Research & Academic Thesis
Investigating continuous spatial gradation laws, finite element formulations, coupled thermo-structural simulations, and multi-objective optimization algorithms for next-generation Functionally Graded Material (FGM) mechanical components.
Multi-Objective Optimization of Connecting Rods: A Coupled Thermal-Structural Approach
Supervised by Prof. Dr. Md. Afsar Ali, Department of Mechanical Engineering, Bangladesh University of Engineering and Technology (BUET).
Problem Formulation & Engineering Challenge
Internal combustion engine connecting rods operate under extreme cyclic thermo-mechanical environments, experiencing peak compressive combustion pressures exceeding 15 MPa alongside high inertial tension during exhaust strokes. Conventional monolithic steel connecting rods introduce excessive reciprocating mass, degrading fuel economy and elevating bearing loads. Conversely, lightweight aluminum alloys suffer thermal softening and fatigue degradation at the big-end bearing journal.
To resolve this fundamental engineering dilemma, this research investigated an advanced bimaterial and functionally graded architecture applied to an industrial heavy-duty Wärtsilä 20 engine connecting rod geometry.
Key Engineering Highlights
- Geometry: Full-scale Wärtsilä 20 marine/stationary diesel engine connecting rod modeled parametrically in SolidWorks.
- FEA Discretization: Over 82,500 nodes and 29,500 higher-order 3D solid elements in ANSYS Workbench with localized curvature mesh refinement.
- Boundary Conditions: Coupled steady-state thermal distribution ($T = 280^\circ\text{C}$ piston pin, $T = 90^\circ\text{C}$ crank pin) superimposed with peak gas compressive force ($F = 180\text{ kN}$).
- Multi-Objective SSE Optimization: Sum of Squared Errors normalization evaluated across 45 material configurations encompassing AISI 4340 Steel, Al 7075-T6, and Ti-6Al-4V.
Validated Results
Quantitative achievements comparing optimal FGM transition architecture against the baseline monolithic AISI 4340 structural steel:
5 Spatial Volume-Fraction Gradation Laws
Comparative formulation across the 8.85 mm transition layer connecting the Aluminum 7075-T6 shank to Structural Steel ends.
Continuously modulates phase transition across thickness $h=8.85\text{ mm}$ via gradation exponent $\beta \in [0.2, 2.0]$. Effectively eliminates interfacial shear stress concentrations and prevents delamination under cyclic combustion loads.
Constant property gradient across the interface. Offers straightforward manufacturing feasibility via additive manufacturing powder deposition, though exhibiting slight derivative discontinuity at the boundaries.
Features zero first-derivative at both joining boundaries $x=0$ and $x=h$, ensuring seamless elastic modulus continuity and minimizing interfacial shear jump across the Al/Steel boundary.
Smooth, infinite differentiability ($C^\infty$) across the transition zone. Smoothly attenuates thermal expansion mismatch $\Delta \alpha \cdot \Delta T$ and suppresses thermal residual stresses.
Prioritizes rapid mechanical impedance matching near the steel boundary while tapering smoothly toward the aluminum shank core, tailoring stress distribution for high-frequency dynamic response.
Mean-field micromechanical homogenization theory accounting for elastic inclusion interaction, yielding significantly greater predictive accuracy than the classical Voigt-Reuss Rule of Mixtures for high inclusion fractions.
10 Quantified Structural & Fatigue Metrics
Comparative output metrics extracted from ANSYS Workbench finite element simulations across candidate architectures.
| Performance Metric | Monolithic Steel (Baseline) | Abrupt Bimaterial Joint | Optimized FGM Transition | Evaluation Benefit |
|---|---|---|---|---|
| 1. Equivalent von Mises Stress | 490.76 MPa | 542.10 MPa (Stress Spike) | 429.97 MPa | -12.39% Relief |
| 2. Maximum Principal Stress (σ₁) | 512.40 MPa | 585.30 MPa (Singularity) | 448.60 MPa | -12.45% Relief |
| 3. Interfacial Shear Stress (τ) | N/A (Homogeneous) | 34.20 MPa | 8.70 MPa | -74.56% Shear Cut |
| 4. Static Factor of Safety (SF) | 1.21 | 1.09 (Failure Hazard) | 1.39 | +14.88% Boost |
| 5. Geometric Fillet SF (Max Zone) | 4.61 | 4.20 | 5.29 | +14.75% Gain |
| 6. Total Structural Mass | 48.42 kg | 47.10 kg | 46.57 kg | -3.82% Reciprocating |
| 7. Total Elastic Strain | 0.00248 mm/mm | 0.00315 mm/mm | 0.00221 mm/mm | Smoothed Compliance |
| 8. Total Strain Energy | 18.42 mJ | 24.80 mJ (Energy Trap) | 16.90 mJ | Uniform Dissipation |
| 9. Minimum Fatigue Life | 1.0 × 10⁶ cycles | 4.8 × 10⁵ cycles (Severely Degraded) | > 1.0 × 10⁷ cycles | Infinite Life Regime |
| 10. Biaxiality Ratio & Damage | 0.18 (Uniaxial Dominant) | 0.48 (Multi-axial Fatigue Hazard) | 0.12 | Mitigated Shear Multiaxiality |
Scholarly Manuscripts & Preprints
Academic manuscripts submitted and under preparation for peer-reviewed international journals.
Multi-Objective Structural and Material Optimization of Bimaterial Mechanical Components
Details the coupled thermo-mechanical finite element formulations, interfacial shear stress evaluations across bimaterial boundaries, and the Sum of Squared Errors (SSE) multi-objective algorithmic framework for lightweight connecting rod design.
State-of-the-Art in Functionally Graded Material Gradation Laws and Computational Optimization
Extensive synthesis of continuous spatial gradation laws, Voigt/Reuss/Mori-Tanaka homogenization schemes, finite element discretization techniques, and multi-objective Pareto evolutionary optimization for structural FGM components.
Interested in Collaborating on Computational Mechanics?
I am actively preparing for graduate research programs (Ph.D. / M.S.) with focus on structural mechanics, FGM systems, and FEA optimization.