Influence of Post Weld Heat Treatment on the HAZ of Low Alloy Steel Weldments

The heterogeneous nature of weldments demands an additional processing to retain and/or improve the joint properties. Heat Affected Zone, the zone Adjacent to the weld metal zone is critically affected by the sudden dissipation of heat from weld metal during welding. Toughness of this zone becomes weak as the grains get coarsened and the interface between the two regions is more prone to fracture. Post weld heat treatment is thus generally carried out on the weldments to relive the thermal residual stresses and to enhance the properties of welded joints. This paper discusses about the influence of post weld heat treatment on the fracture toughness of low alloy steel weldments. Fracture toughness of heat treated weldments was determined using standard CTOD test and the results were correlated

Study on Blast Pressure Resistance of Foamed Concrete Material

Great demand exist for more efficient design to protect personals and critical components against explosion or blast wave, generated both accidentally and deliberately, in various blast scenarios in both civilian and military activities. Concrete is a common material used in protective design of structures. Recently, the demands on producing the lighter concrete material have become interest in concrete research. Foamed concrete is a possible alternative of lightweight concrete for producing intermediate strength capabilities with excellent thermal insulation, freeze-thaw resistance, high-impact resistance and good shock absorption. This paper explores the role and development of Blast Pressure Resistant Materials (BPRM’s) on foamed concrete. The explosive tests were conducted to determine the blast mitigating properties. The results show that when the foamed concrete density is increases the blast energy absorption capability will be decreases due to reduce of cavity volume. This is suggested that cavity plays an important role to dissipate and absorb the shock energy of the blast

Finite Element Simulation on Crack Analysis of a Thick-Tube

Most engineering failure began with cracks. Crack may caused by material defect, discontinuities in geometry or damage in service. Thus, Fracture Mechanics is introduced as a method for predicting failure of a surface containing a crack. This project is focusing on pre-existing crack with assumption that no microscopic defects are presents. Linear Elastic Fracture Mechanics (LEFM) is used to evaluate the Stress Intensity Factor (SIF) of the specimen. Further analysis is done by incorporating Elastic Plastic Fracture Mechanics (EPFM) to understand the crack growth over period of time. In this study, the important parameters in fracture mechanics such as Stress Intensity Factor (SIF), Crack Mouth Opening Displacement (CMOD), J Integral and stable crack growth are been investigated. A complex loading simulation of NKS-3 specimen is done using finite element modeling. The NKS-3 is a thick-tube used in Pressurized Water Reactor (PWR) which has a circumferential flaw on its inner surface. The cylinder is loaded with axial tensile load and internal pressure combined with thermal shock. A 2-Dimensional Axysimmetric-4 nodes element with focused mesh at the crack tip is employed in the simulation. Several analyses have been done using hardening data at different temperature. A comparison of solution is made for simulation with and without thermal load history. Further analysis showed that the stable crack growth is estimated to be around 3.0mm

Mechanical Properties of Medium Density Fibreboard Composites Material Using Recycled Rubber and Coconut Coir

Natural fibre reinforced composite has emerged as highly potential replacement for synthetic fibres. Various natural waste fibres have been adopted for various engineering applications. This paper investigates the mechanical properties of medium density fibreboard composites material fabricated using recycled rubber and coconut coir. The suitability of using recycled rubber and coconut coir as a raw material and polyurethane as a resin in the manufacturer of medium density fibreboard was also studied. The medium density fibreboards were fabricated at prescribed percentages of filler. The performance of composite was evaluated by its mechanical and physical properties. Experimental investigation indicated that the mechanical strength of medium density fibreboards such as modulus of rupture and modulus of elasticity increased with increasing board hardness. Overall, the results showed that medium density fibreboard had been produced with acceptable properties, thus providing alternatives to manufacturing and agricultures economic planning

Evaluating parallel simulated evolution strategies for VLSI cell placement

Simulated evolution (SimE) is an evolutionary metaheuristic that has produced results comparable to well established stochastic heuristics such as SA, TS and GA, with shorter runtimes. However, for problems with a very large set of elements to optimize, such as in VLSI placement and routing, runtimes can still be very large and parallelization is an attractive option. Compared to other metaheuristics, parallelization of SimE has not been extensively explored. This paper presents a comprehensive set of parallelization approaches for SimE when applied to multiobjective VLSI cell placement problem. Each of these approaches are evaluated with respect to SimE characteristics and the constraints imposed by the problem instance. Conclusions drawn can be extended to parallelization of other SimE based optimization problems

Finite Element Simulation on Damage and Fracture Properties of a Ring Cut from Filament-Wound Pipes with and without Delamination

The technological advances in various industries have increased the demands on new engineered material tremendously since conventional materials such as steel, failed to perform in severe conditions. Nowadays, composite materials especially fibre-reinforced plastic composites (FRP) are broadly being used in many engineering fields to manufacture critical components with high stress concentration, exposure to extreme surrounding or weight constraint. However, they often suffer from a characteristic weakness, i.e. they are prone to interlaminar damage, often in a form delamination. In order to assess the development and the consequences of such damage, interlaminar fracture properties are essential. In this study, the ring cut specimen from filament-wound pipes with and without delamination was modelled and simulated based on experimental work using finite element modelling to further assist the identification and determination of the fracture properties. Investigation also involves the effect of the delamination length to the Energy Release Rate, G. Comparison between 23mm delamination of simulation and experimental results from [7] is presented

Estimating the lifetime and Reentry of the Aluminum Space Debris of Sizes (1-10 cm) in LEO under Atmosphere Drag Effects

  This study concerns in addressing the lifetime and reentry of the space debris in LEO which extends from 200 to 1200 km. In this study the new Computer programs are designed to simulate orbit dynamics of space debris lifetime and reentry under atmospheric drag force by using Runge-Kutta Method to solve the differential equations of drag force and this model was adapted with the Drag Thermosphere Model (DTM78, 94), the Aluminum 2024 space debris in certain size (1-10 cm) were used in this study, which is frequently employed in the structure of spacecraft and aerospace designs. The selected atmospheric model for this investigation is the drag thermospheric models DTM78 and DTM94, because of this dependence on solar and geomagnetic activities. It has been found that the lifetime of the space debris increases with increasing perigee altitudes. It has been found that the elliptical shape of the debris orbit would change gradually into a circular shape, then its kinetic energy would be transformed into heat and hence debris destroy in the dense atmosphere

Decentralized Federated Learning Over Slotted ALOHA Wireless Mesh Networking

Federated Learning (FL) presents a mechanism to allow decentralized training for machine learning (ML) models inherently enabling privacy preservation. The classical FL is implemented as a client-server system, which is known as Centralised Federated Learning (CFL). There are challenges inherent in CFL since all participants need to interact with a central server resulting in a potential communication bottleneck and a single point of failure. In addition, it is difficult to have a central server in some scenarios due to the implementation cost and complexity. This study aims to use Decentralized Federated learning (DFL) without a central server through one-hop neighbours. Such collaboration depends on the dynamics of communication networks, e.g., the topology of the network, the MAC protocol, and both large-scale and small-scale fading on links. In this paper, we employ stochastic geometry to model these dynamics explicitly, allowing us to quantify the performance of the DFL. The core objective is to achieve better classification without sacrificing privacy while accommodating for networking dynamics. In this paper, we are interested in how such topologies impact the performance of ML when deployed in practice. The proposed system is trained on a well-known MINST dataset for benchmarking, which contains labelled data samples of 60K images each with a size $28\times 28$ pixels, and 1000 random samples of this MNIST dataset are assigned for each participant’ device. The participants’ devices implement a CNN model as a classifier model. To evaluate the performance of the model, a number of participants are randomly selected from the network. Due to randomness in the communication process, these participants interact with the random number of nodes in the neighbourhood to exchange model parameters which are subsequently used to update the participants’ individual models. These participants connected successfully with a varying number of neighbours to exchange parameters and update their global models. The results show that the classification prediction system was able to achieve higher than 95% accuracy using the three different model optimizers in the training settings (i.e., SGD, ADAM, and RMSprop optimizers). Consequently, the DFL over mesh networking shows more flexibility in IoT systems, which reduces the communication cost and increases the convergence speed which can outperform CFL

Molecular Characterization of the 16S rRNA Gene of Phytoplasmas Detected in Two Leafhopper Species Associated with Alfalfa Plants Infected with Witches' Broom in Oman

Two leafhopper species, Austroagallia avicula and Empoasca sp., were consistently found in alfalfa fields infected with witches’ broom phytoplasma (OmanAlfWB) in the Al-Batinah, Dakhliya, North and South Sharqiya, Muscat, and Al-Bureimi regions of the Sultanate of Oman. Phytoplasmas from both leafhoppers were detected by specific polymerase chain reaction (PCR) amplification of the 16S rRNA gene and the spacer region in direct PCR using P1/P7 primer pairs. Comparative RFLP profiles of the amplified rRNA gene and the spacer region from leafhopper phytoplasmas and from 20 phytoplasma controls yielded patterns referable to phytoplasmas belonging to the peanut witches’ broom group (16SrII group). In particular, extensive RFLP analyses with the endonucleases HpaII, Tru9I, Tsp509I, and RsaI indicated that the phytoplasmas in A. avicula and Empoasca sp. were identical but showed some differences from OmanAlfWB; however, RFLP patterns obtained with TaqI showed the OmanAlfWB and the phytoplasmas from the two leafhoppers to be identical. Direct PCR products amplified from phytoplasma leafhopper DNA using the P1/P7 primer pair were cloned and sequenced yielding 1758 bp and 1755 bp products from A. avicula and Empoasca sp. respectively; the homology of these sequences with OmanAlfWB and papaya yellow crinkle phytoplasmas was more than 98%. A phylogenetic tree based on the 16S rRNA gene and spacer region sequences from 44 phytoplasmas revealed that the phytoplasmas from the leafhoppers clustered with OmanAlfWB, papaya yellow crinkle, and gerbera phyllody phytoplasmas, all belonging to 16SrII group, but were distinct from lime witches’ broom phytoplasma, the most commonly found phytoplasma in the Sultanate of Oman