Stress Analysis Technique Research Articles

Crack Growth Monitoring in Stainless Steels by Means of TSA Technique

In this work, the Thermoelastic Stress Analysis (TSA) technique was used for the monitoring of fatigue crack growth during fracture mechanics tests on stainless steel. In this regards, different methods are used in literature but most of them cannot be applied on real components since they require an off-line measurement of the crack.An automatic procedure based on TSA technique was proposed for the continuous evaluation of the crack tip position. Advantages with respect to classical methods can be obtained in terms of reduction of testing time, experimental set-up, data processing and data report.

Experimental Study of the Crack Growth in Stainless Steels Using Thermal Methods

Martensitic steels are used in the engineering fields where high temperatures, corrosive environments and high mechanical stress are required. In this work,theThermoelastic Stress Analysis (TSA) technique was used to characterize the fracture mechanics behaviour of twomartensitic stainless steels.TSA technique is proposed both for the monitoring in continuous way the crack position and for evaluatingthe stress intensity factor (SIF). An automatic procedure was developed capable to process very quickly the thermoelastic data acquired during the test. In this way, the Paris’ Law can be assessed reducing significantly the testing time.

A global–local theory with stress recovery and a new post-processing technique for stress analysis of asymmetric orthotropic sandwich plates with single/dual cores

While the 3D elasticity and the available local and zigzag theories encounter inaccuracies for very thin plates, results of the global theories become unreliable for thick plates with severe transverse variations in the material properties. In the present research, a quadratic finite element global–local sandwich plate theory with elasticity correction (stress recovery) is proposed for static stress and displacement analysis of sandwich plates with orthotropic face sheets and single or dual cores. Since the transverse shear stresses are derived based on the three-dimensional theory of elasticity, the continuity condition of the transverse shear stresses is satisfied at the interfaces between the layers, a priori. The presented theory not only leads to higher accuracies in comparison to the available high-order zigzag theories in some cases (especially, for soft or dual cores) but also it is computationally more economic. Results show that the results of the available zigzag and global–local theories may encounter inaccuracy problems not only for huge numbers of the sub-layers, but also for small numbers of the orthotropic layers.

A New Material Model for 2D FE Analysis of Adhesively Bonded Composite Joints

Effective and convenient stress analysis techniques play important roles in the analysis and design of adhesively bonded composite joints. A new material model is presented at the level of composite ply according to the orthotropic elastic mechanics theory and plane strain assumption. The model proposed has the potential to reserve nature properties of laminates with ply-to-ply modeling. The equivalent engineering constants in the model are obtained only by the material properties of unidirectional composites. Based on commercial FE software ABAQUS, a 2D FE model of a single-lap adhesively bonded joint was established conveniently by using the new model without complex modeling process and much professional knowledge. Stress distributions in adhesive were compared with the numerical results by Tsai and Morton and interlaminar stresses between adhesive and adherents were compared with the results from a detailed 3D FE analysis. Good agreements in both cases verify the validity of the proposed model. DOI: http://dx.doi.org/10.5755/j01.ms.20.4.5960

Absorption kinetics and swelling stresses in hydrothermally aged epoxies investigated by photoelastic image analysis

The present work proposes an experimental optical methodology able to measure the transient swelling stresses induced by the water uptake ageing of polymers. In particular, the work describes the implementation of a Photoelastic technique to quantify internal stresses arising during the hydrothermal ageing of cast epoxy samples. The material investigated is a model DGEBA/DDS epoxy system. Curing and post-curing cycles have been optimised in order to obtain a fully cured, high Tg, and completely stress free initial condition. Rectangular beam samples were then left in a hydrothermal bath at 90 °C, and regularly monitored by gravimetric and photoelastic analyses. The quantitative evolution of stresses induced by water ingress was obtained by a Photoelastic Stress Analysis technique applied during water absorption, and successive desorption in controlled conditions. The evolution of stresses is correlated with gravimetric data, allowing to gain a new insight to investigate the complex swelling and diffusion kinetics of water ingress into thermoset polymer networks.

Photoelastic stress analysis assisted evaluation of fracture toughness in hydrothermally aged epoxies

The present work has investigated the fracture toughness of a model DGEBA epoxy system subject to Hidro-Thermal aging. A Photoelastic Stress Analysis technique has been implemented, showing the evolution of stresses arising throughout the water uptake process due to the non-uniform swelling of the material. Gravimetric and Dynamic Mechanical Thermal Analyses have further complemented the characterization, showing the onset of plasticization effects with aging. The correlation of all previous characterizations has allowed to conclude that an increase of KIC fracture toughness is obtained at the fully saturated condition. In particular Photoelasticity has also revealed the onset of relevant swelling induced stresses during the first stages of water absorption, leading to an increase of fracture toughness due to compressive stresses settling near the crack tip. A stress free condition is instead reestablished at the later stages of absorption, suggesting that the increased toughness of the saturated material is an effect of the modifications induced by aging on the polymer structure.

Prediction of notch sensitivity effects in fatigue and in environmentally assisted cracking

AbstractSemi‐empirical notch sensitivity factors q have been used for a long time to quantify notch effects in fatigue design. Recently, this old concept has been mechanically modelled using sound stress analysis techniques, which properly consider the notch tip stress gradient influence on the fatigue behaviour of mechanically short cracks. This mechanical model properly calculates q values from the basic fatigue properties of the material, its fatigue limit and crack propagation threshold, considering all the characteristics of the notch geometry and of the loading, without the need for any adjustable parameter. This model's predictions have been validated by proper tests, and a criterion to accept tolerable short cracks has been proposed based on it. In this work, this criterion is extended to model notch sensitivity effects in environmentally assisted cracking conditions.

On the Tolerance to Short Cracks under Fatigue and SCC Conditions

The fatigue behavior of mechanically short cracks that depart from notch tips can be mechanically modeled using sound stress analysis techniques which properly account for the notch tip stress gradient influence on their growth rates, considering the basic fatigue properties of the material, its fatigue limit and long crack propagation threshold, and all the characteristics of the notch geometry and of the loading, without the need for any data fitting parameter. This model's predictions have been validated by proper tests, and a criterion to accept tolerable short cracks has been proposed based on it. In this work, this criterion is extended to model notch sensitivity effects in environmentally assisted cracking conditions.

Universal technique for stress analysis of beam elements of articulating cranes in case of dynamic load

Universal technique for stress analysis of beam elements of articulating cranes in case of dynamic load

Advanced Techniques of Stress Analysis

This article aims to check the stress analysis technique based on 3D models also making a comparison with the traditional technique which utilizes a model built directly into the stress analysis program. This comparison of the two methods will be made with reference to the rear fuselage of IAR- 99 aircraft, structure with a high degree of complexity which allows a meaningful evaluation of both approaches. Three updated databases are envisaged: the database having the idealized model obtained using ANSYS and working directly on documentation, without automatic generation of nodes and elements (with few exceptions), the rear fuselage database (performed at this stage) obtained with Pro/ ENGINEER and the one obtained by using ANSYS with the second database. Then, each of the three databases will be used according to arising necessities. The main objective is to develop the parameterized model of the rear fuselage using the computer aided design software Pro/ ENGINEER. A review of research regarding the use of virtual reality with the interactive analysis performed by the finite element method is made to show the state- of- the-art achieved in this field. Key Works: analysis stress, safety margins, parametric modeling

Lock-In Signal Post-Processing Techniques in Infra-Red Thermography for Materials Structural Evaluation

This paper describes the potential of off-line thermographic signal processing by means of Lock-In Correlation algorithms, in order to implement structural health monitoring and stress analysis techniques. Thermal datasets acquired by infrared thermocameras are locked-in and correlated numerically with opportune reference signals, and amplitude and phase values of various harmonics retrieved by means of a Fast Fourier Transform and time averaging based filtering. This information is then processed for NDT defect probing and for evaluating the Thermoelastic Effect induced temperature changes. Two case studies in particular are discussed, implementing the proposed signal lock-in processing: a Thermoelastic Stress Analysis of a Brazilian disc under cyclic compression, and NDT of a delaminated polymer matrix composite panel. The NDT case study evidences the ability of the lock-in algorithm to analyse the response of the component to multi-frequency modulated heat waves, while both case studies demonstrate the potentials of the off-line signal treatment to enable low cost thermal setups.

Thermoelastic Stress Analysis - Emerging Opportunities in Structural Health Monitoring

The emergence recently of a thermoelastic stress analysis (TSA) capability exploiting low-cost, compact and rugged microbolometer detector technology provides a significant opportunity topromote a broader use of this powerful non-contact full-field stress analysis technique. An area whereit has considerable and hitherto unexplored potential is in in-situ structural health monitoring (SHM).The present paper outlines the case for a nexus between SHMand TSA in this new form. It is proposedthat the approach should yield diagnostic and prognostic capabilities surpassing those of some existingSHM modalities. An F/A-18 centre-fuselage full-scale structural fatigue test is employed as a casestudy to illustrate the practical feasibility of the approach and to underscore some of its potential.Although the case study focuses on an aircraft structure, the concept has potential application to awide variety of different engineering assets across the aerospace, civil and maritime sectors.

Increase of Fatigue on Piston and Connecting Rod in Using Supercharger

This research deals with analysis the fatique and the failure of piston engine using FEA.The objective of this research is to develop the geometry of piston engine using solidwork software and to investigate the maximum stress using stress analysis techniques to predict the failure of piston and connecting rod and identify the critical locations of the components of EF7 engine with supercharger and without supercharger. The finite element model of the components was analyzed the static stress with linear material model . first we discuss the amount of increased pressure in cylinder by supercharger and turbocharger then the influence of the inlet air pressure on the naturall aspirated engine which the main parts of its engine are not reinforced is taken account,then the result is showed the stress is increased by quantity of 273 MPA on piston and connecting rod which make the increase of fatigue on pistons and connecting rod and decrease in its period of working.The results can also significantly reduce the cost to produce the piston,and improve product reliability and improve the fatique strength and durability.

Stress analysis in single molar tooth

The human tooth faces different stresses under environments of different loading conditions, these loading produces major factors in weakness of the tooth and bone structure. The need to save natural teeth has prompted the development of novel and complex techniques in endodontology, prosthodontics and periodontology. Despite a poor long-term prognosis and some prejudice to local bone, considerable efforts have been exerted for the realization of these techniques. Nowadays, the 3D finite element analysis (FEA) is one of the more recently used techniques for stress analysis in single human tooth under different loading cases. The von Mises stress distribution indicated that the greatest effort area of tooth lies at the base of crown up to the gingival line with varying intensities in the different loading cases. The highest stress in the cortical bone was predominantly found around the cervical region of the tooth and lowest in the cancellous bone and periodontal ligament (PDL). The PDL is a soft tissue, and it could function as an intermediate cushion element which absorbs the impact force and uniformly transfers the occlusal forces into the surrounding bone.

Optimizing Residual Stress Profile Induced by Laser Shock Peening Using DOE Technique

The control of residual stress is crucial in ensuring the integrity of engineering components and Laser Shock Peening (LSP) process can be used to good effect to introduce the beneficial compressive residual stress levels required. It is, however, difficult to use normal laser peening control systems to establish the ideal peening conditions that will result in the best component performance. This paper presents results from a study to optimise the laser peening parameters for a typical titanium super alloy used in high performance turbine blade by investigating how the main peening process parameters influence residual stress profiles resulted by numerical simulations. Statistical Design of Experiments (DoE) was used to limit the number of experiments required for optimisation to be possible. Using this technique and numerical depth profiling methods for residual stress analysis, the maximum compressive residual stresses in Ti-6Al-4V were measured for a range of peening conditions. The results of the detailed process characterisation investigations have shown that, by using careful DoE, it is possible to fully optimise the laser shock peening process to obtain greater benefits than would be possible with traditional control processes.

Studies of residual stress measurement and analysis techniques for a PWR dissimilar weld joint

For evaluation of the PWSCC crack propagation behavior, a test model was produced using the same fabrication process of Japanese PWR plants and the stress distribution change was measured during a fabrication process such as a hydrostatic test, welding a main coolant pipe to the stainless steel safe end and an operation condition test. For confirmation of validity of the numerical estimation method of the stress distribution, FE analysis was performed to calculate the stress distributions for each fabrication process. From the validation procedure, a standard residual stress evaluation method was established. Furthermore for consideration of characteristics of PWSCC’s propagation behavior of the dissimilar welding joint of the safe end nozzles, the influence coefficients at the deepest point for the stress intensity factors of axial cracks with large aspect ratio a/c (crack depth/half of surface crack length) was prepared. The crack shape was assumed a rectangular shape and the stress intensity factors at the deepest point of the crack were calculated with change of crack depth using FE analysis.By using these stress distribution and influence coefficients, a behavior of a PWSCC crack propagation at the safe end nozzles can be estimated easily and rationally.

A hybrid technique for residual stress analysis through stress function fitting

This work presents a hybrid experimental theoretical technique for residual stresses analysis of mechanical components. It was used the blind hole technique along with the Electronic Speckle Pattern Interferometry (ESPI) method and Airy stress functions for the determination of the principal stress components. Displacement information is fitted in order to extract Airy stress function coefficients. The results demonstrate that this technique is of great utility to determine the average principal stress and local stress gradients.

Measurement of Thermomechanical Coupling and its Application in Stress and Damage Analysis

Polymer composites are increasingly being used in high-end and military applications, mainly due to their excellent tailorability to specific loading scenarios and strength/stiffness to weight ratios. The overall purpose of the ongoing research at the University of Southampton is to develop an enhanced understanding of the behaviour of fibre reinforced polymer composites when subjected to a range of loading scenarios. The measurements lecture reviews progress in using the thermoelastic stress analysis technique as a tool that enables a better understanding of the behaviour of polymer composite single skin and sandwich structures.

Stress Field Evolution under Mechanically Simulated Hull Slamming Conditions

The effect of repeated loading from mechanically simulated hull slamming on foam core sandwich composites was investigated utilizing a novel technique that simultaneously measured temperature and displacement while cyclic loading occurred. Thermoelastic Stress Analysis (TSA) and Digital Image Correlation (DIC) techniques were combined using a single infrared camera for characterization of the foam core. Improved stress fields with TSA results were found through deformation compensation. Initial work approximating hull slamming conditions mechanically utilizing a custom device were performed. Mechanically loading offers several benefits over water impact investigations, including easy access to the sample during the slamming event, an unobstructed optical path, and accelerated testing. Evolving stress fields under long-duration, repeated simulated hull slamming loading were observed around a growing delamination crack between the foam core and skin.

Numerical Simulation for Composite Wing Structure Design Optimization of a Minitype Unmanned Aerial Vehicle

To improve performances of minitype unmanned aerial vehicle (UAV) wing, numerical simulation and optimization design principle was carried out for designing best composites wing structure. Thus tradeoff can be obtained between general performance and weight of wing. Advanced composite material has its own outstanding features, such as high specific strength, high specific modulus, designable performance and integral forming easily. The application of advanced composite material on aerocraft can significantly reduce weight, and improve aerodynamic and flight performances. In this paper, parametric finite element model is established using parametric modeling technique for stress and stain analysis. Given any set of geometric parameters, geometric modeling, meshing, strain and stress analysis can be automatically carried out in sequence. The global optimal solution is guaranteed by proposed two-step optimization search strategy combing genetic algorithm (GA) and sequential quadratic programming (SQP). Comparative studies show that optimization efficiency can be greatly improved with two-step optimization search strategy. As a kind of new material, advanced composite material brings about great revolution to aerocraft industry since it was introduced in 1960s. With its wide application in aerospace structure, advanced composite material is named as the four main materials of aerospace structure along with aluminum alloy, titanium alloy, and alloy steel. The advanced composite material has its own prominent features, such as high specific strength, high spe- cific modulus, designable performance and integral forming easily, etc. With application of advanced composites, weight of aerocraft can be reduced by about 25% ~ 30% compared to conventional metal structures. Moreover, aerodynamic and flight performances can be improved to levels that conventional materials can hardly achieve. The extensive application of advanced composites is also able to promote some further technology development of stealth and intelligent design. The aerocraft performance is significantly dependent on part and quality of advanced compo- sites used in aerocraft. However, it is difficult to achieve good designs of composites in aerocraft to guarantee requirements for different missions. Therefore, to fully explore directional properties of composites, designable ability of performance and excellent manufacturability of large component integral forming, it is necessary to introduce principle of optimization to composite design (1-6). In this paper, optimization design and numerical simulation for composite of wing on a UAV is