Defect and Diffusion Forum Vol. 453

Abstract: The stress-strain curves for AL-1050 were experimentally determined through compression tests. The friction factor between the AL-1050 aluminum alloy and the die material was subsequently obtained via ring compression tests, with graphite serving as the lubricant during the LED lamp heat sink forging process. The design of the forging dies for the LED lamp heat sink carefully considered several critical factors, including product geometry, parting line, die fillet radius, shrinkage, and flash. Subsequently, die dimensions, the stress-strain curve, the friction factor, and initial billet dimensions were utilized as input parameters for the finite element analysis (FEA) of the LED lamp heat sink's forging. The FEA successfully predicted the maximum forging load, effective stress distribution, and die-filling behavior of the LED heat sink during the forging process. Following the parameters established by the simulation, an LED lamp heat sink was fabricated using a forging machine. The experimental results showed excellent agreement with the simulation predictions, thereby validating the accuracy of the FEA model in forecasting the forging process.

Abstract: This study utilized a computerized universal testing machine to obtain the stress-strain curves and fracture behavior of AZ31 magnesium alloy at various temperatures. Additionally, friction coefficients were determined through friction tests conducted at these different temperatures. Ductile fracture analysis was performed during the graphite-lubricated hemispherical deep drawing process at various elevated temperatures. By employing finite element simulation combined with ductile fracture criteria, we determined the forming load, punch stroke, and fracture location for AZ31 sheet metal forming at different working temperatures. Finally, the predicted values from the simulation were compared with experimental results obtained during the hemispherical deep drawing process. The simulation results showed good agreement with the experimental values for both the punch stroke and the fracture location during the hemispherical deep drawing process. This consistency confirms the feasibility of the method for predicting ductile fracture during deep drawing at various elevated temperatures.

Abstract: Non-woven fabrics are made of fiber mesh and carded or spun. They have the advantages of low cost, high output, easy production. The manufacturing process has a small carbon footprint and environmental benefits, which is in line with today's environmental issues and the important value of a circular economy. However, non-woven fabrics are thin and not very hard. They are usually assembled with other materials by vibration welding or adhesion, but they often lose their replaceability. This study attempts to develop a nonwoven fabric locking method and explore the impact of different friction stir drilling parameters on the formation of the boss and bushing.

Abstract: The current paper presents a comprehensive fatigue analysis of the steel column shaft spindle in a model CNC machine tool under prototypical cyclic loading conditions. The study integrates multi-body dynamic simulation with RecurDyn and stress-based as well as strain-based fatigue life prediction procedures. The geometry of the shaft, achieved through CAD and meshed as a deformable body using the RFlex interface, was loaded with eight-point force-controlled cyclic loading mimicking operation machining forces. Stress-based analysis made use of Manson-Coffin life criterion along with Gerber and Goodman mean stress correction models, whereas strain-based analysis made use of the Brown-Miller and Morrow criteria along with corresponding mean stress corrections. Material characterization was enabled by developing an S-N curve for the shaft steel, enabling accurate estimation of life. Fatigue damage accumulation was evaluated using Miner's Rule, and damage contour plots to find critical locations. Results indicated maximum damage values of the order 10⁻⁹ for stress-based and 10⁻¹⁰- 10⁻⁸ for strain-based models, which correspond to predicted fatigue lives in excess of 10¹³ cycles under the applied boundary conditions. Gerber and Goodman criteria-based safety factor analysis also provided minimum values of 6.12 and 4.93, respectively, which indicate a substantial margin against fatigue failure. The approach provides an experimentally validated framework for the evaluation of machine tool structural elements' durability, enabling optimal support schemes and longer life of operation.

Abstract: This study presents an integrated rigid flexible dynamic analysis of a CNC machine tool column using the Full Body General Motion Transfer (FBGMT) method and R-Flex flexible body modeling in RecurDyn, validated through comparison with ANSYS finite element modal results. The FBGMT approach simulated the vertical translation of the spindle head driven by a ball screw linear guide system, generating realistic motion data for structural evaluation. The R-Flex model converted the column into a flexible body using an RFI-based contact method, enabling the assessment of deformation, stress, and strain at three distinct tool head positions top, mid, and bottom. Modal analysis was performed in both RecurDyn and ANSYS under matched geometry, mesh density, and boundary conditions to verify frequency and mode shape consistency. Results show that displacement and stress increase as the tool head moves downward, with all responses remaining within elastic limits. Frequency deviation between RecurDyn and ANSYS remained within engineering tolerance, and mode shapes demonstrated strong correlation. This integrated workflow demonstrates a robust methodology for predicting CNC structural performance under realistic motion induced loading.

Abstract: Thermoset and thermoplastic composites are extensively used in aerospace because of their exceptional mechanical properties. Compared to thermoset composites, thermoplastic matrix composites offer excellent chemical and physical damage resistance and are more cost-effective to produce. However, barely visible impact damage (BVID) poses a critical risk to thermoplastic Carbon Fiber Reinforced Polymer (CFRP) aerospace structures due to its limited surface manifestation and significant effect on compressive strength. This study presents a thermographic nondestructive evaluation (TNDE) approach based on Thermographic Signal Reconstruction (TSR) fingerprints to enable repeatable depth and area estimation of impact-induced damage. A data-driven threshold is derived from the logarithmic slope histogram sequence, allowing consistent separation of sound and damaged regions without relying on contrast extrema or operator-dependent frame selection. The method is first validated using flat-bottom holes (FBH) of known geometry and then applied to an industrial thermoplastic composite demonstrator subjected to multiple impact energies. Quantitative comparisons with ultrasonic C-scan measurements demonstrate convincing correlation and stable trends, with error magnitudes consistent with known physical limitations of flash thermography for deeper or structurally constrained defects. The results demonstrate that the proposed methodology offers a resilient, contactless alternative for swift BVID screening and comparative damage quantification in aerospace composite inspection.

Abstract: Grinding rollers are critical components of the cement manufacturing process, with the grinding rollers experiencing heavy mechanical and chemical stresses that can cause early failure. The present research aimed to analyze a failed roller specimen, which included a backing material and an overlay layer, to determine the root causes of deterioration. The research method adopted combined visual examination, Scanning Electron Microscopy (SEM), Energy Dispersive X-ray Spectroscopy (EDS), and X-ray Diffraction (XRD) analysis. Macroscopic investigation determined pitting, cracking, heavy corrosion, and wear patterns on the overlay material. Investigations by SEM/EDS found significant concentrations of chlorine (Cl) and sulfur (S) within the damaged interface and within fissures, consequently proving their roles as potent corrosive agents. Moreover, oxygen (O) was detected in substantial amounts, advocating massive oxidation processes. The results of the XRD examination of the corroded area revealed products of corrosion that correspond to oxide and chloride phases. The results demonstrate that grinding roller failure results from a combined effect of mechanical fatigue and chemical corrosion, with specific vulnerability being evident in the overlay layer. The outcome emphasizes the need for better material selection, optimal overlays deposition, and the utilization of protection treatments to enhance the service life of grinding rollers within the cement manufacturing industry.

Abstract: The vacancy-carbon interactions control defect kinetics and the properties of ferritic iron. Here we use spin‑polarized density‑functional theory on 3×3×3 bcc‑Fe supercells with one to four carbon atoms in octahedral interstitial sites to quantify how carbon modifies vacancy energetics. Two limiting families are considered: dilute configurations with C far from the vacancy and compact VCₙ clusters (n=1-4) with C placed in the nearest octahedral shell. For the dilute case, the vacancy formation energy remains close to that of pure Fe. In contrast, for compact clusters the effective formation energy of a vacancy bound to carbon, E_{f_VC}, decreases markedly with increasing n, while the total binding energy increases and then saturates. The incremental stabilization E_add stays positive up to n = 3 and turns negative for n=4. E_trap is small and positive for n=1-2, but becomes negative for n ≥ 3, consistent with carbon‑rich microenvironments biasing vacancies into VCₙ states. Increasing n moderately reduces N(E_F), particularly in the minority-spin channel, which is consistent with strengthened Fe-C hybridization and the larger binding energies of the VC_n complexes. Finally, using a Seydel thermodynamic trapping model parameterized by our ab initio E_bind (VC_n) we predict effective vacancy diffusivities D_{v_eff}(T,C_tot) that exhibit trends in line with prior analyses, while reflecting the stronger trapping implied by our energetics. Consistent with our DOS analysis, increasing carbon content strengthens Fe-C hybridisation, shifts Fe d states to lower energies and reduces N(E_F), indicating a gradual transition from metallic Fe-Fe bonding to a more covalent Fe-C bond character. This work closes an important gap between electronic-structure data and mesoscale modelling by providing a consistent set of vacancy-carbon energetics and effective vacancy diffusivities for dilute C in α-Fe, which serves as a model system for ferritic Fe-based alloys.

Abstract: This study examines the influence of nickel (Ni) additions on the microstructure and hardness of Ductile Iron (DI) produced in permanent molds, where higher cooling rates significantly affect solidification behavior. Ductile iron melts were prepared in a 100-kg induction furnace with varying Ni levels (0.06–12.30 wt.%), and Y-block castings were produced in accordance with ASTM A536. Optical microscopy and image analysis were employed to evaluate graphite morphology and matrix phases, while color etching was used to differentiate bainite and martensite. Results show that increasing Ni reduced the nodule count but promoted the formation of primary graphite due to hypereutectic solidification. The matrix evolved sequentially from ferrite to pearlite, and then to bainite and martensite with higher Ni content. At Ni levels above 9–12 wt.%, retained austenite was observed. Hardness increased with Ni additions up to ~10 wt.% but decreased slightly at higher contents due to the presence of retained austenite. These findings demonstrate that controlled Ni additions can produce ductile iron with comparable hardness to the Austempered Ductile Iron (ADI) without heat treatment.