Papers by Keyword: Damage Tolerance

Abstract: In the quantitative characterization of linear defect structure of Piston Alloy, non-destructive testing and micro-morphology of defect, shape and outline of prefabricated linear defect are used in this paper. Based on ANSYS finite element software, an experimental simulation of line defect was carried out by using the finite element software of micromechanics. The defects of piston alloy components are assigned with material parameters, the model grid is divided, the boundary condition is defined and the finite element simulation is carried out under ANSYS/Mechanical environment. The calculation of the micro-stress field of the interface with various defects is obtained. Under the service condition of high-power density diesel engine, the local stress concentration caused by line defect is less than the strength limit of alloy material. Therefore, in this location eddy current testing non-destructive testing control line defect size is 0.12 mm×0.2 mm×5 mm. It is suitable for Eddy current nondestructive testing of piston components and can ensure the material safety and work reliability of Piston components under service condition.

Abstract: This paper mainly studies the position of the contact surface of the first ring groove of the piston under the condition of thermal mechanical coupling under the service conditions of the piston component of high-power diesel engine at the temperature of 350°C-420°C and the detonation pressure of the piston top of 28Mpa. For typical NDT defects such as surface crac0k, internal crack, shrinkage cavity and cold lap, the sensitivity of scale, morphology and position and their quantitative relationship. The crack defect on the upper joint surface of the piston ring causes the maximum stress in the range of 56.8 MPa-81.3 MPa. Among them, 8% of the circumference of a single defect will cause material damage and failure. Defects larger than this scale must be detected in eddy current NDT.

Abstract: The defects of high-power density piston aluminum alloy components involved in this paper include surface crack, internal crack, shrinkage cavity and cold shut. The service condition of piston components is 350°C-420°C, and the explosion pressure of piston crown is 28Mpa. The requirements for eddy current flaw detection of this component are in accordance with a and requirements in GB / T5126-2013 eddy current flaw detection standard, that is, it is not allowed to be greater than 0.12mm × 0.2mm × 3mm volumetric defects, and Ф1.0mm flat bottom hole equivalent point defect. For the piston components of 88kw / L high-power diesel engine, under the service conditions of temperature 350°C-420°C and piston top explosion pressure 28Mpa. Under the condition of thermal mechanical coupling, the typical NDT defects such as surface crack, internal crack, shrinkage cavity and cold shut of the first ring groove and internal position of the piston are studied. On scale, morphology and position sensitivity and their quantitative relationship. At the same time, numerical simulation analysis combined with relevant experimental verification is used to comprehensively analyze and evaluate the damage tolerance of defects, and scientifically evaluate the defects of different properties and sizes.

Abstract: Mechanical properties of several composite materials were assessed in order to establish their suitability for unmanned aerial vehicle components manufacturing. The materials under evaluation consisted in E-glass fiber (satin/twill weave) impregnated with polyester, respective epoxy resin. The study was focused on two mechanical tests: low-velocity impact and tensile tests. Based on the results obtained, it was observed that configurations reinforced with twill weave presented higher tensile strength compared with satin reinforced configurations. Moreover, they presented a lower damage degree in case of impact tests. It was concluded that fabric quality has a considerable influence on the impregnation process and on the composite material mechanical properties. In the present case, the twill weave impregnated with epoxy resin can be used to manufacture small range UAV components.

Abstract: In this paper, the effect of carbon fiber hybridization on the compressive strength of glass-carbon/epoxy hybrid filament wound pipes before and after low velocity impact was investigated experimentally. Specifically, the effects of different stacking sequence and fiber content ratio on the compression and compression after impact (CAI) behavior of hybrid glass-carbon fiber reinforced polymer pipes were analyzed. Hybrid composite pipes composed of eight layers of / reinforced with thin HDPE liner were manufactured utilizing filament winding technique. A series of axial compressive tests were carried out on the composite pipes for the non-impacted and impacted specimens under 100 J of impact energy. Residual compressive strength, damage tolerance and failure modes were examined and analyzed for different pipe configurations, before and after the impact. The failure modes of non-impacted and impacted composite pipes under compressive loading were analyzed visually. The results show that, under the same conditions of impact energy, specimens with alternative fibers exhibited better impact resistance regardless of fiber content ratio. Moreover, carbon fiber reinforced epoxy specimens exhibited the worst impact damage tolerance for a given impact energy level although having the highest compressive strength before impact among the samples, with the highest percentage reduction of 62% in residual compressive force after impact.

Abstract: This article investigated the fatigue crack growth behaviors in the novel TC32 titanium alloy with bimodal and basket-weave microstructures, which were respectively obtained by the convectional (α+β) phase forging and quasi-β forging processing. Results showed that at the same level of tensile performance, the basket-weave microstructure had a lower fatigue crack growth rate than the bimodal microstructure, as the basket-weave microstructure had a more tortuous crack path, a rougher fracture surface and more secondary cracks. All these served to improve the fatigue crack growth resistance, which attributed largely to the effects of crack closure. Moreover, secondary cracks grew primarily along the α/β interfaces for the basket-weave microstructure but directly went across the colony-type lamellar (α+β) phase and the primary α phase without obvious regularity for the bimodal microstructure.

Abstract: In this work, a method for determining the Equivalent Initial Flaw Size (EIFS) distribution using the Boundary Element Method (BEM) is proposed. Maximum Likelihood Estimation (MLE) is used to infer the EIFS distribution of a cracked stiffened panel under multiple sources of uncertainty, including uncertainty in the loading conditions, fatigue crack growth model parameters, and in the measurement of crack size found from routine inspections. Results suggest that MLE is an effective tool for estimating the parameters of an EIFS distribution when no prior knowledge is available regarding the EIFS distribution or its parameters.

Abstract: Sandwich composite materials are widely used in various applications, due to their advanced flexibility in responding to special design requirements. This paper presents the evaluation of thick sandwiches, aimed to be imbedded in platforms of a green energy unit, accommodating storage water tanks. The evaluation of the damage tolerance was made having in view previous studies on similar materials and covered assessment of results obtained during low velocity impact tests and post-impact tests, aimed to establish the residual mechanical performance. Ways to increase the damage tolerance, by diminishing the invasive effect of low velocity impact, were also explored.

Abstract: In this paper, the damage behaviour of aerospace composite structures has been studied. The analysed structure is an all-composite wing with inter-laminar manufacturing induced damage. The manufacturing induced delaminations are located at the leading edge on the extrados and in the area near the fuselage. Different analyses have been performed to correctly predict the pre-existent damages evolution under service loading conditions. Preliminary linear buckling analyses have been performed to check for instability of the delaminations under service loads; then the risk of delaminations’ propagation has been evaluated by means of a Virtual Crack Closure Technique based approach.

Abstract: Al containing intermetallic phases have been evaluated in various bcc and fcc steels. Attractive application options have been derived for hot working tools steels with respect to a reduction of resource critical alloying elements and in cold formable steels by the combined density reduction and strength increase.