Several waste materials are often used in the mixt-design of asphalt concrete materials to manufacture green construction materials and among them recycled asphalt pavement (RAP) is a favorite material that can be utilized as partial replacement of natural stone aggregates. Addition of such waste and recycled materials may have a negative influence on the mechanical properties and strength or performance of asphalt pavements. In particular, resistance of asphaltic overlays made by some amounts of RAP material against cracking and crack propagation can be reduced and it is necessary to investigate possible effects of RAP addition on cracking resistance of asphalt mixtures. Passage of traffic loads from the cracked overlays and asphaltic pavements can activate all basic tensile and shear mode crack deformations (i.e., pure mode I, pure mode II and pure mode III). In addition, due to the visco-elastic nature of bitumen used in the asphalt mixture, the risk of crack propagation and failure at low temperature conditions is higher than the intermediate and high temperatures. Therefore, in this research, the influence of adding RAP material on the fracture toughness of all three basic fracture modes (namely, KIc, KIIc and KIIIc) is investigated using edge-notched disc bend (ENDB) specimens. Fracture toughness tests are conducted on hot mix asphalt (HMA) mixtures containing 0, 20 and 40 % RAP material (as replacement of natural aggregates) at five low temperatures of 0, -6, -12, -18, -24 oC. Based on the results, all fracture toughness data were decreased by increasing the temperature from -24oC to zero and increasing the RAP content from 0 to 40%. Depending on the test temperature and mixture type (HMA with or without RAP content) the KIc and KIIc values were varied from 0.5 to 1.1 MPa.m0.5. This range for KIIIc value was in the lower limit of 0.35 MPa.m0.5 and 0.75 MPa.m0.5. Some fracture indexes such as fracture toughness ratios (KIIc/KIc, KIIIc/KIc, KIIc/KIIIc, and Kopening/Kshearing-eff) and effective fracture toughness were determined and discussed for the investigated HMA mixtures at different temperatures.
Natural fiber reinforced composites (NFRCs) have gained recognition as sustainable and environmentally friendly alternatives to synthetic composites. However, estimating their fatigue durability remains a major challenge due to their complex and heterogeneous behaviour. This study develops a machine learning framework to predict the fatigue life of hemp fiber-reinforced HDPE composites from experimental data, addressing the specific limitations of conventional empirical models. The dataset is divided into training and testing subsets following a preprocessing phase that includes logarithmic transformation, normalization, and outlier removal. Four regression models are compared: Multiple Linear Regression, Random Forest, Gradient Boosting Regressor, and Support Vector Regression. Grid Search with 5-fold cross-validation is used to optimize hyperparameters and improve predictive accuracy. Model performance is evaluated using the coefficient of determination (R²), Mean Absolute Percentage Error (MAPE), and Root Mean Square Error (RMSE). Results show that ensemble methods, particularly Random Forest (R² = 99.91%, MAPE = 1.11%) and Gradient Boosting (R² = 99.87%, MAPE = 1.52%), substantially outperform linear models and traditional S-N curve fitting. Feature importance analysis reveals that maximum stress accounts for the majority of prediction variance (approximately 68%–81% depending on the dataset), offering actionable insights for material design. The proposed framework demonstrates strong generalization potential and provides a reproducible template for data-driven fatigue modeling in sustainable composite materials.
Fracture toughness is a key engineering design parameter. Fracture of engineering materials and components may occur under 3 basic deformations or modes namely pure mode I (opening), pure mode II (shearing) and pure mode III (tearing). However, in practice the possibility of fracturing under mixed mode I/II, I/III and general mixed mode I/II/III case are more than the pure modes. Several experimental methods and testing specimens have been employed by the fracture mechanics researcher to determine the fracture toughness of engineering materials under different mode mixities. Among them, a recently designed and proposed test configuration named Edge-Notched-Disc-Bend (ENDB) is a suitable and favorite testing method for conducting general mixed-mode I/II/III fracture toughness experiments. In this research following a brief description of the ENDB specimen, a review of some recently published papers for investigating the mixed mode fracture problem is presented. According to such a review, it can be concluded that the ENDB method is a suitable candidate specimen for studying general mixed-mode I/II/III fracture problems in materials with brittle or quasi-brittle nature.
Rapid advances in 3D printing enable the automotive sector to shorten the design cycles, improve flexibility and support customised manufacturing, overcoming the limitations of conventional methods. However, direct comparisons of impact performance particularly those employing instrumented techniques to analyse strain–time signals between SLM-produced SS 316L specimens of varying thicknesses and these specific conventional reference materials remain limited, leading to uncertainty regarding the use of Additive Manufacturing (AM) parts in safety-critical applications. This study aims to assess the strength of additive manufacturing Stainless Steel 316L (SS 316L) powder at various specimen thicknesses and to compare it against the conventional SS 304 and Al 6061-T6. To capture the strain signal, a Charpy machine, a data acquisition system and strain gauges were used in the experiment. Specimen preparation followed the ASTM E8 for tensile test and ASTM E23 for the Charpy impact. Charpy specimens with thicknesses 5, 7.5 and 10 mm were fabricated using an Ermaksan Enavision 120 Selective Laser Melting (SLM) 3D printer under controlled parameters. Results show that increase in specimen thicknesses proportionally increase the absorbed energy and the area under the curve. Compared to reference material, SS 304 exhibited highest impact resistance, followed by AM SS 316L and Al 6061-T6. These findings demonstrate that AM materials can closely match the performance of conventional material. Furthermore, optimising SLM parameters and applying post-processing can improve impact toughness.
This research studied the effect of adding dioctyl phthalate (DOP) on the low- velocity impact properties of unsaturated polyester composites (UPR) reinforced with hybrid fibers (glass-hemp fibers). To achieve this objective, DOP was added to unsaturated polyester at percentages of 1%, 3%, 5%, and 7%. Samples were prepared reinforced with five layers of random glass fibers and two hemp layers (top and bottom). These samples were then subjected to repeated impact testing three times using a drop ball apparatus. The initial impact tests showed that adding DOP up to 5% improved impact resistance, while increasing the added percentage led to an increase in deformation values. Repeated impact tests (first, second, and third) revealed that all samples remained intact but exhibited varying deformation values. The sample containing 5% DOP showed the lowest deformation percentage at 25.17%. A strong correlation was also observed between the rebound coefficient and the added DOP percentage.
