Differences In Stress Magnitudes Research Articles

Crop water stress index computation approaches and their sensitivity to soil water dynamics

There is a growing interest of using canopy temperature (Tc) based methods, including crop water stress index (CWSI), for irrigation management. However, different approaches exist to normalize Tc to microclimatic conditions, which can influence the accuracy and suitability of CWSI for irrigation scheduling. This study evaluated the performance of CWSI computation approaches and their sensitivity to changes in soil water depletion under different water stress levels. There were six different approaches – two empirical methods using developed lower baseline (i.e., CWSI-EB1, CWSI-EB2), two empirical methods using either artificial (CWSI-EA) or actual/natural (CWSI-EN) canopy reference surfaces, and two theoretical approaches which differ by how aerodynamic and canopy resistances are determined (CWSI-Th1, CWSI-Th2). Stationary infrared thermometers (IRTs) provided continuous Tc to calculate CWSI-EB, CWSI-Th, and CWSI-EN; whereas mobile IRTs and a thermal camera provided one-point-in-time Tc and temperatures of artificial canopy reference surfaces to calculate CWSI-EA. These measurements were all collected from full and deficit irrigated and rainfed maize plots in West Central Nebraska. Day-to-day variations within and across CWSI approaches were evident and their sensitivity to soil water depletion varied. Greater sensitivity and correlation strength to depletion (Dr,i) were observed with CWSI-Th and CWSI-EB under severe stress (i.e., Dr,i > 80%) at deeper soil depths of 1.8 and 2.1 m, producing r2 which ranged from 0.61 to 0.80 (slope: 0.03–0.05) and 0.69–0.79 (slope: 0.03–0.04), respectively. Observed differences in stress magnitudes among approaches and treatments, warrants a specific irrigation triggering threshold for each approach. Additionally, developing a robust index coupling both CWSI and soil water depletion is desirable to improve irrigation water management by accounting for both soil and plant water status.

True colours or red herrings?: colour maps for finite-element analysis in palaeontological studies to enhance interpretation and accessibility.

Accessibility is a key aspect for the presentation of research data. In palaeontology, new data is routinely obtained with computational techniques, such as finite-element analysis (FEA). FEA is used to calculate stress and deformation in objects when subjected to external forces. Results are displayed using contour plots in which colour information is used to convey the underlying biomechanical data. The Rainbow colour map is nearly exclusively used for these contour plots in palaeontological studies. However, numerous studies in other disciplines have shown the Rainbow map to be problematic due to uneven colour representation and its inaccessibility for those with colour vision deficiencies. Here, different colour maps were tested for their accuracy in representing values of FEA models. Differences in stress magnitudes (ΔS) and colour values (ΔE) of subsequent points from the FEA models were compared and their correlation was used as a measure of accuracy. The results confirm that the Rainbow colour map is not well suited to represent the underlying stress distribution of FEA models with other colour maps showing a higher discriminative power. As the performance of the colour maps varied with tested scenarios/stress types, it is recommended to use different colour maps for specific purposes.

Carbon fiber-reinforced PEEK in implant dentistry: A scoping review on the finite element method

Objective : The aim of the present study was to perform an integrative systematic review on the stress distribution assessed by finite element analysis on dental implants or abutments composed of carbon fiber-reinforced PEEK composites. Method: An electronic search was performed on PUBMED and ScienceDirect using a combination of the following search terms: PEEK, Polyetheretherketone, FEA, FEM, Finite element, Stress, Dental implant and Dental abutment. Results: The findings reported mechanical properties and the stress distribution through implant and abutment composed of PEEK and its fiber-reinforced composites. Unfilled PEEK revealed low values of elastic modulus and strength that negatively affected the stress distribution through the abutment and implant towards to the bone tisues. The incorporation of 30% carbon fibers increased the elastic modulus and strength of the PEEK-matrix composites although some studies reported no statistic differences in stress magnitude when compared to unfilled PEEK. However, an increase in short carbon fibers up to 60% revealed an enhancement on the stress distribution through abutment and implants towards to the bone tissues. PEEK veneering onto titanium core structures can also be a strategy to control the stress distribution at the implant-to-bone interface. Conclusions: The stiffness and strength of PEEK-matrix composites can be increased by the improvement of the carbon fibers’ network. Thus, the content, shape, dimensions, and chemical composition of fibers are key factors to improve the stress distribution through abutment and implants composed of PEEK-matrix composites.

Mapping Stresses on the Tibial Plateau Cartilage in an Ovine Model Using In-Vivo Gait Kinematics.

Understanding stresses within the knee joint is central to understanding knee function, and the etiology and progression of degenerative joint diseases such as post-traumatic osteoarthritis. In this study, in vivo gait kinematics of four ovine subjects were recorded using a highly accurate Instrumented Spatial Linkage (ISL) as each subject walked on a standard treadmill. The subjects were then sacrificed, and the right hind limbs removed. Ten purpose-built Fibre Bragg Grating (FBG) sensors were positioned within each stifle joint and used to measured contact stresses on the articulating surface of the tibial plateau as the recorded gait was replicated using a 6-degrees-of-freedom parallel robotic system. This study provides the first accurate, direct measurement of stress in a joint during in vivo gait replication. It was hypothesized that the results would indicate a direct link between gait kinematics and measured stress values. Contrary to this expectation no direct link was found between individualistic differences in kinematics and differences in stress magnitudes. This finding highlights the complex multifactorial nature of stress magnitudes and distribution patterns across articular joints. The results also indicate that stress magnitudes within the knee joint are highly position dependent with magnitudes varying substantially between points only a few mm apart.

Comparative study on stress analysis in human molar tooth between metallic and nonmetallic dental filling material

Dental filling is regarded as proven dental restoration method in dealing with partial missing of tooth crown due to caries or trauma. This study analyses the reliability and durability of materials for dental filling using finite element analysis. Specifically, it determines the stress induced at a dental filling due to occlusal load. Two filling depths were simulated: (a) filling depth in enamel and (b) filling depth in enamel/dentine on top of molar tooth. Dental filling made of glass ionomer cement (GIC), composite, and amalgam (as a reference material) which represented metallic and non-metallic filling materials were chosen as the materials for this study. A 100 MPa pressure was applied on the dental filling to represent an occlusal load. The results obtained were the stress (magnitude and distribution) for enamel/amalgam, enamel/GIC, enamel/composite, enamel/dentine/amalgam, enamel/dentine/GIC, and enamel/dentine/composite. It was found that the maximum induced stress was higher for enamel/dentine depth while there is no significant difference in stress magnitude for all dental filling materials.

Modeling and simulations of transformation and twinning induced plasticity in advanced high strength austenitic steels

The current work is focused on the development of a combined micromechanical model of transformation and twinning induced plasticity in austenite based steels. Both mechanisms are combined by incorporating transformation in twinning based crystal plasticity model. Initially, mechanical twinning is incorporated in slip based crystal plasticity model. Afterwards, austenite to martensite transformation is included in the developed slip and twin based model. Kinematics of the mechanisms is developed by defining elastic, plastic, and transformation deformation gradients. Energy balanced principle is used to develop thermodynamic framework where dissipated energy and driving potential equations are formed. A fully implicit integration scheme is developed to solve constitutive equations. Numerical integration algorithm is then implemented in ABAQUS as a user-defined subroutine. Three dimensional finite element model of single and polycrystal austenite are developed. The orientation of each grain is defined through Euler angles. The performance of the model is evaluated through finite element simulations to predict elastic–plastic and transformation behaviors of single and polycrystal austenite. The developed model is in good agreement with the published experimental and simulation results. A prominent difference in stress magnitude is found once twinning mode is incorporated in slip and transformation. This difference has significant magnitude in case of polycrystal austenite. This shows substantial advantage in terms of strength and formability of incorporating mechanical twinning along with slip and transformation.

Quantitative Evaluation and Comparison of Stress Transmission Characteristics of Bar-Clip and Short Coping Overdenture Attachments Under Dynamic Loading: A Photoelastic Stress Analysis

When two canine abutment teeth are used to support an overdenture prosthesis, optimal stress distribution to minimize forces to abutments is desired. This study used photoelastic stress analysis to compare the stress patterns generated around canine abutments using two different overdenture retainer designs. Two canine abutments were anchored in the photoelastic mandible and overdentures were fabricated using two different overdenture attachments. The fitting surface of dentures were lined with resilient layer of light bodied silicon rubberbase impression material to simulate oral mucosa. The attachments used were Bar-Clip and Short coping type. Verticalload of 5 to 50 lb was applied by jaw simulator. Resultant stress fringes were photographed and evaluated quantitatively. Bar-Clip type of attachment transmitted more amount of stress than short coping type transmitted. There was gross difference in magnitude of stresses between two types of retainers. As the retentivity of the attachment increased there was more stress concentration around the abutments.

Prediction of damage and fatigue life of high-temperature flip chip assembly interconnections at operations

The determination of the real value of damage/plastic work density in solder joints from computer numerical modelling and its usage in fatigue life prediction models based on accumulated energy density is critical to improving the accuracy of predicted life of solder joints. Commercial ANSYS software based on three-dimensional finite element analysis (FEA) was employed to investigate damage of bonded materials of lead-free solder joints in a flip chip (FC48D6.3C457) mounted on a printed circuit board (PCB). The trend behaviour of accumulated damage and fatigue life per cycle over many accelerated thermal cycles (ATCs) are also studied. The solder bumps deformation is modelled using ANAND’s visco-plasticity and the performances of all other materials in the assembly were captured with appropriate material models. It was observed that the difference in stress magnitude and amplitude between inter-metallic compounds (IMCs) at the die side and solder bulk was highest and the presence of IMC in the joints increases bump damage which occurs in three stages during temperature cycle loading. These results demonstrate that while IMC impacts solder joint reliability, the bond at interconnect between IMC at the die side and solder bulk is most vulnerable to fatigue crack initiation and propagation. A new methodology to find accurate solder joint damage is presented. The findings show that average damage from cycle of hysteresis loop stabilisation to cycle of onset of tertiary damage demonstrates potential of being adequate in determining magnitude of the solder joint damage. However, considering that damage evolution is in three-phase, we propose the use of polynomial function to estimate plastic work damage in FC solder joints.

Tomographic particle image velocimetry investigation of the flow in a modeled human carotid artery bifurcation

Hemodynamic forces within the human carotid artery are well known to play a key role in the initiation and progression of vascular diseases such as atherosclerosis. The degree and extent of the disease largely depends on the prevailing three-dimensional flow structure and wall shear stress (WSS) distribution. This work presents tomographic PIV (Tomo-PIV) measurements of the flow structure and WSS in a physiologically accurate model of the human carotid artery bifurcation. The vascular geometry is reconstructed from patient-specific data and reproduced in a transparent flow phantom to demonstrate the feasibility of Tomo-PIV in a complex three-dimensional geometry. Tomographic reconstruction is performed with the multiplicative line-of-sight (MLOS) estimation and simultaneous multiplicative algebraic reconstruction (SMART) technique. The implemented methodology is validated by comparing the results with Stereo-PIV measurements in the same facility. Using a steady flow assumption, the measurement error and RMS uncertainty are directly inferred from the measured velocity field. It is shown that the measurement uncertainty increases for increasing light sheet thickness and increasing velocity gradients, which are largest near the vessel walls. For a typical volume depth of 6 mm (or 256 pixel), the analysis indicates that the velocity derived from 3D cross-correlation can be measured within ±2% of the maximum velocity (or ±0.2 pixel) near the center of the vessel and within ±5% (±0.6 pixel) near the vessel wall. The technique is then applied to acquire 3D-3C velocity field data at multiple axial locations within the carotid artery model, which are combined to yield the flow field and WSS in a volume of approximately 26 mm × 27 mm × 60 mm. Shear stress is computed from the velocity gradient tensor and a method for inferring the WSS distribution on the vessel wall is presented. The results indicate the presence of a complex and three-dimensional flow structure, with regions of flow separation and strong velocity gradients. The WSS distribution is markedly asymmetric confirming a complex swirling flow structure within the vessel. A comparison of the measured WSS with Stereo-PIV data returns an acceptable agreement with some differences in stress magnitude.

Comparative Feeding Biomechanics of Lystrosaurus and the Generalized Dicynodont Oudenodon

Differences in cranial morphology among the Dicynodontia have been correlated with changes in masticatory function, and hence, dietary preference. Although the derived masticatory apparatus of dicynodonts allowed propaliny, it has previously been hypothesized that Lystrosaurus primarily utilized powerful orthal jaw movements to process fibrous vegetation. Cranial specializations of Lystrosaurus, such as shortened and deepened cranium and a mobile premaxilla-nasal suture, are thought to have increased the efficiency of its masticatory system compared with generalized Permian dicynodonts. Here we aim to test this assertion using biomechanical modeling techniques. We use finite element analysis (FEA) and a study of cranial functional morphology to compare the biomechanical performance of the crania of Lystrosaurus and Oudenodon, a generalized dicynodont, during orthal bite simulations. Muscle forces were estimated for each dicynodont using the dry skull method and applied to each cranium to produce a reaction force at a bite point. Patterns and average magnitude of Von Mises stress in each dicynodont cranium and in segmented regions of interest were assessed. During orthal bite simulations, higher stress occurs throughout the Oudenodon cranium, indicating that the cranium of Lystrosaurus is more resistant to normal, static feeding loads. Despite this difference in stress magnitude, patterns of stress are similar within both taxa. The FE-stress results, along with mechanical advantage of adductor musculature, a broad symphyseal contact, and other cranial features suggest that Lystrosaurus may have used a snapping bite to cope with tough fibrous vegetation.

Effect of restoration type on the stress distribution of endodontically treated maxillary premolars; Three-dimensional finite element study

The purpose of this study was to investigate the effects of four restorative materials under various occlusal loading conditions on the stress distribution at the CEJ of buccal. palatal surface and central groove of occlusal surface of endodontically treated maxillary second premolar, using a 3D finte element analysis. A 3D finite element model of human maxillary second premolar was endodontically treated. After endodontic treatment, access cavity was filled with Amalgam, resin, ceramic or gold of different mechanical properties. A static 500N forces were applied at the buccal (Load-1) and palatal cusp (Load-2) and a static 170N forces were applied at the mesial marginal ridge and palatal cusp simultaneously as centric occlusion (Load-3). Under 3-type Loading condition, the value of tensile stress was analyzed after 4-type restoration at the CEJ of buccal and palatal surface and central groove of occlusal surface Excessive high tensile stresses were observed along the palatal CEJ in Load-1 case and buccal CEJ in Load-2 in all of the restorations. There was no difference in magnitude of stress in relation to the type of restorations. Heavy tensile stress concentrations were observed around the loading point and along the central groove of occlusal surface in all of the restorations. There was slight difference in magnitude of stress between different types of restorations. High tensile stress concentrations around the loading points were observed and there was no difference in magnitude of stress between different types of restorations in Load-3.

Kinematic development and paleostress analysis of the Denizli Basin (Western Turkey): implications of spatial variation of relative paleostress magnitudes and orientations

Paleostress orientations and relative paleostress magnitudes (stress ratios), determined by using the reduced stress concept, are used to improve the understanding of the kinematic characteristics of the Denizli Basin. Two different dominant extension directions were determined using fault-slip data and travertine fissure orientations. In addition to their stratigraphically coeval occurrence, the almost exact fit of the σ 2 and σ 3 orientations for the NE–SW and NW–SE extension directions in the Late Miocene to Recent units indicate that these two extension directions are a manifestation of stress permutations in the region and are contemporaneous. This relationship is also demonstrated by the presence of actively developing NE–SW and NW–SE elongated grabens developed as the result of NE–SW and NW–SE directed extension in the region. Moreover, stress ratios plots indicate the presence of a zone of major stress ratio changes that are attributed to the interference of graben systems in the region. It is concluded that the plotting of stress orientations and distribution of stress ratios is a useful tool for detecting major differences in stress magnitudes over an area, the boundaries of which may indicate important subsurface structures that cannot be observed on the surface.

Modelling the influence of tectonic compression on the in situ stress field with implications for seal integrity: the Haltenbanken area, offshore mid-Norway

Abstract Exploration for hydrocarbons in overpressured domains is often considered high risk because of the possibility of seal failure and fluid leakage due to natural hydraulic fracturing. Several of the wells drilled in highly overpressured reservoirs on Haltenbanken, offshore mid-Norway, have proved to be devoid of hydrocarbons suggesting that ineffective seals are the cause of exploration failure. However, recent petroleum discoveries within this area demonstrate that fluid pressure is not the ultimate control on entrapment of hydrocarbons. We investigate the way in which far-field tectonic compression may have influenced the in situ stress conditions on Haltenbanken, and assess whether tectonic stresses also may facilitate local fracturing of the seal by reducing the retention capacity (minimum horizontal stress-fluid pressure). We have approached the problem by applying a finite element model. The elasto-plastic model assumes two-dimensional plane-strain and is constrained from geological and geophysical data. The results show that: (1) contrasts in the rock’s mechanical properties across discontinuities (e.g. sediment interfaces) cause rapid shifts in stress magnitudes; (2) the differences in stress magnitudes across such discontinuities can be subdued or enhanced under increased horizontal compression; and (3) structurally controlled variations in vertical displacements produce local concentrations of highs and lows in the stress field. The combined result of these three factors is that the magnitude of horizontal stress may vary quite considerably within spatially restricted areas. The implication of these predictions in terms of hydrocarbon preservation potential in highly overpressured regions is that rapid shifts in minimum horizontal stress magnitudes can reduce the retention capacity and therefore facilitate natural hydraulic fracturing.

Continuation of a deep borehole stress measurement profile near the San Andreas Fault: 2. Hydraulic fracturing stress measurements at Black Butte, Mojave Desert, California

Hydraulic fracturing stress measurements were obtained in the Black Butte drill hole, 18 km northeast of the San Andreas fault in the Mojave Desert, at depths from 251 to 635 m. In all tests the least and greatest horizontal principal stresses (Sh and SH, respectively) exceeded the vertical stress (Sν), indicating a thrust faulting stress regime. A single good‐quality hydraulic fracture impression from 309 m depth indicates an SH direction of N41°E ± 10°. This SH direction should be interpreted with caution because it is based on only one observation. This orientation is fairly compatible with nearby surface stress measurements but is incompatible with most of the hydraulic fracturing stress orientations reported from comparable depths in the Mojave Desert and is not favorable for right‐lateral slip on either the San Andreas fault or NW striking faults present farther to the east. The stress regime measured in the Black Butte hole is comparable to that measured at nearby shallow depths but differs from the strike‐slip or transitional (strike‐slip to thrust faulting) stress regime present at similar depths in two nearby holes: Crystallaire, 4 km northeast of fhe San Andreas fault, and Hi Vista, 32 km northeast of the San Andreas fault. The SH direction measured in these holes is approximately 60° counterclockwise of that observed in the Black Butte hole. The differences in stress magnitudes and orientation among these holes substantiate previous indications of local variations in stress in the upper kilometer of the crust in this area and cast doubt on the validity of linear elastic models in which the effects of the San Andreas fault dominate the stress field in the western Mojave Desert.

An analysis of stresses in a dental implant system

Successful replacement for missing teeth is one of the most complex problems facing the dental profession. Although many different types of dental implants are now available, their performance in restoring masticatory function is still limited and the subject of much controversy. Finite element stress analysis (FESA) has been used in the evaluation of existing dental implant design and offers the potential of evaluating and improving implant design without the risk and expense of implantation. A two-dimensional FESA was performed to study the effects that methods for trabecular bone representation and surgical positioning of the implant have on stresses around LTI carbon and aluminum oxide (Al 2O 3) dental implants. The results of this study have shown that modeling of individual cancellous bone trabeculae and modeling cancellous bone as a homogeneous material resulted in similar stress distributions; however, significant differences in stress magnitudes were observed. It was also observed that placement of the implant strongly influenced the state of stress in tissues surrounding it.

Development of a layered crenulation cleavage in mica schists of the Kanmantoo Group near Macclesfield, South Australia

Kanmantoo Group metasedimentary rocks are folded by a large, dextral, second-generation fold near Macclesfield, South Australia. In the hinge regions of this fold, pelitic schists are crenulated, which gives rise to a variably developed, layered, axial-plane crenulation cleavage. The layered cleavage is produced by different microstructural, mineralogical, and chemical changes on alternate limbs of asymmetric crenulations. The long limbs (mica or M domains) become enriched in muscovite at the expense of biotite, quartz, and feldspar with a consequent large increase of Al 2 O 3 and a smaller increase in K 2 O at the expense of SiO 2 , MgO, and FeO + Fe 2 O 3 . The compositional changes in the short limbs (quartz-feldspar or QF domains) are somewhat complementary, but comparison with uncrenulated rock within 20 mm of these crenulations shows that the layering development involves a bulk chemical change, primarily a depletion in MgO and FeO + Fe 2 O 3 . All mineral grains are finer and less equidimensional in M domains and coarser and more equidimensional in QF domains than in the equivalent uncrenulated rock. In addition, very little evidence of intracrystalline deformation, recovery, or partial re-crystallization was found in a wide range of variably intensely crenulated rocks. The crenulation cleavage probably developed by a combination of (1) rotation of existing grains accompanied by modification of their shape and size by diffusive processes, (2) migration of material, on the scale of grains and domains, controlled by the deformation path and microstructural anisotropies, and (3) nucleation and growth of grains with an orientation and shape compatible with the strain history in their vicinity during nucleation and growth. It is shown that a pressure solution mechanism driven solely by differences in stress magnitude will not explain the range of micro-structural and mineralogical changes. More important controls on diffusive mass transfer are likely to be available from the chemical reactions, strain history, volume changes, and microstructural anisotropies.