Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Mechanical Evaluation of Recycled PETG Filament for 3D Printing
Full text linkAdditive manufacturing (AM) is revolutionizing various industries by enabling the creation of complex structures with minimal waste. In the context of a circular economy, the importance of recycling cannot be overstated, as it plays a crucial role in reducing environmental impact and conserving resources. This study investigates the mechanical behavior of PETG in the context of recycling for 3D printing applications. With plastic waste posing significant environmental challenges, the pursuit of sustainable solutions is paramount. PETG has emerged as a promising material in additive manufacturing due to its favorable properties, but its sustainability remains a concern. Through mechanical testing, including tensile, compression, and impact tests, PETG specimens are evaluated after one cycle of recycling and reutilization
Effect of Internal Technological Defects and Loading Waveform on Structural Composite Fatigue Life
Full text linkThis paper explores the effect of internal technological defects on the fatigue life of carbon fiber reinforced plastic (CFRP) under simple loading waveforms. One conducted experiments on CFRP specimens with embedded artificial defects, including delamination’s (circular dry-spot) and wrinkling. Following quasi-static tests, one developed a fatigue testing program using triangular and sine waveforms. The findings indicate that these simple waveforms do not significantly affect the fatigue resistance of defect-free CFRP or CFRP with internal technological defects. The presence of the wrinkling defect significantly diminishes the fatigue resistance of CFRP. However, constructing fatigue life curves in relative terms reveals that the reduction in fatigue properties is directly related to a decrease in strength properties. In the case of delamination (dry-spot) defects, a reduction in fatigue life by approximately 2.5 times was observed across the tested range
Numerical study of delamination process of the CFRP composite
Full text linkA quasi-static approach for an interface damage model, incorporating Rayleigh damping for viscoelastic carbon fiber reinforced polymer composites, is introduced. The interface traction-relative displacement behavior is modeled using a thin adhesive layer, similar to cohesive zone models. The problem is solved numerically with a semi-implicit time-stepping method. The cohesive interface model, integrated into the Finite Element Method, was applied to determine the critical force away from the crack tip. Results showed that the numerical delamination under mode I conditions aligned well with experimental data for the cohesive zone formulations studied. The numerical example demonstrates the effectiveness of the proposed model
Residual stresses caused by static and dynamic contact interaction of composite plate and steel spherical indenter
Full text linkA new approach has been developed and implemented to determine the main components of residual stresses that arise as a result of the contact interaction of a spherical indenter and a flat surface of composite plate made. The experimental technique includes drilling a probe hole and measuring the increments of the diameters of this hole in the direction of the principal residual deformations by speckle interferometry. The high-quality interference fringe patterns essential for the implementation of this procedure are visualized both inside and outside the contact dimple. Data from interference measurements of in-plane displacement components are used to determine the principal components of residual stresses based on the unequivocally solution to the properly posed inverse problem. This procedure provides minimal possible errors inherent in a determination of residual stress components by measurements of local deformation response to small hole drilling in orthotropic plate. The presented studies were carried out both for static and dynamic application of contact indentation of a spherical indenter into a flat surface of samples made of laminated carbon fiber material with cross-ply stacking sequence. It is shown that the values of residual stresses, unlike indirect parameters, are a parameter that can be used to establish a correlation between the results of residual strength tests and the quantitative characteristics of the residual stress field in the vicinity of the contact dimple
Mechanical testing of miniature carbon fiber reinforced polymer (CFRP) samples under digital light microscopy
Full text linkThe rapid development of inhomogeneous and anisotropic materials like carbon fiber reinforced polymers (CFRP) with epoxy matrices necessitates a multidisciplinary approach for safe use. This approach should integrate computational modeling and experimental testing across various scales, such as microscopic (<1 mm³), miniature (<10 mm³), and larger engineering samples. Mechanical testing machines must be specifically designed and optimized for each scale, combined with microscopy to observe the response under tension, bending, and compression. This setup enables real-time imaging of defect and crack initiation. Key challenges in miniature sample testing include microscope stage limitations, focusing geometry, force and displacement resolution, and fast data acquisition. The study reported here presents the customization of a 1 kN universal testing machine for in situ testing of miniature CFRP samples in combination with digital light microscopy. The observations made in the course of the present study provide valuable insight into the practical realization of miniature sample mechanical testing. Of particular note is the strain mapping capability across the sample surface afforded by the use of Digital Image Correlation
An investigation of cracks caused by concrete shrinkage and temperature difference in common reinforced concrete bridge structures.
Full text linkThis research investigates cracking in Reinforced Concrete Structures (RCS), particularly in bridge abutments, box girders, and culverts. Cracks often appear even after the concrete has reached its full strength. The current American Bridge Design Standard (AASHTO) permits cracks but doesn’t specify quantitative limits on crack widths. This study uses the fib MODEL CODE 2010 (fib) to analyze RCS under shrinkage and temperature loading. It was found that cracks often exceed fib’s allowable limits, primarily due to significant temperature differences between concrete and steel reinforcement. This is especially prevalent in larger structures with high hydration heat. The use of smaller diameter reinforcement can significantly reduce crack width compared to larger ones, given the same steel ratio. However, a high steel ratio, while reducing crack width, increases susceptibility to cracking. Cracks typically occur after several weeks to months, with widths ranging from 0.30 to 0.70 millimeters due to shrinkage and temperature differences. These findings underscore the importance of considering both shrinkage and temperature differences in the design and maintenance of RCS. By understanding the impact of these factors, as well as the role of reinforcement diameter and steel ratio, engineers can develop more effective strategies for managing and mitigating cracking
Effect of fiber orientation-based composite lamina on mitigation of stress intensity factor for a repaired plate: a finite element study: Repair of thin-walled structures
No full textThe bonded composite repair has proven to be an effective method for addressing crack damage propagation. Numerous studies have employed experimental and simulation techniques to demonstrate the repair performance through the composites. These studies have explored various parameters related to bonded composites, such as size and properties, to enhance repair effectiveness. However, one aspect that has not been thoroughly investigated is the impact of fiber orientation within the composites. Therefore, the current work investigates the effect of the fiber direction of the composite patch bonded on a thin plate under plane stress conditions. Three types of fiber orientation of composite patch have been considered. In this investigation, the finite element method was used to determine the stress intensity factor using the ANSYS commercial code. The research findings showed that the fiber direction influenced the mitigation of stress intensity factor. This study is particularly important for designing the composite patch based on the fiber direction.  
Impact of hybrid nanoparticle reinforcements on Mechanical properties of Epoxy-Polylactic Acid (PLA) Composites: Impact of hybrid nanoparticle reinforcements on Mechanical properties of Epoxy-Polylactic Acid (PLA) Composites
No full textThis study examines the influence of graphene nanoplatelets (GNPs) and multi-walled carbon nanotubes (MWCNTs) on the mechanical properties of SiO2-loaded epoxy-polylactic acid (PLA) composites. Epoxy and PLA were mixed to form the matrix with fillers, including SiO2, GNPs, and MWCNTs. The nanocomposites were prepared with a hybrid filler combination (SiO2/GNPs and SiO2/MWCNTs) with filler concentrations ranging from 0.1 – 0.4 wt. %. The composites were prepared using a combination of bath sonication and hand-casting techniques. They are characterized using tensile, bending impact, and fracture tests. The observed characteristics of GNP/SiO2 and MWCNTs/SiO2-loaded nanocomposites exhibited significant differences. Compared to the unmodified epoxy-PLA composite, incorporating 0.1 wt% of GNP/SiO2 filler improved tensile flexural and impact strength. Conversely, adding 0.4 wt% of MWCNTs/SiO2 filler enhances tensile, flexural, and impact strength. The dispersion mechanism of nanofillers was investigated using Scanning Electron Microscopy (SEM) on fracture surfaces obtained from tensile tests. An ANSYS workbench was used to simulate the impact of filler concentration on nanocomposites' tensile and bending strength, and a numerical analysis was performed
Optimization of clamshell content for improved properties in bamboo-epoxy composites
Full text linkThe present study aims to develop a novel hybrid composite by incorporating clamshell as a secondary reinforcing filler into a bamboo-epoxy composite. The primary objective of this hybridization is to optimize the synergistic benefits of each component, harnessing the strength of bamboo fibres, the durability of epoxy, and the cost-effective repurposing of the waste clamshell. Compression moulding was employed to develop composites with varying filler content (0- 9 wt%). The effect of filler on the physical and mechanical properties of bamboo-epoxy composites was evaluated by conducting tests as per ASTM standards. Experimental results show that the addition of clamshell filler significantly improved composites' properties, but there was a limitation to the addition. Hardness, tensile, and flexural properties were increased, whereas impact strength was reduced. Composites with 6 wt% clamshell exhibited optimum properties, enhancing tensile strength by 20.5% and flexural strength by 24.4 % compared to composites without filler. SEM analysis of fractured tensile and bending specimens revealed an enhanced fibre-matrix bonding with the inclusion of filler and supported the experimental results obtained. The outcome of this study contributes to sustainable development by using natural resources like bamboo fibre and repurposing seashell waste to create cost-effective composite material with enhanced properties
Self-similarity of damage-failure transition and the power laws of fatigue crack advance
Full text linkWe propose the interpretation of the Finite Fracture Mechanics based on the criticality of damage-failure transition due to specific metastability of free energy release. Multiscale mechanisms of fatigue damage-failure transitions in metals are studied for Very High Cycle Fatigue and analyzed as duality of inherently linked two types of singularities related to the collective modes of defects and singularity of stress field as the classical framework of fracture mechanics. Development of collective modes of defects (solitary waves of plastic strain localization and blow-up dissipative structures of damage localization) with the nature of intermediate self-similar solutions are considered for the interpretation of the incomplete self-similarity and mechanism of small crack nucleation (“fish-eye” area in VHCF) and growth up to the Paris crack size. Spatial structural scales corresponding to different stages of damage-failure transition were identified due to the analysis of roughness correlation and estimating of the power (the Hurst) exponent and corresponding structural lengths of characteristic fracture surface areas These lengths and power exponents were used in the constitutive laws as the structure sensitive parameters for characteristic damage-failure transition stages (small crack initiation and growth, the Paris crack advance)