Procedia Structural Integrity最新文献

This paper investigates the comparative study of performance of two-way polypropylene fiber reinforced flat slab strengthened with BFRP (Basalt fiber reinforced polymer) fan and laminate against concentric loading. Three slabs of same dimension (1000 x 1000 x 135mm) were casted. Two slabs were reinforced with an optimum percentage (say 0.3%) of polypropylene fiber and one slab is taken as the control specimen. One of the slabs are Strengthened with BFRP string (obtained from basalt fabrics) having a fan shape as a new strengthening technique. For strengthening 16 double strand strengtheners were used and strengthened from a critical distance for punching shear of d/2 from the column face. Another slab is strengthened with basalt strip in a radial pattern.

The result reveals that the suggested strengthening technique increased the load carrying capacity and enhances the ductile behavior of the flat slab in comparison with the unstrengthen slab. These strengthening methods are capable of enhancing both maximum loading capacity and reduce the formation of retraction crack thus avoids brittle failures that may occur under line loading. This method of strengthening improves the bearing capacity of the slab without increasing the size of the structural components.

Plasma Transfer Arc (PTA) process uses the intense heat of electric arc to melt and fuse the 75Ni13.5Cr2.7B-3.5Si hard-facing alloy and the base metal. This process develops substantial residual stresses near the hard-faced surfaces during deposition and subsequent solidification and cool down. Furthermore, when a material interface is present, additional residual stress is formed because of the thermal strain mismatch of the dissimilar materials caused by their different thermal expansion coefficients. These stresses can cause cracks in the overlay during the component’s service life or even earlier during manufacturing which can lead to partial or total loss of the part structural integrity. To start optimizing the process to avoid these defects, it is necessary to know the residual stress distribution in the part and how it is related to the process parameters. Hard-faced components are having distinct microstructures with a step change in material properties, and this makes the residual stress measurement more challenging. This paper presents 2D residual stress maps of the deposit cross sections for PTA hard-faced samples using the contour method. This study is part of an ongoing research on the influence of process parameters on the residual stress and local microstructure of 75Ni13.5Cr2.7B-3.5Si clad 316 stainless steel.

The present work deals with the characterization of ductile tearing resistance of 1 mm thick interstitial free steel sheet using crack tip opening angle (φ), and δ₅ concepts with some experimental modification. CTOA (φ) measurements on the specimen surface at the growing crack tip have been performed using light microscope on both pre-cracked DENT and SENT specimens at three ramp rates following the essence of ASTM E 2472. In order to determine the effect of pre-cracking, CTOA of the notched (ρ:0.1 mm) SENT specimen has also been measured at 10^-4 s^-1. The transferability of φ−Δα and δ₅−Δα between two geometries has been verified. It is concluded that for a specified thickness both φ−Δα and δ₅−Δα plots can be used for crack growth characterisation of sheet metals even without using pre-cracked specimens. However, the angle φ(δ₅) determined from δ₅−Δα curve is not the true measure of optical CTOA,φ as the δ₅ gauge position does not follow the tip position of the growing crack.

In order to mitigate the effect of global warming and climate change by reducing CO₂ emission, clean energy options are being explored. Hydrogen generation using renewable energy like solar and wind is one of the clean energy options being considered. Four pillars of hydrogen economy are hydrogen generation, storage, transportation and consumption. The overall life cycle cost of these technologies will depend on the endurance of the material of construction used. Hydrogen is known to cause embrittlement in steels and in hydride forming metals, which can lead to early failure of the components used in hydrogen economy. The overall life cycle cost of these technologies can be significantly reduced if the operating parameters are so chosen to avoid susceptibility to hydrogen/hydride embrittlement or use materials, which are resistant to hydrogen/hydride embrittlement. Hence, investigation of the hydrogen/hydride embrittlement of the materials used during the hydrogen production, storage and transportation has to be in sync with technologies related to hydrogen energy. Significant work has been reported on hydrogen/hydride embrittlement of structural materials such as high strength steels, Ti-alloys, Zr-alloys, Nb-alloys used in power and process industries. The knowhow of the hydrogen/hydride embrittlement mechanisms of these materials will be of immense help in understanding the hydrogen/hydride embrittlement of newer materials of construction used in hydrogen systems. The mechanisms of hydrogen and hydride embrittlement will be discussed.

Aluminum Alloy is extensively used in aerospace and automotive industry due to its light weight and high strength properties. It is generally joined using Friction Stir Welding, which is a solid-state process. During this process residual stresses are developed in the welded region. It is a critical factor affecting the performance and lifespan of welded parts. Accurate measurement of residual stress is very important for ensuring the structural integrity of welded components. The conventional blind hole drilling method for residual stress estimation using the strain rosette, results error in the strain data capturing and compensating it is a challenging task. The omission of strain rosette is possible using the recently developed Digital Image Correlation in conjunction with Blind Hole Drilling. This paper focuses on the feasibility study of DIC in residual stress measurement. To accomplish this, Aluminum alloy AA6082 friction stir welded butt-joints are prepared. The residual stresses were measured at the top side of the weld joint using the DIC-BHD approach. At the weld top position, the transverse residual stress of -100 MPa approx. and the longitudinal residual stress of 118 MPa approx. were estimated.

Ever since the introduction of damage tolerance requirements in the aviation regulations, efforts continue to be made to prevent catastrophic failures due to damages present in the structure. It has also been realized that damage detection is the weakest link in the whole process of damage tolerance design to maintain continued airworthiness. The major components of the aircraft structure consist of both integral and riveted panels of sheets and stringers which are employed in fuselage skin panels, spar webs and stiffeners. In spite of all precautions, cracks or damages may arise in many of these primary structural members. These cracks cause stiffness degradation and reduce the total load-carrying capacity of the structure. In this paper, the damage tolerance behaviour of fuselage crown panel both integral and riveted stiffened panel configurations of Aluminium alloy 2024-T351 are studied using finite element based tools using crack growth analysis methods. The crack growth behaviour of both integral and riveted stiffened panels of aircraft fuselage having same geometrical configuration and subjected to uniformly distributed tensile loads is investigated. For this, a metallic stiffened panel with eight stringers, representative of crown panel of a transport aircraft fuselage is analysed with a centre skin crack propagating through the stringers. Stress intensity factors and fatigue crack propagation rates at the progressive crack tip of both types of the stiffened panels are computed by using Modified Virtual Crack Closure Integral (MVCCI) method. The stiffened panels fatigue crack growth rate was computed by using Paris law under constant amplitude fatigue loads. The analysis results show that integral stiffened panel causes higher stress intensity factor and less load bearing capability than riveted stiffened panel which has better damage tolerant capability in comparison to the integrally stiffened panel.

15-5 PH stainless steel is a martensitic precipitation-hardenable stainless steel (0.07C-15Cr-5Ni-3.5Cu-Fe). Presently, high strength low alloy steel, AFNOR 15CDV6 is used for the fabrication of Thrust Vector Control system of satellite launch vehicle. These pressure vessels are used for storing strontium perchlorate, intended for attitude (pitch and yaw) control of the launch vehicle during first stage. The tanks are fabricated through welding of rolled plates, machined rings, and end domes from forgings. AFNOR 15CDV6 steel is prone for corrosion and requires alumina barrier coating to protect from strontium perchlorate. Therefore, as a superior alternative, 15-5PH steel with improved corrosion resistance, simple heat treatment avoiding distortion was selected for the fabrication of pressure vessel. In order to improve the structural integrity of the pressure vessel, flow forming technology was adopted for realization of cylindrical portion of the tank, which eliminated the long seam weld joint and reduced the number of circumferential weld joints. As a part of the developmental program, the tank was designed, shells were flow formed and welded with end domes and were directly aged. The fabricated tank was subjected to a series of pressure tests followed by final burst test for estimating structural margins and ensuring quality requirements.

This paper describes the design of the pressure vessel, process followed for manufacture, qualification program adopted and detailed metallurgical analysis carried out on the burst tested hardware. The 15-5PH pressure vessel has successfully withstood the proof pressures and test results are better than the predicted analysis results, indicating structural integrity of the pressure vessel for flight.

The objective of this work is to evaluate the parameters of strain rate dependent Johnson-Cook material model using a hybrid procedure which uses finite element analysis as well as experimental data. The large strain rate tests were conducted to using split Hopkinson pressure bar test setup, whereas the quasi-static test was carried out using conventional testing machines. Johnson-Cook material model has been used to simulate the plastic deformation behavior of material under the high strain loading. This model provides the flow stress of the material as a function of equivalent plastic strain, plastic strain rate and temperature. The parameters, i.e., A, B, n, C and m of the model have been determined using a hybrid procedure as mentioned earlier. One of the important issues in split Hopkinson pressure bar testing is the variation of strain rate during the duration of loading. Due to decrease in reflected strain magnitude, the strain rate continuously decreases (as strain rate is proportional to reflected strain signal) and it is a characteristic of the above test method. However, this creates problem in evaluation of parameters of Johnson-Cook material model using conventional procedure. In this work, a modified procedure has been developed in order to take into account of this variation in strain rate as function of applied strain. The results of the method has been validated with experimental data. The parameters have been evaluated only for room temperature data and the effect of temperature shall be studied in future.

Ceramic materials used in mechanical applications show variations in their properties due to the presence of cracks. Micro-cracks within the material (size, orientation and density) affect the ceramic material’s strength and other mechanical properties. This study developed a micro-mechanics-based model that accounts for the original orientation of micro-cracks and their propagation as wing cracks. Unlike other micromechanics-based models, the current model defines failure based on entropy associated with crack propagation within the material. Entropy is calculated from energy dissipation from crack propagation from the pre-existing flaws in the ceramic. The Unified Mechanics Theory (UMT) is used to define entropy-based damage in the ceramic material, in which a parameter called thermodynamic state index (TSI) is employed to describe the state of the material. A representative volume element (RVE) with a pre-existing flaw is used to calculate the energy dissipated during the wing crack propagation. The effect of various crack lengths and orientations is incorporated with a probability density function. The strain rate effects are implemented using dynamic crack growth law. The stress-strain curve at strain rate from quasi-static to high strain rate (10^-3-10⁶) is plotted for Alumina under dynamic compression.

Probable risks of the Corrosion Preventive Compounds (CPCs) for the aviation riveted joints fatigue are considered. It is shown that high penetration of the CPCs can lead to the reduction of the riveted joints fatigue life. Negative side effect assumed to be result of the reduction of the friction between the mating elements.