Preload Stress Research Articles

In-situ stress analysis using the anelastic strain recovery (ASR) method at the first offshore gas production test site in the eastern Nankai Trough, Japan

To evaluate in-situ stresses by applying the anelastic strain recovery (ASR) method to drilling cores, four cores retrieved from different depths between 265 and 313 m below seafloor in a well at the first offshore gas production test site in the eastern Nankai Trough, Japan were utilized to measure anelastic strains onboard the drilling ship. The onsite ASR measurements suggest this depth range in the study area is a normal faulting stress regime dominated by gravitation. In subsequent laboratory experiments, the cores were returned to their in-situ stress states via the K0 consolidation procedure, then elastic and anelastic strains were measured during and after the unloading process to verify the onboard measurements and quantify in-situ stresses. These laboratory calibration experiments verified that the ASR measurements following the stress release could provide reasonable estimates for the artificially applied preload stress.

Pre-Load Stress Echocardiography for Predicting the Prognosis in Mild Heart Failure

ObjectivesThis study sought to introduce and confirm the efficacy of pre-load stress echocardiography with leg-positive pressure (LPP) for improving risk stratification of patients with mild stable heart failure. BackgroundHeart failure patients with mild symptoms and a poor prognosis should be identified and treated aggressively to improve clinical outcome. MethodsWe performed transthoracic echocardiography with LPP in 202 patients with chronic cardiac disease. Twenty-two of these patients also underwent cardiac catheterization, and left ventricular pressure was measured during LPP along with simultaneous Doppler recordings. Patients were classified into 3 groups on the basis of their left ventricular (LV) diastolic dysfunction as assessed by transmitral flow velocity: restrictive or pseudonormal (PN) at rest, impaired relaxation (IR) at rest and during LPP (stable IR), and IR at rest and PN during LPP (unstable IR). Clinical outcome was compared among these groups. ResultsThe LPP increased LV end-diastolic pressure from 15.8 ± 4.7 mm Hg to 20.5 ± 5.0 mm Hg in the unstable IR group and from 10.5 ± 2.6 mm Hg to 14.7 ± 3.8 mm Hg in the stable IR group (both p < 0.001). During an average follow-up of 548 ± 407 days, 5 patients had cardiac death, 37 had acute heart failure, 4 had an acute myocardial infarction, and 7 had a stroke. The all-cause cardiac event rate in unstable IR was higher than in stable IR (p < 0.001), and was similar in the PN group (p = 0.81). Event-free survival was significantly lower in unstable IR than in stable IR (p = 0.003). In a Cox proportional hazards model, unstable IR was an independent predictor of all-cause cardiac events (hazard ratio: 8.0; p < 0.001). ConclusionsThe left LV end-diastolic pressure-volume relationship can be estimated by changes in transmitral flow velocity during LPP. Thus, pre-load stress echocardiography using LPP provides additional prognostic information in mild heart failure beyond that provided by conventional Doppler echocardiography at rest.

Effect of preload stress on the dynamic response of 9%Cr heat-resistant steels with various microstructures

With a uniaxial oscillation load coupled to different preload stresses, the dynamic responses of 9%Cr heat-resistant steels with different microstructures (martensite and cell structure) were measured on a low-cycle fatigue machine at the elevated temperature of 823K. The experiment results show that the internal friction of 9%Cr heat-resistant steel is dependent on not only the microstructure, but also the preload stress. The internal friction of 9%Cr heat-resistant steel with martensite reaches the minimum when the preload stress is close to half of its 0.2% offset strength. Within the present range of preload stress, however, the internal friction of cell structure monotonically increases with the preload stress. Based on the analysis of obtained results, it indicates that for the 9%Cr heat-resistant steels with martensite and cell structure, the different behaviors of internal friction with the preload stress are mainly attributed to various dynamic configurations of internal defects.

The effects of sulfide stress cracking on the mechanical properties and intergranular cracking of P110 casing steel in sour environments

Variation and degradation of P-110 casing steel mechanical properties, due to sulfide stress cracking (SSC) in sour environments, was investigated using tensile and impact tests. These tests were carried out on specimens, which were pretreated under the following conditions for 168 hours: temperature, 60 °C; pressure, 10 MPa; H2S partial pressure, 1 MPa and CO2 partial pressure, 1 MPa; preload stress, 80% of the yield strength (σs); medium, simulated formation water. The reduction in tensile and impact strengths for P-110 casing specimens in corrosive environments were 28% and 54%, respectively. The surface morphology analysis indicated that surface damage and uniform plastic deformation occurred as a result of strain aging. Impact toughness of the casing decreased significantly and intergranular cracking occurred when specimens were maintained at a high stress level of 85% σs.

Buckling of an Adhesive Polymeric Micropillar

Adhesion and buckling of single PDMS micropillars were investigated as a function of compressive preload. The micropillars had diameters of 10, 12, 14, and 20 μm and aspect ratios of 1 to 3.3. Adhesion generally increased with a decrease in the aspect ratio. A dependence of pull-off strength on the compressive preload stress was found for micropillars that underwent buckling. When buckling was reversible, tip contact recovered upon unbuckling, which resulted in only a slight reduction of adhesion. In situ observation studies identified irreversible buckling, i.e., lack of tip-contact re-formation, resulting in adhesion loss. It is concluded that the edge radius of the tip, which acts as a circumferential crack, controls adhesion. Fibril buckling is found to be broadly consistent with the predictions of Euler buckling theory.

Optimum design of hybrid composite multi-ring flywheel rotor based on displacement method

A structure optimum design based on the displacement method has been performed to maximize the energy storage capacity of a hybrid composite multi-ring flywheel rotor. In the process of optimal design, the preload stress generated by interference assembly, the fiber material failure and the delamination between two adjacent rings under high speed rotation are all considered. Four types of the optimal schemes of energy storage capacity, energy per unit mass (EPM), energy per unit volume (EPV), energy per unit cost (EPC) and energy per unit mass and cost (EPMC) are proposed to satisfy the needs of different applications and optimal designs are carried out by using a sequential quadratic programming (SQP). The optimal results show that all composed rings of the hybrid flywheel rotor can nearly reach the limits of strength in both radial and circumferential directions, and simultaneously the rotor is at the critical state of delamination. The radius parameters and the maximum allowed rotational speed of the hybrid composite flywheel are closely related to the optimal schemes. Considering the effects of angular acceleration and gravity on the delamination will result in the decreasing of energy storage capacities for four typical applications.

Revealing load hysteresis based on electronic speckle pattern interferometry and physical mesomechanics

A method to reveal load hysteresis of metal specimens is described. In this method, a low-level tensile-load is applied to a previously loaded specimen, and the resultant displacement field is visualized as a two-dimensional, whole-field image. An optical interferometric technique known as the Electronic Speckle Pattern Interferometry is used for the visualization. The interferometric fringe pattern of the visualized displacement field is analyzed for determination of the degree of deformation from the previous load. A series of experiments have been conducted with aluminum plate specimens for the demonstration of this method. The specimens are preloaded to three stress levels: (A) lower than the yield stress, (B) middle of the plastic regime, and (C) close to the maximum stress. After released from the preload, the specimens are reloaded for fringe pattern analysis. It has been found that the fringe patterns clearly differentiate the three preloading conditions, and that by varying the reload stress level it is possible to reveal the preload stress quantitatively. All experimental observations are explained by deformation dynamics based on physical mesomechanics.

Experimental Study of Integrated Multilayer Clamping High Pressure Vessel

The hydrostatic test of integrated multilayer clamping high pressure vessel is performed from 15.7 MPa to 56.52 MPa (1.8 times of the design pressure). The measured stress values have deviation from the Lamè equation (maximum error 34%). The inner wall stress is low while the outer wall stress is high. The layered vessel mechanics model is deduced to analyze the deviation. The inner shell is an external pressure vessel and the outer shell is the internal pressure vessel. The contact of the inner shell and the outer shell generates preload stress. The multilayer structure parameter is a universal nondimensional parameter to calculate the preload stress of layered vessel, and the corrected theory values have smaller error in high pressure (less than 10%). The super hydrostatic test alters the preload stress distribution and the gaps between layers.

Multi-Layer Pressure Vessel Contact Analysis

The multi-layer pressure vessel generates the preload stress during the process of wrapping &amp; clamping. The contact between the wrapped layers and the inner shell is the source of the preload stress. The contact mechanics model shows the primary mechanics relationship, and the contact pressure vessel causes the local settlement. The theory contact pressure has 5% error with simulation value. The experiment values of inner wall are coincided with the theory stresses, and the largest error between the theory and the experiment is below 16.3%.

Frequency response of pre-stressed structures with nonlinear cohesive interfaces

This paper explores two different methods to extract information about localized nonlinear shear cohesive behavior of interfaces from linear elastodynamic response. Both formulations are based on the concept of loading a cohesive interface statically into the nonlinear region and then superposing small amplitude vibrations or wave motions on the statically pre-loaded state. To a first order approximation the cohesive interface’s small amplitude dynamic behavior is assumed to be linearly compliant with the stiffness interpreted as the local slope of the cohesive law at the static pre-load level. The first investigation considers the vibrations of a beam made up of two sections partially bonded together through the depth of the beam to create a cracked interface. The dependence of the natural frequencies on the spring stiffnesses of a beam with the cracked interface replaced by bending and shear springs is calculated using first order beam theory. The dependence of the spring stiffnesses used in the vibration analysis on crack length, static pre-load, and yield stress of a Dugdale–Barenblatt cohesive zone in the interface is determined through a 2D elasto-static boundary element analysis of a cracked beam element, which treats the boundary nonlinearities directly. The second investigation concerns the dispersion relations for time-harmonic guided waves in a layer connected to a rigid substrate by a very thin interface layer of material with nonlinear and softening behavior. The interfacial spring stiffness which, is directly included in the dynamic layer boundary conditions, is again interpreted as the local slope of the cohesive law at the static pre-load level. The spring stiffnesses inferred from the dispersion relations of either SH or generalized Rayleigh–Lamb waves from a series of measurements taken at multiple pre-load levels could then be integrated to obtain the cohesive law.

Relationship between pre-compaction stress and shear strength under confined and semi-confined loadings for a sandy loam soil

Mechanical soil strength is typically measured in terms of the maximum normal pressure which can be applied before a substantial increase in soil compression occurs. This soil strength is termed pre-compaction stress (σpc) and is usually regarded as the stress at which the soil deformation changes from “elastic” behaviour to the “plastic and irreversible” case. It was hypothesised that the σpc is the point at which the shear stress generated by the applied mechanical forces is equal to the soil shear strength (τ). Therefore, the objectives of this research were (i) to determine the σpc values by both plate sinkage test (PST) and confined compression test (CCT); and the τ from shear box test on pre-compressed soil specimens and (ii) to obtain the relations between values of the σpc and τ of the same soil. Tests were conducted on the remoulded specimens of a sandy loam soil collected from the topsoil. Experiments were conducted at two gravimetric water contents: 17 and 19%. Preload stress ranged from 0 to 200 kPa. The centre section of the preloaded soil specimen was firstly submitted to a 49.6 mm PST; then immediately one cylindrical sample was cored for CCT and three separate samples were taken for the shear tests. The σpc prediction by PST was accurate, whereas the values obtained with CCT were 4.5 (for water content of 17%) and 8.5 (for water content of 19%) times higher than the nominal preload stresses. The results showed that there was a highly significant (R2 = 0.95**) linear relationship between the σpc values and the corresponding τ for both PST and CCT. Although there was a good relationship between the σpc and τ, the former was greater than the latter, indicating that shear deformation may occur in the zone that is theoretically believed to be reserved for elastic deformation. Therefore, it might be the case that σpc is not at a transition point between the small elastic deformations and the large plastic deformations, but it is located in a transition area where both types of deformation occur at the same time.

Stress Distribution after Installation of Fixed Frameworks with Marginal Gaps over Angled and Parallel Implants: A Photoelastic Analysis

The objective of this work was to compare by photoelastic analysis the stress distribution along a fixed framework placed over angled or parallel implants with different gap values between the framework and one of the implants. Two photoelastic models were created: (i) with parallel implants; (ii) with a 30 degrees angled central implant. In both cases, three implants were used, and CP titanium frameworks were constructed with commercial components. A plane polariscope was used to observe the photoelastic fringes generated after initial framework assembly, and also when an axial load of 100 N was applied over the central implant. For both models, stress analysis was conducted on well-fitting frameworks and on another with a 150 microm vertical gap between the framework and the central implant. The photoelastic analysis indicated that in the model with parallel implants, stress distribution followed the implant axis, and in the model with an angled implant, a higher and nonhomogeneous stress concentration was observed around the apical region of the lateral implants. The placement of an ill-fitting framework resulted in increased preload stress patterns. Stresses were generated after screw tightening of the frameworks, increasing when a load was applied and when a vertical gap was present. Angled implants resulted in oblique stress patterns, which were not transferred with homogeneity to the polymeric model.

Ultrasonic Stress Measurement: Application to Preload Assessment on Already Tightened Bolts

When a material is under mechanical load, the stresses modify the velocity of acoustic waves. This consists in acoustoelastic effect. This property can be exploited for stress measurement in the material itself when the stress concerns the surface of the material, or in the bulk material, as in bolts. The ultrasonic bolt tightening control allows knowledge of preload stress in screws. The accuracy is much better than in the case of torque wrench. In fact, the use of this mechanical-based measurement equipment leads to uncertainties due to random resistant torques, induced by mechanical manufacturing tolerances. The ultrasonic measurement of the pre-load gives the information about the tension inside of the bolt, independently of mechanical uncertainties. This consists in an in-situ measurement. More, in some cases, the ultrasonic method allows knowledge of the preload on bolts already tightened, without untightening. This method is called bi-wave method, and has many connections with birefringent method. Examples of application of the method are presented about the differential mode case, which is largely known and industrialized, and in the case of bi-wave method, which lead to several on site applications, performed by CETIM with a prototype equipment.

Effects of uniaxial prestress on the ferroelectric hysteretic response of soft PZT

This paper deals with the influence of preload stress on the ferroelectric hysteretic behavior of piezoelectric ceramics. The polarization and strain versus electric field hysteresis loops were measured for soft lead zirconate titanate (PZT) piezoceramic material under various uniaxial compressive stress preloads of up to −400 MPa. The investigation revealed that the superimposed compression load reduced the remnant polarization, decreased the coercive field, and also had a significant impact on the dielectric and piezoelectric properties. With increasing mechanical load, dielectric hysteresis and butterfly hysteresis became less and less pronounced, as the compressive stress prevented full alignment of the domains and induced mechanical depolarization. The slopes of the polarization and strain curves at zero electric field were measured to evaluate the dependence of permittivity and piezoelectric coefficients on the prestress. The experimental results were interpreted in terms of the non-180° domain switching process under combined electromechanical loading.

Doppler-derived parameters of diastolic left ventricular function in preterm infants with a birth weight

Transmitral flow parameters in preterm and term infants were compared in order to study differences in signal expression and temporal dynamics of left ventricular diastolic function. In 63 preterm infants between 26 and 33 weeks of gestation and 102 term infants, a Doppler survey was performed during 6 months after birth. Early and atrial filling-time velocity integrals and peak velocities were significantly lower in the preterm neonates. Atrial filling parameters reached the level observed in term infants by 2 months of age. Peak early filling velocity was still lower for 2-month-old preterms and attained the term infants' level by 3 months of age. Preterm infants continued having high atrial filling fraction (AFF) (0.51±0.07) during 2 months after birth, while in term infants the fraction decreased continuously from 0.41±0.06 to 0.37±0.05. Isovolumic relaxation time (IVRT) was the only parameter without differences between preterm and term infants, and it decreased from 54±7 ms in neonates to 41±4 ms over 3 months. Stroke volume passing the mitral valve doubled in preterm (4±1 to 7.9±1.5 ml/cm 2), but increased by only 37% (6.9±1.6 to 9.5±2.2 ml/cm 2) in term infants. Our observations show that the maturational period of diastolic function appears prolonged in preterm infants. As preterm infants have to cope with a higher physiologic preload augmentation during growth, part of the delay in parameter changes might be caused by preload stress rather than by persistence of functional impairment. Although doing well under physiological conditions, preterm neonates may be at higher risk for diastolic dysfunction than term infants when an additional preload challenge is encountered.

Inhaled nitric oxide modifies left ventricular diastolic stress in the presence of vasoactive agents in heart failure.

Nitric oxide (NO) inhalation therapy has been widely used in several diseases with pulmonary hypertension. However, application of NO inhalation therapy remains controversial in heart failure. Cardiovascular effects of inhaled NO (iNO) were evaluated in dogs before and after induction of heart failure with and without infusion of vasoactive agents. iNO did not affect the baseline left ventricular (LV) function or the response to isoproterenol in control conditions or heart failure induced by procainamide. Pulmonary vascular resistance was significantly decreased by iNO in heart failure with infusion of vasoactive agents. Unexpectedly, LV end-diastolic pressure was significantly elevated by iNO in heart failure in the presence of infusion of vasoactive agents independent of their types; either the vasodilating agents of acetylcholine and nitroglycerin or the vasoconstricting agents of norepinephrine and angiotensin-II. The end-diastolic LV dimension and wall stress were also significantly increased by iNO, however, those at end systole were not affected. These results suggested that NO inhalation therapy reduced pulmonary vascular resistance, whereas in the presence of additional stress of vasoactive agents, it increased LV preload and end-diastolic wall stress in heart failure.

Selectivity of spontaneous rupture propagation on a branched fault

We simulated spontaneous dynamic rupture propagation on a branched fault system using the boundary integral equation method (BIEM) in 3D homogeneous, unbounded elastic medium. From the numerical experiments, we found that slightly heterogeneous preload stress field on the branches caused selective rupture propagation. Dynamic rupture propagation spontaneously on both branches requires very delicate conditions for the initial stress field as well as for the fracture criterion on them.

Bone response to implant-supported frameworks with differing degrees of misfit preload: in vivo study in rabbits.

To study the bone response around implants placed in tibia of rabbits that supported misfitting superstructures secured with different degrees of preload. Twelve rabbits were provided with two terminal 10-mm and one intermediate 7-mm-long implant in each tibia. After an integration time of about 9 weeks, nine of the animals received one control framework each (n = 9), designed with good fit to all three implants. In the other tibia of these animals, and in both tibias in the remaining three rabbits, test frameworks (n = 15) were connected with a vertical misfit of about 1 mm to the intermediate implant. The intermediate set screws were tightened with a torque ranging from 15 Ncm to 26 Ncm in the different test frameworks. The fascia and skin was then sutured back over the implants. After a loading period of 2 to 3 weeks, the animals were sacrificed, and histomorphometric measurements were made and correlated to the different levels of preload of the central implant. The mean bone-to-metal contact for the three best consecutive threads of the central implant was 40% for both test and control sites (p > .05). Compared to the other regions of the implant thread, less bone-to-metal contact was found at the tip of the test implant threads in the low preload group (p < .05). However, the same relation was not observed in the high preload group. A significant correlation was observed between increasing degree of preload in the central screw joint and increasing bone-to-metal contact, most obviously noticed at the tip of the implant thread (p < .01). Misfit stress levels of clinical magnitudes do not seem to jeopardize osseointegration per se. On the contrary, clinical levels of preload stress seem to significantly promote bone remodeling at the tip of the implant thread.

Hemodynamic responses to dobutamine during acute normovolemic hemodilution

The effects of dobutamine (DOB) on myocardial performance, systemic hemodynamics, and oxygen delivery during acute normovolemic hemodilution in anesthetized rats were studied. Forty-two Sprague Dawley rats (body weight 375 to 425 g) were divided into six equal groups. Hemodynamic and cardiac indices were measured or calculated at baseline, 30 minutes after the initiation of hemodilution (HD), and 15 minutes after DOB or saline infusion. Myocardial performance in response to acute pressure or volume loads was studied in all groups of animals. HD to a hematocrit (Hct) value of 20% resulted in no change in heart rate (HR), increased CI, SVI, and LV dP/dt, and decreased MAP, SVRI, and oxygen delivery index (O 2DI). HD increased peak SV and Cl after preload stress while the left ventricular developed pressure (LVDP) was unchanged. Infusion of DOB as 7.5 or 15 μg/kg/min increased HR, CI, and LV dP/dt as well as LVDP. At the same time, DOB decreased MAP and SVR, whereas the SVI remained unchanged. In non-HD animals both doses of DOB increased LVDP, but only the larger dose increased CI, whereas peak SV decreased with the smaller dose. Arterial carbon dioxide tension (PaCO 2) increased, whereas pH and arterial oxygen tension (PaO 2) decreased; however, O 2DI remained unchanged. Concomitant hemodilution and DOB infusion resulted in attenuation of HR response to DOB, exaggerated the drop in MAP and SVR, and increased LV dP/ dt. Only the larger dose of DOB increased the CI, whereas neither dose could alter the SVI in HD animals. Whereas HD increased the peak CI and SVI, administration of DOB to HD animals did not change LVDP, peak Cl, or peak SVI. Administration of DOB to HD animals decreased pH and increased PaCO 2)but O 2DI was not changed. The study demonstrated that the use of DOB to increase the physiologic compensatory mechanisms induced by HD was not effective, and the hemodynamic profile of DOB obtained in HD rats was significantly different from that observed in the non-HD groups. Therefore, it could be suggested that in normovolemic HD, DOB may fail to increase myocardial performance against sudden increase in afterload or preload although DOB can increase the CI in the resting or unstressed state.

Circulatory Effects of Verapamil During Normovolemic Hemodilution in Anesthetized Rats

Patients who have undergone perioperative normovolemic hemodilution may require calcium channel blockers for the treatment of myocardial ischemia and/or supraventricular tachyarrhythmias. The purpose of this rodent study was to examine the effect of intravenous verapamil on the hyperdynamic circulatory response to acute normovolemic hemodilution (hematocrit 20%). Anesthetized animals were randomly divided into four groups equal in number: (1) controls (no hemodilution, no drug); (2) hemodilution only; (3) verapamil only; and (4) hemodilution followed by verapamil. Cardiac output was recorded using an electromagnetic flow probe. Pre- and afterload tests were performed, the former consisting of rapid infusion of blood adjusted for hematocrit, the latter consisting of an aortic clamp technique. Animals in group 2 had significantly (P less than 0.05) greater percent increases in cardiac index, stroke volume index, and dP/dt, and greater percent decreases in mean arterial pressure, systemic vascular resistance, and oxygen delivery than did control animals (group 1). Infusion of verapamil after hemodilution (group 4) did not interfere with the compensatory increases in cardiac index and stroke volume index seen in group 2, nor did it reduce the peak stroke volume index in response to preload stress, although it did reduce resting dP/dt, mean arterial pressure and systemic vascular resistance, and peak cardiac index and "left ventricular developed pressure" after preload and afterload stress, respectively. We conclude that reduced ventricular function after verapamil administration does not interfere with the compensatory increase in stroke volume index after normovolemic hemodilution.