Nowadays, the number of Distributed Denial of Service (DDoS) attacks is growing rapidly. The aim of these type of attacks is to make the prominent and critical services unavailable for legitimate users. HTTP flooding is one of the most common DDoS attacks and because of its implementation in application layer, it is difficult to detect and prevent by the current defense mechanisms. This attack not only makes the web servers unavailable, but consumes the computational resources of the network equipment and congests communication links. Recently, the advent of Software Defined Networking (SDN) paradigm has enabled the network providers to detect and mitigate application layer DDoS attacks such as HTTP flooding. In this paper, we propose a defense mechanism named HTTPScout which leverages the benefits of SDN together with Machine Learning (ML) techniques to detect and mitigate HTTP flooding attack. HTTPScout is implemented as a security module in RYU controller and monitors the behavior of HTTP traffic flows. Upon detecting a malicious flow, it blocks the source of the attack at the edge switch and preserves the network resources from the adversarial effects of the attack. Simulation results confirm that HTTPScout brings a significant improvement of 64% in bandwidth consumption and 80% in the number of forwarding rules compared to normal SDN.

In recent years, the explosive growth of the Internet has led to an increment in the number of Distributed Denial of Service (DDoS) attacks. HTTP Flooding is a critical DDoS attack that targets HTTP servers to prohibit users from receiving HTTP services. Moreover, it saturates the link bandwidth and consumes network resources. Because the attack is launched at the application layer, it is difficult to defend against it using current countermeasures such as firewall or Intrusion Prevention System (IPS). In this paper, we propose SHFD, which leverages the Software-Defined Networking (SDN) paradigm to mitigate HTTP flooding attacks. We implement SHFD as a defender module on the SDN controller to detect and mitigate the attack in the first place. Experimental results gathered from Mininet confirm that SHFD brings a significant improvement of 13% in detection time and 29% in the number of blocked malicious flows compared to the state-of-the-art approaches.

In recent years, the Underwater Internet of Things (IoUT) has become a popular technology for exploring the underwater environment. IoUT enables administrators to explore and monitor underwater environmental phenomena from anywhere in the world where there is Internet access. Due to the harsh underwater environment, the reliability of communication between sensor nodes deteriorates, causing certain performance issues such as higher packet loss rate and long end-to-end delay. Therefore, it is essential to manage the communications between the sensors to address these problems in order to improve the QoS. Software-defined networking (SDN) is one of the most promising architectures for providing efficient network management by decoupling the data plane from the control plane of the network. This paper proposes a new QoS routing technique for SDN-based IoUT aiming at improving QoS by establishing reliable paths between sensor nodes. To do this, the controller gathers the 3D coordinates of each underwater sensor in order to compute the distance between the nodes. Then, it estimates the reliability of each link by using underwater acoustic equations. Finally, it calculates the most reliable path with minimum delay and installs the path on the nodes located along it. The experimental results show that our mechanism significantly outperforms other non-SDN approaches in terms of several performance measures ranging from packet loss ratio and end-to-end delay to energy consumption.

The present study evaluates the toughening capability of electrospun PA66 nanofibers for carbon/epoxy composite laminates subjected to mode II loading conditions at elevated temperatures. The Dynamic Mechanical Analysis (DMA) test showed that the glass transition temperature of the produced nanofibers is in a range of ∼60–80 °C. Accordingly, End-Notched Flexure (ENF) carbon/epoxy specimens interleaved by a 50 μm-layer of electrospun PA66 nanofibers were subjected to the quasi-static mode II loading at room temperature (∼25 °C), 100 °C, 125 °C, and 160 °C. At room temperature, the mode II interlaminar fracture toughness (G_IIC) of the nano-modified specimen was ∼4 times higher than the virgin specimen (non-modified) (3.12 kJ/m² vs 0.81 kJ/m²). The results showed that G_IIC of the virgin specimen was independent of temperature. However, in the case of the nano-modified specimen, although the G_IIC did not change from room temperature to 100 °C (3.12 kJ/m² vs 3.09 kJ/m²), by further increasing temperature to 125 °C and 160 °C, G_IIC dropped by 34% and 43% respectively (2.05 kJ/m² and 1.77 kJ/m² respectively). 3D surface scans and Scanning Electron Microscopy (SEM) images of the fracture surface revealed three reasons for decreasing the toughening capability of the PA66 nanofibers at high temperatures: a) the crack crosses the nano-layer less at high temperatures, b) the dominant damage mechanism at low temperature is “cohesive failure”, the damage propagation within the nanolayer, while at higher temperatures “adhesive failure”, the debonding of the nanolayer from carbon fibers, plays a critical role in the fracture, and c) severe plastic deformation of nanofibers at high temperatures.

Interleaving composite laminates with nanofibrous mat is one of the most reliable methods for increasing interlaminar fracture toughness. The present study seeks to find out how the damage mechanisms of carbon fiber reinforced polymers (CFRPs), subjected to the mode-I and mode-II fracture tests, are affected while those are modified by interleaved Polyamide 66 (PA66) electrospun layers. For this goal, acoustic emission (AE) and scanning electron microscope (SEM) techniques were used for assessing the damage mechanisms. The mode-I test results showed that adding nanofibers could decrease matrix cracking, fiber breakage, and fiber/matrix debonding by 92%, 27%, and 87%, respectively. The AE demonstrated that no fiber breakage occurred during mode-II loading in both non-modified and nanomodified specimens which was validated by SEM images. On the other hand, the two other damage modes, i.e. matrix cracking and fiber/matrix debonding, decreased about 97% in the nanomodified laminates.

The geometrical features of nanofibers, such as nanomat thickness and the diameter of nanofibers, have a significant influence on the toughening behavior of composite laminates. In this study, carbon/epoxy laminates were interleaved with polysulfone (PSF) nanofibrous mats and the effect of the PSF nanomat thickness on the fracture toughness was considered for the first time. For this goal, the nanofibers were first produced by the electrospinning method. Then, double cantilever beam (DCB) specimens were manufactured, and mode-I fracture tests were conducted. The results showed that enhancing the mat thickness could increase the fracture toughness considerably (to about 87% with the maximum thickness). The toughening mechanism was also considered by presenting a schematic picture. Micrographs were taken using a scanning electron microscope (SEM).

This research focused on fracture and fatigue response of carbon/epoxy laminates modified with electrospun nylon 66 nanofibers. For this purpose, AS4/8552 composite laminates interleaved by nanofibrous mat were considered under mode-I quasi-static and fatigue loading conditions. According to test outcomes, the fracture toughness increased about 133% under quasi-static tests. On the other hand, the plotted fatigue curves showed that the crack growth rate significantly decreased in modified samples and the threshold energy release rate enhanced about 128%. Finally, scanning electron microscopy (SEM) was also conducted to investigate the damage mechanisms.

The advantages of applying electrospun nylon 6,6 as a toughening agent in epoxy-based composite laminates have been considered already under quasi-static mode-I and mode-II fracture loads. In the present study, the fatigue behavior of unidirectional carbon/epoxy laminates interleaved by nylon 6,6 is investigated under mode-II loading. To this aim, a 50-μm nylon 6,6 nanofibrous mat was put between mid-layers of a carbon/epoxy laminate, and then quasi-static and cyclic loadings were applied on End Notched Flexure (ENF) samples to investigate the onset of delamination growth and crack propagation rate (da/dN) under different ratios of G_IIin/G_IIC. The results showed that the mode-II fracture toughness increased about 161% under quasi-static loading tests. Additionally, the fatigue test results proved that the crack propagation was 14–27 times slower in the modified sample (with the same G_IImax) because of the bridging between composite layers caused by nanofibers. Different fractography techniques including optical microscopy, microscopic 3D surface scanning device, and scanning electron microscopy (SEM) were also used to explore further the toughening mechanism.