Italian Group Fracture (IGF): E-Journals / Gruppo Italiano Frattura
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Influence of contact interaction character on residual stresses arising over damaged area in composite plate
Full text linkNew data concerning the values of residual stresses that arise as a result of the contact interaction of a spherical indenter and a flat surface of composite plate have been obtained. The studies are performed for both static indentation and impact influence of a spherical indenter into a flat surface of coupons made of carbon fibre reinforced polymer with cross-ply stacking sequence. The high-quality interference fringe patterns, generated by through hole drilling in contact interaction zone, which are essential for residual stress deriving are visualized and quantitatively processed both inside and outside the contact dimple. The distributions of residual stresses obtained during static and impact contact interaction, which leads to the appearance of dimples of almost the same diameter, are compared. A comparison of the values of the principal residual stress components corresponding to the contact interaction of similar composite plates with a spherical impactor of different diameters for the same impact energy is presented. Several factors have been identified that relate the decrease in the residual strength of damaged specimens to the values of the residual stress components. Evaluation of the influence of coupon’s thickness as well as an impact energy level on the residual stress values inherent in the vicinity of contact dimple is presented
Damage of additively manufactured polymer materials: experimental and probabilistic analysis
Full text linkThis paper presents a study on the tensile, fracture, damage, and reliability properties of 3D printed polylactic acid (PLA), based on a series of experiments. The study focuses on polylactic acid (PLA) samples produced using fused filament manufacturing (FFF) technology, specifically examining unidirectional print orientations of 0°, 45°, and 90°. Tensile testing demonstrated significant anisotropy in mechanical behavior, The specimens oriented at 0° exhibited the highest tensile strength, while those at 90° showed the lowest. An increase in artificial crack length (a) resulted in a progressive decrease in the mechanical properties. Weibull analysis confirmed the presence of significant anisotropic behavior in 3D-printed PLA specimens, with ultimate stress (σu0) values ranging from 39.82 MPa for the 90° orientation to 44.69 MPa for the 0° orientation, and elastic stress (σe0) values from 35.49 MPa (90°) to 39.11 MPa (0°), indicating greater strength for the 0° oriented specimens. Damage evolution analysis showed accelerated damage, with the 90° orientation demonstrating the fastest rate of damage compared to the 0° and 45° orientations. This indicates that the 90° orientation is more vulnerable to crack propagation and has diminished structural integrity under stress
Integral bridge abutment with composite dowels: structural scheme and failure patterns
Full text linkThis paper presents a novel integral abutment design incorporating a composite dowel girder and H-shaped steel pile abutments to enhance load-bearing capacity and construction efficiency. Numerical analysis is conducted to investigate the failure modes, load-transfer mechanisms, and ultimate bearing capacity of the integrated abutment joint. A parametric study examines the influence of key factors, including steel girder web thickness and the reinforcement ratio of the deck and abutment, on structural performance. Results indicate that abutment failure is primarily attributed to concrete compression failure beneath the steel girder. Based on the findings, a formula for predicting the ultimate bearing capacity of the integrated abutment joint is proposed. Under the same steel girder depth and bottom plate width, the steel consumption of the integral abutment proposed in this work is reduced while the section has a slightly higher bearing capacity compared that of the traditional I-shaped steel girder
Experimental Investigation of Tensile and Bond Strength for a GFRP–SSWM Hybrid Wraps
Full text linkThis study experimentally investigates the tensile and bond performance of novel GFRP–SSWM hybrid wraps developed using two epoxy adhesives - Sikadur 30 LP and Sikadur 330. A total of 42 coupon specimens for tensile testing and 48 dumbbell specimens for bond testing are prepared using various two-layer and three-layer configurations of GFRP, SSWM, and their hybrids. Tensile tests are conducted as per ASTM D3039, and specimen performance are evaluated in terms of ultimate load capacity, displacement at peak load, stiffness, rupture strain, and failure modes. Fractographic assessment is also performed at the failure plane of coupon specimens. Study results of tensile and bond test, indicate that GFRP-only specimens exhibit high tensile strength and stiffness but fail in a brittle manner, while SSWM-only specimens show greater ductility with reduced strength. Hybrid configurations offer a balanced response between strength and ductility. Among hybrids, GS specimens bonded with Sikadur 30 LP show superior performance in two-layer systems. Fractographic observations confirm effective hybrid action between GFRP and SSWM without delamination or layer separation at the interface. The capacity utilization ratio further supports that Sikadur 30 LP performs better than Sikadur 330, especially in hybrid configurations involving SSWM. The study highlights the mechanical viability of GFRP-SSWM hybrid wraps for use in strengthening applications
Very High Cycle Fatigue (VHCF) of notched specimens: a review
Full text linkA large number of mechanical components are subjected to fatigue loading beyond 106 cycles. The VHCF behaviour of smooth specimens has been extensively investigated in the recent years, even if more efforts are necessary to reveal the mecahnism governing failures. On the other hand, the influence of notches in the VHCF regime remains relatively unexplored. In the present review, the available studies on the VHCF behaviour of notched components have been analysed and compared.
The review highlights that multiple approaches for accounting for the stress concentration introduced by notches are available in the literature and that notches alter the failure mechanisms compared to smooth specimens. In general, a model for the design of complex structures against VHCF failures and with notches/geometric discontinuities is missing, and more experimental data for different materials are to be obtained to prove the validity of the approaches already available in the literature or employed for the High Cycle Fatigue (HCF) life range. Moreover, since the ultrasonic fatigue testing machines are mainly used for the tests, different definitions for the stress concentration factors have been found in the literature, since, with these types of tests, the stress distribution within the specimen depends on the wave propagation and on the resonance condition
Improved flexural behaviour of reinforced concrete beam strengthened using stainless steel wire mesh
Full text linkThe paper presents an experimental investigation of the flexural behaviour of reinforced concrete (RC) beam elements strengthened externally with stainless steel wire mesh (SSWM). SSWM has the potential to be an alternative composite material in place of Carbon Fiber Reinforced Polymer (CFRP) and Glass Fiber Reinforced Polymer (GFRP) because of advantages such as being cost-effective, having more fire-resistance and corrosion resistance, good bond behaviour with concrete, improve the strength of members, leaving minimal effects on structural aesthetics as it has less thickness and ease in availability. In the present study, SSWM has been wrapped externally over the beams having three different wrapping patterns, including fully wrapped vertical SSWM strips over the beam, partial wrapping of vertical SSWM strips in between the stirrups of the beam and partial wrapping of vertical SSWM strips above the stirrups of the beam, and control beam with no wrapping, each configuration having two test specimens. Results of experimental investigation in terms of cracking load, ultimate load, corresponding deflection, ductility, initial stiffness and energy absorption capacity of different wrapping patterns have been obtained and compared with those of control beam specimens. From the results obtained, it has been demonstrated that the fully wrapped SSWM strip wrapping pattern enhanced the flexural strength of the beam and showed the highest strength gain compared to the other wrapping patterns
Effect of pearlite nanoclay reinforcements on the mechanical and tribological behaviour of AA7076 metal nanocomposites
No full textAluminium alloy composites are extensively utilised in the aerospace, automobile, and marine industries due to their lightweight structure and high strength-to-density ratio. However, there remains significant potential to further improve these composites for advanced applications by enhancing their strength-to-weight ratio, corrosion resistance, wear resistance, and temperature performance. This study investigates the mechanical and tribological properties of AA7076 alloy reinforced with varying concentrations (1.0 and 1.5 wt.%) of perlite nanoclay. These composites were synthesized using a motorised stir casting process and characterised through tensile, wear, and hardness tests. Results showed that 1.5 wt. % perlite nanoclay composite exhibited the most significant improvements, with hardness, tensile strength, and wear resistance increasing by 32%, 38%, and 59%, respectively, compared to the base AA7076 alloy. Finite element simulations in ANSYS Workbench predicted tensile strengths in close agreement (within 5 – 8%) with experimental results, validating the strengthening effects of nanoclay. The enhancements are attributed to the homogeneous dispersion of nanoclay particles, strong interfacial bonding, and their role in restricting dislocation motion. These findings establish perlite nanoclay as a cost-effective and sustainable reinforcement for aluminium alloy, well-suited for demanding applications in automotive, aerospace, and marine industries, offering a promising combination of lightweight design and superior performance
Study on mechanical, wear, corrosion and fracture characteristics of Al7075 by modifying nano sized Magnesium (n-Mg) element
Full text linkAluminum alloys are widely used in the automobile industry because of their excellent mechanical strength, low weight, and remarkable resistance to corrosion and wear. The purpose of this study is to investigate how the microstructure, mechanical properties, and corrosion resistance of the Al7075 alloy are affected by the addition of nano sized magnesium (n-Mg) particulates. Stir casting was used to fabricate the alloy samples, which had varied wt. % of n-Mg (0, 1, 1.5, 2, and 2.5 wt. %). By studying corrosion, wear, microstructural, and mechanical characteristics, the impact of n-Mg dispersion was assessed. The findings provided crucial information on magnesium's function in fortifying aluminum by demonstrating that optical micrographs depicted a homogeneous distribution of n-Mg particles within the Al7075 matrix. Magnesium at the nanoscale improved the alloy's strength, reduced dislocation motion, and refined the grain structure. However, as evidenced by a decrease in impact energy, the addition of magnesium also resulted in decreased toughness and ductility. Tensile strength, hardness, wear resistance, as well as corrosion resistance all improved by roughly 9.21%, 15.73%, 18.82%, and 23.80%, respectively, in the modified Al7075 alloy
Fatigue experimental characterisation of brazed joints in aluminium microchannel heat exchangers
Full text linkBrazing is a widely employed joining technique for aluminium components due to its cost-effectiveness and compatibility with complex geometries. However, the structural integrity of brazed joints under cyclic loading remains a scarcely addressed scientific and engineering concern. This study investigates the tensile and fatigue behaviour of aluminium 3xxx-series alloy components employed in microchannel heat exchangers—headers and multi-port extruded tubes—both in the as-received and heat-treated (brazing cycle) conditions. Tensile tests were performed on parent materials using a microtensile equipped with a Digital Image Correlation (DIC) system for accurate strain evaluation during testing. On the other hand, uniaxial fatigue tests were performed on specimens containing a representative brazed joint. Finite element analyses were used to design the fatigue specimen geometry based on stress concentrations observed in simplified heat exchanger models. Fatigue test data were employed to determine fatigue behaviour both in the finite life region of high-cycle fatigue and to characterise the fatigue endurance limit at 107 cycles. Experimental testing unveiled crack initiation consistently occurring at the brazed fillet toe near the tube lateral edge. SEM observations revealed surface-initiated cracking, ratchet marks, sub-surface inclusions and final ductile failure. Results underline the need for fatigue-based design criteria for brazed aluminium structures
Evolution of prototyping in automotive engineering: a Comprehensive Study on the reliability of Additive Manufacturing for advanced powertrain components
Full text linkAdditive manufacturing (AM) could be used to reduce the production times of prototypes; however, further research is required to address metals structural parts. To obtain the correct properties, some relevant factors to be considered are the build volume, shape factor, and the need for specific heat treatments. This study aims to evaluate the reliability of AM prototypes applied at a new powertrain system developed to reduce vehicle emissions. Firstly, it was investigated the mechanical behavior, microstructure, and the effect of sample size and heat treatments on both specimens and prototypes made of AM 17-4PH steel. Finite Element Analysis (FEA) was performed to evaluate the structural resistance. Finally, the prototypes were produced, analyzed, and tested on a functional engine test bench to evaluate their reliability. The mechanical properties decreased with an increase in the sample volume. After heat treatment, the yield strength increased, due to the transformation of δ-ferrite in martensite and the reduction of retained austenite. The engine test bench was successfully completed. The conclusions set the basis for similar future applications of time-effective prototypes that can be dimensioned owing to appositely developed postprocesses that guarantee the required resistance