difference calculations. For the unidirectional laminate, bending-dominated modes exhibit E₁ sensitivities of 0.493–0.498, whereas twisting-mode frequencies are primarily sensitive to G₁₂, with values of 0.443–0.459. For prescribed stiffness reductions up to 30%, conventional linear extrapolation produces maximum errors of approximately 1.4–1.6% for the dominant stiffness–mode combinations, whereas the integrated formulation limits the corresponding errors to 0.147%. For the cross-ply laminate, integrated prediction errors remain below 0.16% across all investigated cases. The results demonstrate that intact-state sensitivities can provide an accurate reduced-order mapping from prescribed anisotropic stiffness degradation to multimode frequency changes. The formulation does not model fatigue-damage evolution or predict fatigue life, but provides a mechanics-based basis for vibration-informed assessment of fatigue-related stiffness deterioration.