Numerical Investigation of the Fetal Left Heart Hemodynamics During Gestational Stages

Flow-driven hemodynamic forces on the cardiac tissues have critical importance, and have a significant role in the proper development of the heart. These mechanobiological mechanisms govern the cellular responses for the growth and remodeling of the heart, where the altered hemodynamic environment is believed to be a major factor that is leading to congenital heart defects (CHDs). In order to investigate the mechanobiological development of the normal and diseased hearts, identification of the blood flow patterns and wall shear stresses (WSS) on these tissues are required for an accurate hemodynamic assessment. In this study, we focus on the left heart hemodynamics of the human fetuses throughout the gestational stages. Computational fetal left heart models are created for the healthy fetuses using the ultrasound images at various gestational weeks. Realistic inflow boundary conditions are implemented in the models using the Doppler ultrasound measurements for resolving the specific blood flow waveforms in the mitral valve. Obtained results indicate that WSS and vorticity levels in the fetal left heart decrease with the development of the fetus. The maximum WSS around the mitral valve is determined around 36 Pa at the gestational week of 16. This maximum WSS decreases to 11 Pa at the gestational week of 27, indicating nearly three-times reduction in the peak shear stress. These findings reveal the highly dynamic nature of the left heart hemodynamics throughout the development of the human fetus and shed light into the relevance of hemodynamic environment and development of CHDs.

Fatigue Tolerance of Aged Asphalt Binders Modified with Softeners

Fatigue cracking caused by repeated heavy traffic loading is a critical distress in asphalt concrete pavements and is significantly affected by the selected binder. In recent years, the growing use of recycled asphalt materials has increased the need for the production of softer asphalt binder. Various modifiers/additives are marketed to adjust the grade and/or enhance the binder performance at high and low temperatures. The modifiers are expected to alter the rheological and chemical characteristics of binders and, therefore, their performance. In this study, the damage characteristics of modified and unmodified binders, at standard long-term and extended aging conditions, were tested using the linear amplitude sweep (LAS) test. Current data-interpretation methods for LAS measurements (including AASHTO TP 101-12, T 391-20, and recent literature) showed inconsistent results for modified binders. An alternative method to interpret LAS results was developed in this study. The method considers the data until peak shear-stress is reached because complex stress states and failure patterns are observed in the specimens after that point. The proposed parameter (Δ| G*|peak τ) quantifies the reduction in complex shear modulus measured at the peak shear-stress. The parameter successfully captures the effect of aging and modification of binders.

Photogrammetric Prediction of Rock Fracture Properties and Validation with Metric Shear Tests

An accurate understanding of jointed rock mass behavior is important in many applications ranging from deep geological disposal of nuclear waste, to deep mining, and to urban geoengineering projects. The roughness of rock fractures and the matching of the fracture surfaces are the key contributors to the shear strength of rock fractures. In this research, push shear tests with three normal stress levels of 3.6, 6.0, and 8.5 kPa were conducted on two granite samples with artificially induced well-matching tensile fractures with sizes of 500 mm × 250 mm and 1000 mm × 500 mm. The large sample reached on average a −60% weaker peak shear stress than the medium-sized sample, and a strong negative scale effect was observed in the peak shear strength. The roughness of the surfaces was measured using a profilometer and photogrammetry. The scale-corrected profilometer-based method (joint roughness coefficient, JRC) underestimates the peak friction angle for the medium-sized slabs by −27% for the medium sample and −9% for the large sample. The photogrammetry-based (Z′2) method produces an estimate with −7% (medium) and + 12% (large) errors. The photogrammetry-based Z′2 is an objective method that consistently produces usable estimates for the JRC and peak friction angle.

Introduction of a New Parameter to Quantify the Fatigue Damage in Asphalt Mastics and Asphalt Binder

This study involves the quantification of fatigue damage in asphalt materials by introducing a new fatigue damage parameter denoted as the F parameter. One waste filler, i.e., red mud and an asphalt binder were chosen to blend the asphalt mastics at three filler contents of 10, 20, and 30% respectively with respect to the volume of binder and tested at temperatures of 5, 15, and 25 °C. The proposed parameter incorporates the effect of both peak shear stress as well as the failure strain, and hence, can better represent the fatigue damage. A lower value of F is recommended for a better fatigue resistant material. The F parameter was found increasing with the increment in filler content, which signifies higher degree of damage with a high level of stiffening. On the other hand, it consistently decreased with the increment in temperature. The behavior of the materials under the action of increasing shear strain was clearly justified by using the F parameter corresponding to different filler contents and the testing temperatures. In addition to that, the observations from the F parameter were also complemented by the fatigue diagrams. Hence, the proposed parameter is envisaged to be a promising fatigue damage indicator in future works.

Prediction of Peak Friction Angle using Photogrammetry and Comparison to Shear Test Results of Metric Scale Rock Fractures

An accurate understanding of jointed rock mass behavior is important in many applications ranging from deep geological disposal of nuclear waste to deep mining to urban geoengineering projects. The roughness of rock fractures and the matching of the fracture surfaces are the key contributors to the shear strength of rock fractures. In this research, push shear tests with three normal stress levels of 3.6, 6.0, and 8.5 kPa were conducted with two granite samples with artificially induced well-matching tensile fractures with sizes of 500 mm × 250 mm and 1000 mm × 500 mm. The large sample reached on average a -60 % weaker peak shear stress than the medium-sized sample, and a strong negative scale effect was observed in the peak shear strength. The roughness of the surfaces was measured using a profilometer and photogrammetry. The scale-corrected profilometer-based method (JRC) underestimates the peak friction angle for the medium-sized slabs by -27 % for the medium sample and -9 % for the large sample. The photogrammetry-based (Z’2) method produces an estimate with -7% (medium) and +12 % (large) errors. The photogrammetry-based Z’2 is an objective method that consistently produces usable estimates for the JRC and peak friction angle.

Study on Failure Characteristics and Acoustic Emission Characteristics of Sandstone Under Variable Angle Shear

To study the shear damage and failure characteristics of red sandstone under different normal stress conditions, the failure process of sandstone under three different shear angles (50°, 55°, 60°) were studied by using variable angle shear test device. The shear stress-deformation curves and failure characteristics of sandstone were obtained, and the relationships between shear cracks and acoustic emission impact times, amplitude, peak frequency were established. With the increase of shear angle, the normal stress, shear stress and peak shear stress decrease gradually. The development of micro-cracks in the shear plane appear more earlier. The high frequency signal decreases significantly, which may have a significant corresponding relationship with the rock friction and shear effect. The failure mode of rock changes from plasticity to brittleness. The amplitude changes are concave, and more acoustic emission energy is released at compaction stage and plastic(failure) stage. The rock spalling mainly occur in the penetrating area of main and secondary cracks surrounding the two ends of specimen. The spalling degree was obviously weakened with the increase of shear angle. The results have important guiding value for judging and predicting the instability mechanism of rock engineering.

Numerical Analysis of Shear and Particle Crushing Characteristics in Ring Shear System Using the PFC2D

The shear and particle crushing characteristics of the failure plane (or shear surface) in catastrophic mass movements are examined with a ring shear apparatus, which is generally employed owing to its suitability for large deformations. Based on results of previous experiments on waste materials from abandoned mine deposits, we employed a simple numerical model based on ring shear testing using the particle flow code (PFC2D). We examined drainage, normal stress, and shear velocity dependent shear characteristics of landslide materials. For shear velocities of 0.1 and 100 mm/s and normal stress (NS) of 25 kPa, the numerical results are in good agreement with those obtained from experimental results. The difference between the experimental and numerical results of the residual shear stress was approximately 0.4 kPa for NS equal to 25 kPa and 0.9 kPa for NS equal to 100 kPa for both drained and undrained condition. In addition, we examined particle crushing effect during shearing using the frictional work concept in PFC. We calculated the work done by friction at both peak and residual shear stresses, and then used the results as crushing criteria in the numerical analysis. The frictional work at peak and the residual shear stresses was ranged from 303 kPa·s to 2579 kPa·s for given drainage and normal stress conditions. These results showed that clump particles were partially crushed at peak shear stress, and further particle crushing with respect to the production of finer in shearing was recorded at residual shear stress at the shearing plane.

Response spectrum-based seismic response of bridge embankments

A single degree of freedom model is presented for calculating the free-field seismic response of bridge embankments due to horizontal ground shaking using equivalent linear analysis and a design response spectrum. The shear wave velocity profile, base flexibility, 2D shape, and damping ratio of the embankment are accounted for in the model. A step-by-step procedure is presented for calculating the effective cyclic shear strain of the embankment, equivalent homogeneous shear modulus and damping ratio, fundamental period of vibration, peak crest acceleration, peak shear stress profile, peak shear strain profile, equivalent linear shear modulus profile, and peak relative displacement profile. Model calibration and verification of the proposed procedure is carried out with linear, equivalent linear, and nonlinear finite element analysis for embankments with fundamental periods of vibration between 0.1 and 1.0 s. The proposed model is simple, rational, and suitable for practical implementation using spreadsheets for a preliminary design phase of bridge embankments.

Effect of Different Bond Parameters on the Mechanical Properties of FRP and Concrete Interface

This paper presents double shear tests performed to investigate factors influencing the bond behavior between basalt fiber-reinforced polymer (BFRP), glass fiber-reinforced polymer (GFRP) laminate, and concrete blocks. In detail, thirty-six twin concrete blocks strengthened with the aforementioned FRP types were tested to evaluate the influence of FRP length, width, and thickness, and their bonding behavior. The 2D-DIC (digital image correlation) technique and several strain gauges bonded along the laminate were used to measure the strain distributions of the FRP-to-concrete interface. The failure mode, ultimate load, load–slip, strain distribution, and bond–slip relationships between the laminates and concrete were analyzed. Furthermore, bond–slip curves were compared with some other existing literature models. The results from the experiment showed that the ultimate load, peak bond stress, and slip increased with the increase in the BFRP and GFRP laminates length, width, and thickness. The values of peak shear stress and the corresponding maximum shear slip were significantly different because of the above-mentioned factors’ influence on them. The bond interface that contributes to the bearing of the shear load may grow to an extent and later shift from the loaded end when debonding progresses. Finally, the fractured surfaces of the failed FRP laminates were examined using scanning electron microscope (SEM), revealing that FRP rupture, debonding in concrete, and debonding in an adhesive–concrete interface were the main failure types.

Effects of Groove Feature on Shear Behavior of Steel-Sand Interface

Surface groove morphology of structure and particle distribution of soil had a significant effect on the surface friction of structure. In order to investigate the interface shear stress-shear displacement curves, interface model and interface shear strength index when normal stress, groove width, and groove angle change, the interface shear tests of standard sand with steel plates are performed using an improved direct shear apparatus. Test results indicate that the peak shear stress increases with normal stress and the intersection angle between groove direction and shear direction. When the angle increases by 45°, the peak shear stress increases range from 4% to 13%. The peak shear stress increases with groove width, for every 1 mm increase in groove width, and the increasing extent of peak shear stress ranges from 4% to 22%, 3% to 13%, and 1% to 6%, respectively. When the groove angle is 45° and 90°, the increasing extent of peak shear stress decreases with groove width, but when the groove angle is 0°, the decrease regularity of peak shear stress increasing extent is not obvious. The hyperbolic model and Gompertz-C model are used to study the shear stress-shear displacement curves of sand-steel interface. The ratio of the interface peak shear stress of the hyperbolic model and Gompertz-C model to that of the shear test ranges from 0.90 to 1.03 and 0.88 to 0.98, respectively. The interface friction angle at the sand-steel interface ranges from 22° to 29°, and the friction angle of the rough interface is larger than that of the smooth interface. The interface friction angle increases with the intersection angle between the groove direction and the shear direction, the largest at 90°, the second at 45°, and the smallest at 0°. Under the same groove angle, the interface friction angle increases with the groove width, for every 1 mm increase in groove width, and the increasing extent of interface friction angle ranges from 4% to 15%, 4% to 7%, and 2% to 3%, respectively. The increasing extent of interface friction angle decreases with groove width, and this change rule is more obvious at the groove angle of 45° and 90° than at 0°.