Evaluation Of Stress State Research Articles

A CAE approach for the stress analysis of gear models by 3D digital photoelasticity

The use of numerical and experimental methods to determine the stress field of mechanical components is well known. In particular, 3D photoelasticity can be considered the only experimental technique for the complete stress state evaluation of 3D components. The advent of rapid prototyping techniques has allowed the manufacturing of complex models in a matter of hours by using birifrangent materials. The present paper is focused on the description of a Computer Aided Engineering (CAE) approach which combines Finite Element (FE) simulations and automatic photoelastic investigations for the stress analysis of face gear drives, made by stereolithography. Computer Aided Design (CAD) geometries, used to manufacture the stereolithographic models, are directly used to perform FE analyses, thus allowing the stress analysis process to become simpler and easier. The substantial agreement observed between experimental and numerical results proved the potentialities of the adopted approach and the usefulness of FE simulations to optimize photoelastic analyses through cost- and time-effective experiments even for complex 3D shapes.

CRITICAL DEPTH OF NORMAL CRACKS IN REINFORCED CONCRETE BEAMS OF RECTANGULAR CROSS-SECTION

The evaluation of stress state of longitudinal tensile reinforcement is highly important while examining the technical state of under-reinforced concrete structures. The appearance of yield stress in tensile reinforcement could be treated as the start of incipient failure of the flexural structure. The state of tensile reinforcement of flexural reinforced concrete structures could be examined by observing the properties of normal cracks. This paper presents the analysis of the relationship between various parameters of a normal crack during its development. Some elements of fracture mechanics are used for analysis of stress state in flexural reinforced concrete members. The analytical data are compared to the experimental results, and the adjustment functions are proposed for flexural beams of certain cross section shape, dimensions and reinforcing ratio.

Predicting residual and flow stresses from surface topography created by laser cutting technology

The paper deals with the engineering method for laser cutting technology that utilizes stress equations derived from surface topography for determining residual stresses. It presents an original method for residual stress assessment in a non-contact and non-destructive manner. The high temperature around cut edges results in the development of residual stresses during the cutting process, which decreases the quality of the end product. Surface topographical parameters themselves carry information on a concrete state of technological process in the concrete moment of its usage. This method for the assessment of residual stress in materials being cut by a laser beam provides sufficient information on the residual stress state evaluation with sufficient accuracy by applying an analytical and experimental approach. Experiments were conducted on three different materials, namely steel, aluminium alloy and titanium. It was necessary to check calculation by measuring the residual stress distribution in the vicinity of cut edge using the ultrasonic method. The novelty of the method for the determination of residual stresses in a workpiece lies in the physics-based approach focusing on the mechanical and stress-deformation parameters of the material being cut and on the mechanical equilibrium of the system: material properties—tool properties—deformation properties.

Stress-Strain Analysis of Sand Subjected to Triaxial Loading

An influence of the end boundary conditions to distribution of stress and strains in a soil specimen during conventional compression triaxial tests is analyzed by the experimental and numerical methods. An evaluation of actual stress state is important when determining the shear strength parameters of soil. These methods are used in this paper to investigate and simulate the contact between the testing equipment and ends of sand specimen during the test. Two different conditions of sample boundaries are analyzed:the first case, when the friction between the sample ends and testing machine is not eliminated (fixed ends); the second case, when the friction between the sample ends and testing machine is eliminated (free ends). The friction is eliminated by allowing the sample base to move freely in any horizontal direction. Simulation results of stress-strain distribution in the sample by using the finite element method show that the shear stress at the contact plane increases for the sample with fixed ends. The stress restricts the displacement of sample ends in the horizontal direction. In the case of free ends the horizontal displacement of sample base occurs. Similar to simulation results have been obtained from the laboratory tests performed with triaxial compression apparatus.

Reliability Provision of Rod Shells of Steady Roofs over Stadium Stands at Stage of Design Work

The design work of the spatial pivotal roof with a cut-out in the elliptic setting formed by the system of rigid threads through the sections based on determination of a numerical safety index of a designed structure has been described. The proposed method provides the sequence of solution of problem series: determination rational geometric parameters of a structure; obtaining of appropriate rigidity characteristics of basic bearing elements; determination of a track of elements destruction for typical coating diagram with the following evaluation of stressed and strained state of an object; determination of numerical safety indices of a structure (determination of the lower and upper safety limits).

Durability Study of a Machine Shaft Based on the Material Behavior of 41Cr4 Steel Subjected to Rotating Bending

This paper presents the durability analysis of a machine shaft subjected to bending with torsion, based upon the stress analysis at a notch which joins segments of different cross-sections (circular and square respectively) of the shaft. During the specific operating conditions of the equipment which’s part the shaft is, this notch has proven to be critical, causing premature failure. The durability analysis is carried out based on the real loading conditions, allowing the stress state evaluation at the base of the notch for different radii, using ABAQUS 6.9-3 finite element analysis program. The experimental studies carried out on the shaft’s material, 41Cr4 steel, resulted in the determination of material properties and of torsion fatigue curves in case of two different heat treatments. The cycles composing the equivalent stress spectrum are counted using the rainflow algorithm. The number of loading blocks to failure (number of load spectrum repetitions), considering the real operating conditions, is obtained using Miner’s rule, based on the rotating bending fatigue curve, corrected corresponding to the shaft’s specific characteristics. The proposed calculation method, based on the variation in time of the stress tensor during operating conditions, leads to the determination of the optimal notch radius for which the shaft’s durability falls between prescribed limits.

Comparative measurements of the stress state in a rolled carbon steel using magnetic Barkhausen noise and ultrasonic method

We report the results of the stress evaluation of rolled carbon steel cantilever using different non-destructive methods. The paper describes the procedure of calibration and measurements using Barkhausen effect and ultrasonic method. Test object is constant stress cantilever submitted to different loads. Both methods complement and provide better reliability of the stress state evaluation.

Evaluation of Near-Surface Stress States in Asphalt Concrete Pavement

A sophisticated three-dimensional (3-D) tire model was placed directly on a three-layer asphalt concrete (AC) pavement system to form a 3-D tire–pavement contact model. The model was then verified with measured contact stresses and was used to investigate near-surface stress states in the AC layer. When compared with the traditional uniform vertical loading model, the 3-D tire–pavement contact model produced stress states not only higher in magnitude but also more variable in distribution. The 3-D tire–pavement contact model produced much higher principal tensile stress and maximum shear stress near the tire edge; the increased stress was a possible explanation for instability rutting and associated top-down cracking. A critical shear plane was developed for the top 50 mm of the AC layer by using a p-q diagram, and the tire–pavement contact model produced a much higher shear yield percentage.

Acoustoelastic effect in concrete material under uni-axial compressive loading

This study deals with the general matter of non-destructive evaluation of pre-stressed structures in civil engineering. Usually such structures are composed of concrete and are steel reinforced. Proposed idea is the evaluation of mechanical stress state of a concrete body (instead of steel cables) via ultrasonic non-destructive evaluation (NDE), by using the link between ultrasonic velocities and mechanical stresses provided by the acoustoelasticity theory. Velocities of the ultrasonic waves (longitudinal and transversal with different polarizations) are observed during propagation through a concrete body submitted to uni-axial loading (compressive testing). Obvious variations in velocity are found depending on the mechanical stress state (e.g. Δ c=92 m/s at σ=16 MPa for longitudinal waves). Thus acoustoelastic behavior of concrete is demonstrated. Further analyses provide acoustoelastic coefficients of concrete about ten times higher than the common ones of steel. The feasibility of stress evaluation using ultrasounds in concrete structures is proved under laboratory conditions.

Acoustic Emissions in Borosilicate and epoxy resin composite

In this paper a research looking for to extend the acoustic emission (AE) technique from the evaluation of stress state of rock samples to know its composition is presented. For this purpose the rock samples were simulated by a composite made of a resin and borosilicate spheres. The epoxy resin playing the role of country rock and Borosilicate spheres represent the coarse grain. These samples were undergone to uniaxial compression test and the AE signals were recorded and studied looking for the identification of each material characteristic spectrum. The spectral analysis of these recorded signals shown that it is possible to identify the characteristic spectra of each material from the full spectra of composite.

Strength and stressed state of asymmetric mechanically inhomogeneous welded joints with incomplete fusion at the center of the weld under biaxial loading

An approximate solution of the plane problem of the theory of plasticity for main pipelines, cylindrical vessels, and shell structures subjected to biaxial loading is proposed which allows one to perform theoretical analysis aimed at evaluation of strength and stressed state of asymmetric mechanically inhomogeneous welded joints with incomplete fusion at the center of the weld in the case of ductile fracture. Regulating the degree of mechanical inhomogeneity and thickness of the soft interlayer, it is possible to get the uniform strength of welded joints with incomplete fusion and shift fracture processes to the base metal under biaxial tension. We also determine the range of sizes of the domain of incomplete fusion for which the uniformity of strength is attained for the joint with asymmetric mechanical inhomogeneity of the butt weld with incomplete fusion.

BIDIMENSIONAL FINITE ELEMENT ANALYSIS OF SPUR GEAR: STUDY OF THE MESH STIFFNESS AND STRESS AT THE LEVEL OF THE TOOTH FOOT

The purpose of this work is to determine the spur gear mesh stiffness and the stress state at the level of the tooth foot. This mesh stiffness is derived from the calculation of the normal tooth displacements: local displacement where the load is applied, tooth bending displacement and body displacement [15]. The contribution of this work consists in, basing on previous works, developing optimal finite elements model in time calculation and results precision. This model permits the calculation of time varying mesh stiffness and the evaluation of stress state at the tooth foot. For these reasons a specific Fortran program was developed. It permit firstly, to obtain the gear geometric parameters (base radii, outside diameter,…) and to generate the data base of the finite element meshing of a tooth or a gear. This program is interfaced with the COSMOS/M finite element software to predict the stress and strain state and calculate the mesh stiffness of a gear system. It is noted that the mesh stiffness is periodic and its period is equal to the mesh period.

A theoretical model for general cross section wires stress state evaluation during non-linear bending

Non-linear bending of thin wires is the main or one of the fundamental topics in several applications, especially when the plastic behaviour is widely involved. Tyre manufacturing and helical spring design are some of the most classical examples, but continuous improvement is also required in designing spectacle frames and shape memory wires. In this paper, a new analytical model is proposed, to foresee the final curvature obtained after non-linear bending of wires with nonsymmetric cross sections, once the loading parameters are known. Obviously both elastic springback after unloading and material behavioural non-linearities have been considered in the model. From an engineering point of view, negligible errors are committed if BernoulliNavier's hypothesis is guaranteed. The wire stress state can be evaluated by means of the model and enables the low cycle fatigue resistance verification.

Feasible Evaluation of Flow Properties and Stress State of Structural Materials Using Instrumented Indentation Tests

Flow properties and stress state are indispensable factors for safety assessment of structural materials in operation, which were evaluated using instrumented indentation tests (IITs). Flow properties were obtained by defining representative stress and strain, and IIT results for 10 steel materials were discussed by comparing with those from uniaxial tensile tests. The indentation load-depth curve is significantly affected by the presence of residual stress, and the stress-induced load change was converted to a quantitative stress value. The stress state of a friction stir-welded joint of API X80 steel was evaluated and compared with that measured by energy-dispersive X-ray diffraction.

Analytical evaluation of stress state in braided orthotropic composite cylinders under lateral compression

This paper deals with the analytical modelling of elastic stress state inside RTM-moulded braided composite cylinders under lateral compression. Taking into account the radial stresses, our modelling is based on the Fourier series development of the π-periodic symmetric loading, deriving from the Hertzian contact law. The experimental part describes the quasi-static delamination under lateral compression of RTM-moulded carbon–epoxy rings, made from braided two-dimensional (2D) tubular preforms and DGEBA-IPD resin. The theoretical part shows a mesoscopic computation of transverse shear stresses is needed in order to explain the locations of the brittle failures. We eventually introduce the notion of an equivalent virtual major crack occurring at a critical value of displacement in order to provide a simplified representation of crack onset and energy release.

Clinical evaluation of hormonal stress state in medical ICU patients: a prospective blinded observational study

To evaluate whether classification of patients as having low, moderate, or high stress based on clinical parameters is associated with plasma levels of stress hormone. Prospective, blinded, observational study in an 18-bed medical ICU. Eighty-eight consecutive patients. Patients were classified as low (n=28), moderate (n=33) or high stress (n=27) on days 0 and 3 of ICU stay, based on 1 point for each abnormal parameter: body temperature, heart rate, systemic arterial pressure, respiratory rate, physical agitation, presence of infection and catecholamine administration. The stress categories were: high: 4 points or more, moderate 2-3 points, low 1 point. Plasma growth hormone (GH), insulin-like growth factor 1 (IGF-1), insulin, glucagon, cortisol were measured on days 0 and 3. Plasma cortisol and glucagon were significantly higher and IGF-1 lower in high vs. low stress patients on days 0 and 3. High stress patients were more likely to have high cortisol levels (odds ratio 5.8, confidence interval 1.8-18.9), high glucagon (8.7, 2.1-36.1), and low IGF-1 levels (5.9, 1.8-19.0) than low stress patients on day 0. Moderate stress patients were also more likely to have high cortisol and glucagon levels than low stress patients. Insulin and GH did not differ significantly. Results were similar for day 3. Moderate and severe stress was significantly associated with high catabolic (cortisol, glucagon) and low anabolic (IGF-1) hormone levels. The hormonal stress level in ICU patients can be estimated from simple clinical parameters during routine clinical evaluation.

Evaluation of notch root elasto-plastic stress–strain state for general loadings using an elastic solution

A method is proposed for the evaluation of the elasto-plastic notch root stress and strain states using an elastic solution for an isotropic and homogeneous structure subjected to general loadings. Materials of von-Mises type obeying a multilinear strain hardening rule are considered for the present study. The yield zone around the notch root is assumed to be well contained and the analysis is based on the incremental deformation theory. It is observed that, due to relaxation and redistribution of stresses at the notch root, a fraction of the total elastic strain energy density is conserved during inelastic deformation at the notch root. In the present study the fractional contribution is evaluated using a proportionality function, which is shown to be constant for a given linear hardening material, and independent of the loading and geometry of the structure. Moreover, it has been noted from the study that the proportionality function is a linear function of normalized tangent modulus for the plane stress case, whereas it is a quadratic function for plane strain. The stresses and strains evaluated using the proposed method are in close agreement with finite element solutions.

A new interlayer approach for CVD diamond coating of steel substrates

A Ni/Cu/Ti multilayer system is proposed to face the typical problems-related with direct diamond deposition on steel substrates, namely the lack of adhesion and growth rates. Systematic experimental work allowed achieving the best MPCVD parameter set in order to obtain both thin and thick diamond films (5–130 μm) with good morphology and adhesion with low residual stress level. In fact, a thick soft copper layer permits to accommodate the thermally-induced stresses during the cooling stage of MPCVD process, allowing good diamond film integrity. The films thus obtained are continuous and uniform, crack-free and well adhered as required in most mechanical applications. The characterization techniques were: Scanning electron microscopy (SEM) to observe morphology; μ-Raman spectroscopy to check diamond film quality and stress state evaluation; X-ray diffraction to measure the residual stresses; micro-indentation to examine the diamond film adherence; profilometry to measure the surface roughness.

A new interlayer approach for CVD diamond coating of steel substrates

A Ni/Cu/Ti multilayer system is proposed to face the typical problems-related with direct diamond deposition on steel substrates, namely the lack of adhesion and growth rates. Systematic experimental work allowed achieving the best MPCVD parameter set in order to obtain both thin and thick diamond films (5–130 μm) with good morphology and adhesion with low residual stress level. In fact, a thick soft copper layer permits to accommodate the thermally-induced stresses during the cooling stage of MPCVD process, allowing good diamond film integrity. The films thus obtained are continuous and uniform, crack-free and well adhered as required in most mechanical applications. The characterization techniques were: Scanning electron microscopy (SEM) to observe morphology; μ-Raman spectroscopy to check diamond film quality and stress state evaluation; X-ray diffraction to measure the residual stresses; micro-indentation to examine the diamond film adherence; profilometry to measure the surface roughness.

Evaluation of stress states in metals using stochastic model for deformation : Journal of JSNDI, Vol. 46, No. 4 p. 293 Kato, M.; Sato, T.; Kameyama, K.; Kosugi, Y.

Evaluation of stress states in metals using stochastic model for deformation : Journal of JSNDI, Vol. 46, No. 4 p. 293 Kato, M.; Sato, T.; Kameyama, K.; Kosugi, Y.