Papers by Keyword: Damage

Abstract: The damage state in a formed component has a significant influence on the performance of the component in service. Controlling damage evolution during forming through specific modifications of the process parameters will therefore allow an improvement of this performance. The evolution of the stress-strain state during the forming process is the primary influencing factor of the resulting damage state. The stress-strain state is influenced by the friction between tools and workpiece. To investigate the cause-effect relationship between friction and damage evolution in the deep drawing process, Finite Element simulations of the deep drawing of rotationally symmetric cups were performed. Punch velocity and blank holder force were varied. Damage was predicted using a Lemaitre damage model. The damage states predicted using a Coulomb friction law and a model incorporating a dependence on contact normal stress and relative velocity were compared. The parameter-dependent friction model predicted a change in the damage distribution after forming when varying the process parameters, which was not found using the Coulomb friction law.

Abstract: A finite element model of a small, high-speed glass fiber-reinforced polymer (GFRP) craft is presented to simulate the impact of slamming on the bottom of the hull. The behavior patterns of the model are based on the results of laboratory experiments in order to verify the use of a viscoelastic sheet in absorbing the energy of impact damage by modifying the laminate of the hull. The stacking sequence for the model is obtained using a sample from a typical ship sailing in the Galapagos Islands. The FEM model shows the variations in energy absorption by comparing them with strain and damage–strain energy. The benefits of the viscoelastic modification are verified, and its use is proposed for the construction and modification of ships that support destructive slamming loads.

Abstract: In the process of layer inspection and hole mending, it was found that the corrosion of tubing in a well was serious, and perforation and fracture occurred. Part of the tubing was found to be cracked from the failed pipe samples, and relatively serious pitting corrosion pits were found on the surface of the outer wall. The fracture morphology and corrosion products were analyzed by means of macroscopic analysis and metallographic microscope, SEM and EDS. The result show that the mechanical damage of the outer wall of the tubing was the primary condition for accelerating corrosion, and the severe corrosion thinning of the inner and outer walls of the tubing was the main reason for the failure of the tubing string. The corrosion perforation of tubing was mainly caused by internal corrosion.

Abstract: For the design of vessels built by GFRP laminates, an insert with a viscoelastic layer is proposed to reduce the spread of damage produced by the vertical impact of the ship's bottom with the sea or slamming phenomenon. Using vertical drops-weight impact machine that reproduce the energy inferred to the panel during navigation, the propagation of the damage of OoA cured prepreg panels is studied comparing it with modified panels with insertion of viscoelastic layer. The use of acceleration data reading allows the benefits of viscoelastic modification during impact to be quantified through the developed formulation. The force, displacement and energy returned by the panel after impact have also been quantified, which does not become intralaminar and interlaminar damage. It is shown that under 40 joules of impact, the viscoelastic sheet has its best ability to return energy and above 130 joules it loses its capacity.

Abstract: In recent years, clinching has gathered popularity to join sheets of different materials in industrial applications. The manufacturing process has some advantages, as reduced joining time, reduced costs, and the joints show good fatigue properties. To ensure the joint strength, reliable simulations of the material behaviour accounting for process-induced damage are expected to be beneficial to obtain credible values for the ultimate joint strength and its fatigue limit. A finite plasticity gradient-damage material model is outlined to describe the plastic and damage evolutions during the forming of sheet metals, later applied to clinching. The utilised gradient-enhancement cures the damage-induced localisation by introducing a global damage variable as an additional finite element field. Both, plasticity and damage are strongly coupled, but can, due to a dual-surface approach, evolve independently. The ability of the material model to predict damage in strongly deformed sheets, its flexibility and its regularization properties are illustrated by numerical examples.

Abstract: A method for manufacturing the titanium alloy NT-50 nanofibers (1-20) microns in a composite assembly is proposed. The undamaged nanofibers production conditions are determined. Nanofibers are used to create new products: diagnostic sensors for ophthalmology.

Abstract: This paper focus on evaluation of behavior, damage and failure processes occurring during the loading cycles in the carbon fiber reinforced composite by acoustic emission method. Since acoustic emission is physical phenomenon that detects the released energy in form of waves spreading through the material due to stimulation of material by external or internal stress, it is possible to evaluate complex damage and failure processes. For that purpose, the standard and open holes tensile testing specimens with different number of plies were manufactured. Selected acoustic emission parameters were correlated with data obtained from mechanical test. Linear localization method together with signal analysis using Fast Fourier transform algorithm were used as another tool for detection and evaluation of spreading damage processes inside the composite during the load. Basic damage types inside the composite material were identified by metallographic analysis using light microscopy. More complex damage processes were observed on the fracture surface using stereomicroscopy and scanning electron microscopy.

Abstract: The possibility of increasing crack resistance, strength and elastic modulus of polymer-containing compositions due to the directed organization of their structure by internal, external and complex activation is investigated. Filled polymer compositions are presented as open complex dynamic systems. This made it possible to use rational fillers and special matrix-transformer of external electromagnetic influences as factors for controlling the processes of their structure formation and hardening to obtain materials with the required properties.

Abstract: Channeling phenomena during ion implantation have been studied for 50 keV ¹¹B, 100 keV ²⁷Al and 240 keV ⁷¹Ga in 4H-SiC by secondary ion mass spectrometry and medium energy ion backscattering. The same projected range are expected for the used energies while the channeling tails are shown to be substantially different, for example, channeled ⁷¹Ga ions may travel 5 times as deep as ¹¹B. Ion implantation has been performed both at room temperature (RT) and 400 °C, where channeling effects are reduced for the 400 °C implantation compared to that of the RT due to thermal vibrations of lattice atoms. The temperature effect is pronounced for ⁷¹Ga but nearly negligible for ¹¹B at the used energies. The channeling phenomena are explained by three-dimensional Monte Carlo simulations. For standard implantations, i.e. 4° off the c-direction, it is found that a direction in-between the [000-1] and the <11-2-3> crystal channels, results in deep channeling tails where the implanted ions follow the [000-1] and the <11-2-3> directions.

Abstract: The friction of ship main engine mechanical moving parts, combined with the internal combustion of fuel, generate a great amount of heat, leading to the increase of their running temperature and acceleration of their wear. If the temperature and wear phenomena are not controlled and kept within the maker’s thresholds, it will result in a partial or total damage of the propulsion system. However, the oil lubrication system plays a vital role in reducing the friction of the moving parts and ensuring their cooling and cleaning. Therefore, it must be reliable enough and continuously available for a safe operation of the main engine. This work aims at studying the main engine lubrication oil system’s reliability. This will be achieved through using Bayesian Network method, in order to identify the system components weak points to improve their reliability and to propose a highly reliable system that may either be installed on board of a conventional ship or an autonomous ship. The benchmark of the improved system and the formal system shows a significant enhancement in reliability that has become close to 1. In the case of an autonomous ship, this system must operate autonomously without human intervention. An autonomous and remote monitoring system concept is proposed. In case of system failure or need of change of its functioning parameters, the shore control center team takes over the control and executes the necessary adjustment remotely.