Stress Correction Factor Research Articles

Second-order Stiffness Matrix and Loading Vector of a Tapered Rectangular Timoshenko Beam-column With Semirigid Connections

The second-order stiffness matrix and loading vector of a linearly tapered Timoshenko beam-column with rectangular cross-section, constant width and generalized end conditions subject to a constant axial load is derived. The proposed model includes the simultaneous effects of: (1) axial load (tension or compression) applied at both ends; (2) transverse load; (3) generalized end conditions; (4) bending and shear deformation along the member; (5) shear stress correction factor induced by the tapering of the cross section; and (6) the shear force induced by the applied axial load as the member deflects laterally using two different approaches, those by Engesser and Haringx which are proportional to the total slope (dy/dx) and to the angle of rotation (θ) along the span of the member, respectively. The governing differential equations are solved by the power series method. The concept of fixity factor of tapered Timoshenko beam-columns with semirigid end connections is introduced. The proposed method and corresponding equation are capable of determining the static and stability behavior of elastic framed structures made of tapered beam-columns with semi-rigid connections using a single segment per element. Three comprehensive examples are presented that show the accuracy and validity of the proposed method and the calculated results are compared with those obtained using ABAQUS.

Development of cone-wedge-ring-expansion test to evaluate the tensile HOOP properties of nuclear fuel cladding

We report the development of a cone wedge ring expansion test method to determine the tensile hoop properties of irradiated nuclear fuel cladding in a hot cell. A closed-form solution was developed to explicitly relate the hoop stress σθ to the axial piston loading using the scale factor χ and the shear stress correction factor α, where the χ and α factors are used to convert the applied piston load and the radial dilatation of the ring into the tensile hoop stress-strain curve. The applicability of this new test method was demonstrated by successfully evaluating ring specimens of Zr-4 alloy to failure. The ring specimens deformed uniformly in the axial and circumferential directions until onset of necking. The χ and α factors were successfully determined by using a finite-element stress analysis that benchmarked with applied test load and total work to account for frictional forces and the associated energies dissipation between the different sliding components of the testing system. The tensile hoop strength values obtained using the proposed cone-wedge-ring-expansion test method were 10% higher than values obtained from the tensile evaluation of the cladding material along the axial direction. The variability in results was found to be within the range reported in the literature.

Fatigue Constrained Topological Structure Design Considering the Stress Correction Factor

Fatigue Constrained Topological Structure Design Considering the Stress Correction Factor

Generalized spiral torsion spring energetic model

Torsional springs or coil springs are used to apply a torque and obtain a rotation of its shaft. They are usually manufactured with flat steel. Recommended maximum operating stresses in static applications are given as a percentage of tensile strength. These values could be consulted in an experimental table with an appropriate stress correction factor. An energetic model for torsional spiral springs is presented in this work. First of all a parametric study analyzes different variables which affect the spring performance. Main variables analyzed have been the length of the spring strip, strip thickness and height, housing diameter, shaft diameter, variation of bending stiffness and curvature along the length of the spring strip. Afterward, the analysis of energy storage in coil spring is carried out. There are two causes why energy storage is less than the maximum of the model developed. The first one is energy wasted in coil contact and in spring blocking and unblocking process. The second cause is that the torque applied to spin is less than the one which reached the yield strength in spring section. Both of them are quantified and incorporated in the model. At the end the energetic model is used to calculate the torque–angle turned curve, framework deformation and the spring-framework contact force. Model developed is validated with test on a monolithic fiberglass spiral spring.

A Numerical Simulation of Probability Study on Fatigue Fracture of Heavy Machinery

The construction of heavy machinery is giant, of which the propagation process of fatigue crack is complex, there is big difference when different model of fatigue crack growth was selected in estimating its residual life. For this problem, a three stages method of assessment for crack propagation process is divided which include surface cracks, center penetrate cracks and edge through crack. and the characteristics what the stress intensity factor is changing with crack size is considered, based on probability fracture theory, the model in three stages fatigue crack growth which is used to estimate remaining life is established under constant amplitude loading. By the numerical simulations of Monte-Carlo, the survival line of 50-97% probability or P-S-N curve were obtained, also the sensitivity analysis about which the initial size of surface crack effects to the total life was given. It was shown that the time of surface crack propagation which has a closer relationship with the thickness of the plate occupies a large proportion of the total life, and the effect of the center and edge cracks can be ignored when the thickness of the plate is more than 12×10−3 finally, the experience range of the stress correction factor was given. the results can be regarded as theoretical foundation for estimation of fatigue residual life under about heavy machinery in amplitude and random load.

MEMS Packaging Reliability in Board-Level Drop Tests Under Severe Shock and Impact Loading Conditions—Part II: Fatigue Damage Modeling

Damage in handheld electronic devices due to accidental drops is a critical reliability concern. This paper is the second of a two-part series and focuses on damage models for drop test durability of commercial off-the-shelf microelectromechanical systems (MEMS) components that are mounted on printed wiring boards. The modeling approach is based on the experimental results presented in the first part of this two-part series. In particular, the focus of this paper is on damage due to drop events under extremely high accelerations (20 $000g$ , where $g$ is the gravitational acceleration) achieved by a series of secondary impacts. Impacts with such high accelerations can occur in handheld electronic devices due to collisions between internal neighboring structures and can generate stress levels well beyond levels previously anticipated in typical use, or in conventional qualification tests. A calibrated dynamic multiscale finite element model is used to evaluate the stresses at the relevant failure sites. Utilizing the local stress at each failure site, a fatigue damage modeling approach is proposed to predict the interaction of the competing failure mechanisms in MEMS components. The proposed damage model is based on the deviatoric stress (or strain) at the failure site and uses a hydrostatic stress correction factor to address the influence of mean stress (depending on component orientation). The model estimates the damage accumulation rate for a given stress condition and integrates the accumulated damage over the entire response history. This approach makes it possible to address the influence of the post-impact transient response on fatigue damage accumulation. The damage-model constants are determined for each failure site of interest by relating the failure data to the corresponding stress/strain metrics. Damage modeling results are not only capable of matching the lifetimes of MEMS components in drop testing, but also provide an explanation of transitions in dominant failure sites observed in MEMS assemblies under different drop conditions.

Stress interference calculation model and its application in volume stimulation of horizontal wells

A new model for calculating stress fields of fractured media was established by incorporating stress correction factor based on displacement discontinuity boundary element method. The accuracy of the new model is close to 3D displacement discontinuity model, and its calculation is significantly simplified. An algorithm for multi-fracture propagation geometry was proposed based on fracture criterion and fracture growth rate law, which was used to investigate multi-fracture stress interference and propagation geometry. The results show that the size of stress interference is determined by the shortest dimension of fracture face, which is 1.2−1.5 times fracture height when fracture length is longer than fracture height, and 1.2−1.5 times fracture length when fracture length is shorter than fracture height. The larger the ratio of fracture spacing to fracture height, or the smaller the ratio of net pressure to the differential principle stress, the more close to well-bores the deviation position is, and the larger the deviation angle is. The middle fracture propagates to the fracture at a further distance and one dominating fracture propagates longest when three-cluster fractures are not equally spaced, while the middle fracture propagates straightly when three-cluster fractures are equally spaced.

Discretized Markov chain in damage assessment using Rainflow cycle with effects of mean stress on an automobile crankshaft

We studied the effect of mean stress correction factor using the Rainflow counting technique to assess the fatigue damage of an automobile crankshaft under service loading by considering the stochastic process of the Markov chain. The failure of the crankshaft will cause serious damage to the engine and also to other connecting subcomponents. The service loading is computationally generated from the Discrete Markov chain model and the fatigue cycle is counted using the Rainflow counting technique with the consideration of the local minima and maxima load. To quantify the fatigue damage, the strain-life curve using the fatigue mean stresses was used to model the fatigue failure of the material used in for the crankshaft at Nf = 106. The fatigue mean stresses were used to estimate the effects of the mean stress on the fatigue strength of the component under service loading condition. Statistical verification with the boundary condition of the 90% confidence level was performed to observe the difference between the stochastic algorithms when compared towards the fatigue life behavior of the ductile cast iron material. We concluded that for the practical application, the proposed stochastic model provides a highly accurate assessment of fatigue damage prediction for improving the safety and controlling the risk factors in terms of structural health monitoring.

Mean stress effect correction in strain energy-based fatigue life prediction of metals

A new mean stress corrected strain energy model is proposed for fatigue life prediction of metals. Specifically, a mean stress sensitivity parameter is incorporated into modify the dissipated strain energy by introducing two mean stress correction factors. The prediction accuracy of the proposed model is compared with those of Walker, Smith–Watson–Topper, Morrow, and generalized damage parameter models by using 13 experimental data sets. All data points for each material are, respectively, fitted into a single mean stress corrected strain energy-life curve. More accurate predictions are achieved by the proposed model for all data sets with lower model prediction errors than others.

Effects of confining stress, density and initial static shear stress on the cyclic shear response of fine-grained unclassified tailings

A constant-volume direct simple shear apparatus was used to investigate the effects of confining stress, initial static shear stress and void ratio on the liquefaction resistance of fine-grained tailings. The cyclic resistance ratio (also expressed as the overburden stress correction factor) was found to decrease with increasing confining stresses in the range 100–400 kPa and to gradually increase from 400 kPa onwards, when samples were tested at the same initial void ratio. The presence of an initial static shear stress decreased the liquefaction resistance. A key outcome of the work was to reveal the critical importance of density on liquefaction susceptibility of compressible tailings. Thus, a combined correction factor to account for overburden stress and density on cyclic resistance was proposed.

Cyclic DSS tests for the evaluation of stress densification effects in liquefaction assessment

To evaluate the stress correction factor for the Cyclic Resistance Ratio (“CRR”) under cyclic loading with principal stress rotation, 86 Cyclic Direct Simple Shear (CDSS) tests were performed on two sands, one from Ain Beniam, in Alger, Algeria, and another from Coimbra, Portugal. These sands have distinctive grain shapes and size distributions and were tested with various relative densities and under different initial effective confining stresses. The results of the tests performed with zero initial static shear stress – therefore with the static shear stress factor Kα equal to one – indicate that the values of confining stress level correction factor, Kσ, as currently recommended, seem to underestimate the cyclic resistance.

Estimation of tooth form factor for normal contact ratio asymmetric spur gear tooth

To estimate the tooth form factor for a loaded symmetric spur gear tooth, some normalized standards like International Organization for Standardization (ISO) and American Gear Manufacturers Association (AGMA) are available. However, the tooth form factor for a loaded asymmetric spur gear tooth cannot be estimated through the available standards. An asymmetric spur gear tooth is one whose drive side pressure angle is different from the coast side pressure angle. In the present work, the standard ISO B methodology has been adapted suitably for estimating the tooth form factor and the stress correction factor in asymmetric spur gear tooth. Also, the critical root fillet parameters (critical root tooth thickness, bending moment arm and radius of curvature) and the tooth form factor for asymmetric spur gear tooth with several sets of drive side and coast side pressure angles are determined through an adapted ISO method and a comparative study with FEM is also carried out.

A simplified model of a reinforced square hollow section T-joint for stress evaluation in bus superstructures

This study aims to create a simplified model of a reinforced square hollow section SHS T-joint found in bus superstructures. The approach is to use a combination of one-and two-dimensional finite element models to represent a reference three-dimensional finite element model of the joint and determine stress correction factors as functions of the geometrical variables of the joint. This approach requires the stiffness of the simplified model to be equivalent to that of the reference model. By using a stiffness error function and a three-factor design of experiment DOE, the best of four trial models, with minimum average stiffness error, was identified. The stress correction factors were then determined under static in-plane bending loads. A polynomial regression model was used to construct the relationship between the stress correction factors and the thickness-to-width ratios of the joint. The correlation coefficient of 0.9845 indicated a strong relationship and the t score confirmed its significance.

Low Cycle Fatigue Analysis of after Treatment Device Induced due to Thermal Load by Using Finite Element Analysis

Cyclic thermal loading causes cyclic thermal stress and thermal fatigue in the component. The goal of this paper is to characterize the thermal fatigue behavior of after-treatment (AT) device, i.e. Exhaust Gas Processor (EGP) and prediction of crack initiation cycles. The paper contains transient thermal analysis to map temperature on EGP model. By taking temperature distribution as input, Elasto-plastic structural analysis is done. Based on stress-strain data and fatigue material property, crack initiation cycles are estimated. For low cycle fatigue analysis, strain based approach, i.e. Brown-Miller Criteria with Morrow mean stress correction factor [1] is used. The von-Mises stress and crack initiation cycles are investigated and S-N curve and Ɛ-N curve are compared with standard graphs.

Allowable Bending Fatigue Stress of Rails

Allowable bending fatigue stress is an important input for rail section design because of the nature of repeated loading on railways. The majority of rail failures have their origin in fatigue. In the American Railroad Engineering and Maintenance-of-Way Association (AREMA), there is only a fatigue test under the name of rolling load test for bonded joints; there are no fatigue tests for parent rail and welded joints. With respect to bonded joints, there is no known railroad or transit agency that uses plain bonded joints as an alternative to either flash butt weld (FBW) or alumino thermite weld (ATW) joints. A rail or weld should be able to resist at least 2 million stress cycle repetitions without developing any cracks. In this paper, allowable bending fatigue stress is formulated analytically with the nominal stress method (S-N). Marin’s six modification factors are applied to the laboratory-determined fatigue limit to account for surface conditions, size, load, temperature, reliability, and shape. Then, Goodman’s mean stress correction factor is applied to account for mean tensile stress in the rail. A brief literature review on the modification factors is included. The allowable bending fatigue stress is calculated and validated theoretically, then compared with the recommended AREMA value. Finally, the current AREMA formula and its recommended value for allowable bending fatigue stress are discussed.

Estimation of Ultimate Lateral Load Capacity of Piles in Sands Using Calibration Chamber Tests

Abstract Current practice for the estimation of the ultimate lateral load capacity of piles is typically based on the vertical effective stress σ′v, while the effect of the lateral effective stress σ′h is not specifically considered. In the present study, calibration chamber lateral pile load tests are conducted to investigate the load response and ultimate lateral load capacity Hu of laterally loaded piles under various soil and stress conditions. In order to determine Hu from load-deflection curves, different criteria are explored and analyzed. From the test results, it is shown that Hu increases significantly with increasing σ′h for a given σ′v. It is also found that lateral deflection of pile at ultimate state tends to increase as the relative density and lateral stress increase. On the basis of the test results, the lateral stress correction factor reflecting the effect of the lateral effective stress σ′h on Hu is proposed. From the test results, it is seen that the proposed procedure using the lateral stress correction factor produces more realistic estimation of Hu. Case examples are selected from the literature and used to compare results measured and predicted using the proposed approach.

A Multiaxial Fatigue Reliability Analysis Method of Casing Drilling in Casing String

The Von Mises equivalent stress criteria is used to equivalent convert and correct the uniaxial and biaxial fatigue reliability experimental study of the casing material. And the probabilistic fatigue P–S–N curve of the casing is gained. The fatigue limit and fatigue life in test is equivalent convert to actual casing by combined stress correction factor. A multiaxial fatigue life calculation formula is proposed by correcting the probabilistic fatigue P–S–N curve.

The shear ramp: A new test method for the investigation of coated fabric shear behaviour – Part II: Experimental validation

The shear ramp is a new test method for the investigation of coated fabric shear behaviour. The implementation of the method with a biaxial test rig is given and compared to the off-axis biaxial extension of a specimen with 45° oriented fibres. Based on experimental observations and finite element analyses, it is shown that both test methods give similar results for a wide range of coated fabrics if the proper stress correction factors are used. An estimation of these factors is given for both test methods for PVC–polyester as well as PTFE–glass fabrics.

A new low cycle fatigue criterion for isothermal and out-of-phase thermomechanical loading

A new multiaxial low cycle fatigue criterion based on a damage parameter is presented as an attempt to condition energy based approaches for the general common use in isothermal and thermomechanical out-of-phase loading. The damage parameter is based on the dissipated plastic strain energy per cycle, with a stress correction factor to account for mean and maximum stress influences, and a thermal term to account for elevated temperature damages. With such a formulation, the low temperature damaging regime (dislocations glide) can be separated from the high temperature one (diffusion processes). Oxidation and creep damages are accounted for in an implicit manner. The prediction capability of the present criterion is compared with that of other classical lifetime criteria using data from uniaxial isothermal and out-of-phase thermomechanical fatigue (TMF) tests performed on three cast iron families which are relevant for different internal combustion engine components. The result is higher prediction accuracy and a capability to estimate TMF lifetime by calibrating on isothermal fatigue tests only, leading to a great potential cost saving for future test programs given similar materials and loading conditions.

A.S.P.E.N. Clinical Guidelines: Nutrition Support of the Critically Ill Child

careful selection of the appropriate mode of feeding and monitoring the success of the feeding strategy. The use of specific nutrients, which possess a drug-like effect on the immune or inflammatory state during critical illness, continues to be an exciting area of investigation. The lack of systematic research and clinical trials on various aspects of nutrition support in the PICU is striking and makes it challenging to compile evidence based practice guidelines. There is an urgent need to conduct well-designed, multicenter trials in this area of clinical practice. The extrapolation of data from adult critical care literature is not desirable and many of the interventions proposed in adults will have to undergo systematic examination and careful study in critically ill children prior to their application in this population. In the following sections, we will discuss some of the key aspects of nutrition support therapy in the PICU; examine the literature and provide best practice guidelines based on evidence from PICU patients, where available. While some PICU popu lations include neonates, A.S.P.E.N. Clinical Guidelines for neonates will be published as a separate series.