Materials degradation is inevitable and can lead to product failure, incurring loss of product integrity, costs, and even loss of life. While the degradation of monolithic materials has been extensively researched, the failure mechanisms of composite materials remain relatively unexplored. This study investigates the influence of storage aging and defect size on the fracture behavior of rubber composites, specifically for tire sidewall applications. By establishing baseline failure characteristics of fresh composites, this research identifies changes in fracture mechanisms and features as degradation progresses.
Carbon black (CB)-reinforced natural rubber/ butadiene rubber (NR/BR) composites were fractured via tensile load according to ASTM D 412. Fractographic analysis revealed consistent fracture initiation at the edge of dog-bone specimens, followed by the formation of distinct fractures, namely smooth zone, hackle marks, and rupture zone. The “cup-and-cone” fracture origin is indicative of localized shear that resulted to yielding and permanent plastic deformation before initiation of crack. Continued application of tensile load increased the concentrated stress at the origin equivalent to the ultimate tensile strength, initiating crack formation. The crack then propagated slowly through the material, creating a smooth region with faint tear lines. As the load increased, the crack propagation accelerated, forming hackle lines. This reduced the cross-sectional area of the material that could still carry the load, causing the bulk stress to approach its ultimate tensile strength and forming the rupture zone to complete the fracture. The measured ultimate tensile strength and fracture energy of the composites were 15.77 ± 0.58 MPa and 61.08 ± 6.47 J/mm3, respectively.
Exposure to ambient conditions (20-28°C, 55-90% RH) for up to three years significantly degraded the fracture strength of the composites by 37%. While fractographic features remained similar, the fracture origin shifted away from the edge or surface. This suggests that environmental aging, likely due to oxidation brought about by oxygen diffusion from surrounding environment, induced chain scission and crosslink rupture which are typical consequences of oxidation of polymers. Consequently, structural defects formed, acting as nucleation sites for crack initiation. Reduced crosslink density further compromised the material's resistance to crack propagation, leading to premature failure compared to unaged samples.
Considering that defects formed during aging, the influence of defect size on failure mechanisms of notched rubber composites subjected to Mode-I tearing. Compared to unnotched samples, tear lines at the previously identified smooth zone became more pronounced, and secondary crack planes developed parallel to the load direction. The E-strain plot, representing the rate of stress change with respect to strain (dσ/dε), was analyzed to assess crack growth resistance. Distinct regions in the plot were identified, namely strain softening (Payne effect), minimum modulus (Emin), stress upturn, modulus plateau (Eplateau), and fracture. The introduction of a 1mm-notch resulted in the reduction of strain of the Eplateau leading to faster occurrence of fracture as compared to unnotched specimens. At 3mm-notch, fracture occurred after stress upturn whereas immediate fracture occurred at Emin with 5mm-notch. With increasing defect size, the stress concentration at the crack tip also increases such that the strain stiffening contributed by the crosslinks and rubber chains could no longer resist the crack propagation and eventual fracture. Consequently, tearing energy decreased with increasing notch size, from a critical value of 0.239 ± 0.058 J/mm2 for a 3mm notch. Moreover, aging reduced tearing energy up to 73% after two years, highlighting the material's decreased resistance to fracture under both tensile and tearing loads.
This research concludes that environmental aging significantly deteriorates the mechanical properties and fracture resistance of rubber composites. While the overall fracture features remain unchanged, internal defects become more potent in initiating cracks. Future studies should investigate the effects of aging on fracture behavior under dynamic loading conditions and with various filler types and formulations to better understand how aging impacts rubber material performance. This knowledge is crucial for developing more durable rubber components.

The current trend of Horizontal Axis Wind Turbines (HAWT) with respect to energy extraction is towards higher diameter which needs to operate at a wind speed of 15m/s to maximize efficiency. On the other hand, while the Philippines Wind Settings predominantly exhibit 4 m/s, maximum wind speeds is only around 10m/s. Current studies have also showed that extracting energy from these low-level wind speeds is a challenge without utilization of Wind Turbine Augmentation Devices. Relatedly, one of the known wind turbine augmentation techniques is the “shrouding” of HAWT, sometimes called Ducted HAWT. In this regard, a numerical investigation was conducted on the performance of Ducted HAWT using blade design in the study of Alkhabbaz, et al., (2022). The calculations yield average accuracy of 10.83% using Steady-state formulations as opposed to the previous study’s 12.43% that used Transient formulations, a reduction of 1.60%. The CFD calculations were then performed for a Ducted HAWT configuration with the low-reynolds Selig-family Airfoil S7055 as the duct cross-section. It was found out that maximum C_p is 0.4325 at 955 RPM on its design wind speed of 7m/s, an increase of 30.22% from Open Rotor experimental results. Finally, a comparison of Open Rotor HAWT and Inlet-scaled Open Rotor HAWT with the Ducted HAWT was performed. The comparison yielded that Ducted HAWT has an overall superior performance even at low wind speeds with an increase of as high as 44.14% at 4 m/s in TSR = 5 (optimal operational speed). However, thrust levels have been seen to also increase as a high as 30.74% in TSR = 2 at 10 m/s. Generally, the increase in thrust levels is offset by the increase in power generation thereby exhibiting superior performance of Ducted HAWT with minimal aerodynamic tradeoffs.

Green materials, such as lumber , have played a vital role in the construction and furniture industries. However, the supply of lumber cannot meet current global demand. One promising alternative is the development of engineered bamboo products. Raw bamboo culms undergo a series of processes and are glued together to form structural parts. The quality of engineered bamboo products depends on the strength of the adhesive. As the industry moves to use non-toxic adhesives, polyvinyl acetate (PVAc) is considered for bamboo. However, because of the hydrophobic properties of bamboo, the adhesion strength of PVAc is not strong enough. Engineered bamboo is also a cellulosic material, which is considered a combustible material. Due to the drying process, to prevent molds, its fire-retardant properties are lower compared to those of lumber. In this work, the PVAc adhesion strength and fire retardancy were improved by pretreatment of bamboo slats using a custom-built atmospheric pressure plasma jet. Argon (Ar), air, and vaporized hexamethyldisiloxane (HMDSO) were used as the process
gases. The results showed that the single-lap shear test revealed a 33% increase in shear strength compared to untreated bamboo slats. When air was added to the Ar plasma, the shear strength increased to 55%. Further analysis of the plasma-treated surfaces revealed a significant increase in surfacefree energies, especially the polar energy component. This led to an increase in hydrophilicity. The combination of Ar and air plasma treatment induced physical and chemical changes on the surface, which improved the affinity for water-based PVAc. Using vaporized HMDSO, a thin layer of organosilicon is deposited on bamboo surfaces through plasma polymerization. This thin film served as a barrier which increased the ignition time to almost three times that of untreated bamboo. This work demonstrated the use of a simple yet versatile plasma system to tailor the surface properties of bamboo. Plasma treatment to enhance the PVAc adhesion strength and to improve the fire retardancy of bamboo is an emerging technique for the fabrication of bamboo laminates. This will contribute to making the construction and furniture industries more sustainable

The analysis of fluid-structure interactions is a process that involves the coupling between the fluid and structural domains. This study presents a combined Modified Rigid Body-Spring Method (MRBSM) – Smoothed Particle Hydrodynamics (SPH) Model for simulating such interactions. It aims to provide a novel approach to the analysis of FSIs which make use of kinematics of particles and rigid bodies, as opposed to typical finite element schemes. The interdependence between the phases is observed in the transmission of output to one another, instead of compatibility equations, further simplifying the analysis. The model initially calculates fluid particle positions, velocities and accelerations, calculates the equivalent forces, to be applied as external loads to the solid rigid body assembly. The rigid body locations and orientations are calculated. This new orientation of the solid is transmitted to the fluid phase as deformed boundary conditions. This study made use of a validation experiment similar to that by Antoci et al. in 2007. From having 1600 initial particles, it was found that the accuracy of the model was maintained by halving the particle size, while doubling the size caused inaccuracies at the early stages of the simulation. There were noticeable accuracy improvements up to a 5-component model, accuracy loss at 6 components and then instability at 7 components. By error comparison, it was found that the 3-component model was the most reasonable simulation, with relative RMSE = 4.09%, relative peak deviation = 2.56% and relative average deviation = 2.93%. Discrepancies from the expected results and instabilities may be attributed to the artificial introduction of higher modes of vibration brought about by the increase in number of MRBSM discretization components, which can be a promising starting point for further investigation.

The Philippines, located within the biodiverse Coral Triangle, faces significant threats from oil spills. This study focuses on two key regions: the Verde Island Passage (VIP) and the Panay Gulf and Iloilo-Guimaras Strait (PG-IGS), selected due to high historical oil spill volumes and frequencies in these two areas. This research used a stochastic modeling approach using the web-based version of the GNOME model and integrate it into an oil spill risk assessment. The oil spill modeling showed that the simulated oil spill patterns were able to capture the actual oil spill trajectory observed in the available satellite data. The risk assessment identified Batangas Bay and the south-eastern tip of Guimaras Island as the highest-risk areas in the VIP and PG-IGS, respectively, as shown in the generated risk map. This affects four MPAs in the VIP and one in PG-IGS. Different oil spill prevention methods in the two study areas were also determined. While policies for oil spill prevention are already established, their effectiveness relies heavily on proper implementation through enhanced communication among the responsible government agencies and increased number of trained personnel. Additionally, the cost analysis highlights substantial financial and environmental impacts, demonstrating that the total response cost, socio-economic cost, and environmental cost increase proportionally with the volume of the oil spill. Among these costs, the socio-economic impact is the most significant, indicating that the oil spill affects surrounding communities more severely than it does the environment, as reflected in the comparatively lower environmental cost. This highlights the importance of preparedness and reliable response mechanisms in the two study areas.