Stress Wave Speed Research Articles

Regional shear wave speeds track regional axial stress in nonuniformly loaded fibrous soft tissues

Ligaments and tendons undergo nonuniform deformation during movement. While deformations can be imaged, it remains challenging to use such information to infer regional tissue loading. Shear wave tensiometry is a promising noninvasive technique to gauge axial stress and is premised on a tensioned beam model. However, it is unknown whether tensiometry can predict regional stress in a nonuniformly loaded structure. The objectives of this study were to (1) determine whether regional shear wave speed tracks regional axial stress in nonuniformly loaded fibrous soft tissues, and (2) determine the sensitivity of regional axial stress and shear wave speed to nonuniform load distribution and fiber alignment. We created a representative set of 12,000 dynamic finite element models of a fibrous soft tissue with probabilistic variations in fiber alignment, stiffness, and aspect ratio. In each model, we applied a randomly selected nonuniform load distribution, and then excited a shear wave and tracked its regional propagation. We found that regional shear wave speed was an excellent predictor of the regional axial stress (RMSE = 0.57 MPa) and that the nature of the regional shear wave speed-stress relationship was consistent with a tensioned beam model (R2 = 0.99). Variations in nonuniform load distribution and fiber alignment did not substantially alter the wave speed-stress relationship, particularly at higher loads. Thus, these findings suggests that shear wave tensiometry could provide a quantitative estimate of regional tissue stress in ligaments and tendons.

A rate-dependent model and its user subroutine for cohesive element method to investigate propagation and branching behavior of dynamic brittle crack

Modeling the branching behavior of dynamic brittle crack helps reveal dynamic mechanism of brittle geomaterial fragmentation induced by multi crack bifurcation. In this study, the correlation between crack propagation speed and separation strain rate of crack surfaces is derived theoretically and verified based on the Kalthoff plate impact test, showing a strong linear positive proportional relationship. A rate-dependent constitutive law for cohesive element is proposed to predict the direction and branching of dynamic crack. The methodology of compiling the rate-dependent model for cohesive element via the user subroutine VUSDFLD is introduced. The sensitivity of element size, mesh structure, and material parameters to the dynamic branching model are discussed. Four models with different rate-dependent forms are compared with the previous numerical results to find the best one. It is found that the most superior constitutive relationship for cohesive element in modeling crack branching is the model in which only the maximum separation displacement is rate-dependent, and the traction strength keeps constant. As Young’s modulus increases, the position of the first large branching is advanced due to the increase of stress wave speed. The crack branching angle is positively correlated with fracture energy, which is speculated to be closely related to the geometrical nonlinearity of the tested plate and the redistribution of tensile stress. The appearance of fracture process zone of dynamic crack represented by the damage cohesive elements is investigated, based on which the branching mechanism and the number of crack branches are discussed. Unlike static crack, the fracture process zone of dynamic crack represented by the damage cohesive element zone shows a fan shape, of which the radius is also rate-dependent. The extent of the dynamic fracture process zone varies with the crack propagation speed, which controls the generation of subsequent crack branches and the instability of crack direction.

Comparison between static modulus of elasticity, non-destructive testing moduli of elasticity and stress-wave speed in white spruce and lodgepole pine wood

ABSTRACT Static bending tests to measure modulus of elasticity (MOEST) or wood stiffness provide an indicator of the structural performance of a finished product. These tests are however, slow and expensive. Tests to measure MOE using non-destructive testing (NDT) provide alternatives to MOEST tests; however, relationships between the different modes of measurement need to be established. Non-destructive testing MOE measured by two methods (SilviScan [MOESS] and time of flight [MOETOF]) have been compared with MOEST for lodgepole pine and white spruce. The relationships between stress wave speed (SWS) and MOEST have also been evaluated. Simple linear regressions of MOESS, MOETOF, and SWS had greater explanatory power (higher coefficients of determination (R2)) than did multiple linear regressions including growth rate or other wood fibre attributes. Simple linear regression from MOETOF and MOESS on MOEST had lower R2 for lodgepole pine than for white spruce; however, the converse was true for SWS. SWS had the highest R2 (89%) and MOESS the lowest R2 (47%) when regressed on MOEST in lodgepole pine. The results were tool and species specific, suggesting that R2 between MOEST and non-destructive testing MOE values must be validated separately for each commercial tree species and for each measurement technique.

Evaluation of Hugoniot parameters for unreacted Al/PTFE reactive materials by modified SHPB test

Numerical simulation is one of the most effective ways to investigate the internal damage mechanism for reactive materials (RMS), and an adequate equation of state (EOS) is of great importance. Explosives and lasers are widely employed to drive a flying plate to obtain the EOS parameters. However, the velocity achieved by these ways is too high to obtain the corresponding EOS parameters for unreacted RMS because they tend to be deflagrated under the intense dynamic loads. In order to evaluate the shock EOS parameters for unreacted Al/PTFE RMS, this work introduces a direct method based on the split Hopkinson pressure bar (SHPB) test. The traditional SHPB test was developed by adding two polyvinylidene fluoride piezoelectric sensors pasted at the bottom surfaces of cylindrical RM specimens, which could directly obtain the real-time stress wave speed, and the particle speed is tested by the strain gauge in the transmit bar. Therefore, the two key parameters (the elastic wave speed C0 and slope S) in the shock EOS are achieved by the method of directly linear fitting. This work could provide favorable reference for relative simulation researchers of RMS.

Relationship between the dynamic and static modulus of elasticity in standing trees and sawn lumbers of Paulownia fortune planted in Iran

This paper aims to introduce a relationship between the dynamic modulus of elasticity in healthy standing trees of Paulownia fortune (planted in Iran) and the static modulus of elasticity in sawn wood. For this reason, a stress-wave non-destructive testing technique was carried out in longitudinal and transverse directions in 14 trees into two diameter classes (25-31 cm and 32-38 cm) at breast height and in logs at different height of stem to measure the stress wave speed and consequently, dynamic modulus of elasticity. Then, static modulus of elasticity of samples was calculated using 3-point bending tests in the sawn wood. The results revealed that the stress-wave speed and dynamic modulus of elasticity in logs of paulownia are more than those of standing trees in longitudinal direction. Also, the diameter of the tree can significantly affect the stress wave velocity in standing trees and logs of paulownia. Finally, a high correlation coefficient exists between static modulus of elasticity and dynamic modulus of elasticity (r= 0.68) in this tree. Keywords: Modulus of elasticity, non-destructive testing, Paulownia, standing trees, stress-wave

On measuring the dynamic elastic modulus for metallic materials using stress wave loading techniques

Metallic materials are mostly rate dependent in mechanical behavior, but their elastic modulus under high strain rate is hard to measure accurately. In this paper, two methodologies are proposed based on stress wave theory in hope of accurate measurement for metallic materials, for example Ti6Al4V alloy. One is based on the one-dimension stress wave propagation in a long Ti6Al4V bar, and the elastic modulus under a high strain rate is obtained from the calculated stress wave speed. The other technique is to utilize the integrated Hopkinson pressure bar made of Ti6Al4V material. The obtained elastic moduli from these methods are compared and analyzed, and the results are consistent with each other. The numerical simulations with cylindrical and dogbone-shaped specimens are conducted to show the influence of bar indentation on measurement accuracy. An alternative method is introduced based on the vertical split Hopkinson pressure bar, which can extend the integrated Hopkinson pressure bar method for most metallic materials with small bulk. The verification experiments are also conducted. Finally, the limiting strain rate is estimated for potential measurement problems.

A novel surrogate lung material for impact studies: Development and testing procedures.

This work focuses on the development of a surrogate lung material (SLM) that reproduces the dynamic response of a human lung under various loading conditions and also allows for the analysis of the extent and distribution of damage. The SLM consists of polyurethane foam used to mimic the spongy lung tissue and fluid-filled gelatine microcapsules used to simulate the damage of alveoli. The bursting pressure of the microcapsules was investigated by conducting low and high rate compression tests on single microcapsules. A bursting pressure of around 5bar was measured which is comparable to the reported lung overpressure at injury level. Low and high rate compression tests were conducted on the SLMs. From the measured mechanical properties and mass density, the stress wave speed was calculated and found to be well in the range of the reported values for human lungs (16-70m/s). In order to study the extent and distribution of damage in the SLMs, as represented by burst microcapsules, a CT scan analysis was carried out before and after the impacts. The CT scan results clearly demonstrated the magnitude and distribution of damage within the specimen. The results are then compared to the Bowen curves, the most often used criteria for predicting blast injuries in humans. An excellent agreement was found between the observed damage in the surrogate lungs and the expected damage in real human lungs. In general, the SLM showed similar stress wave speed, bursting pressure and damage to that of the real lungs.

Cohesive element approach for dynamic crack propagation: Artificial compliance and mesh dependency

Zero thickness cohesive element approach for arbitrary crack propagation has a deficiency of introducing artificial compliance to the model, especially when cohesive elements are inserted into every element interfaces. For dynamic problems, the artificial compliance decreases the stress wave speed and makes the result less accurate. In this paper, the reason of the artificial compliance is examined, and the bilinear and exponential cohesive law are compared. The work shows that by choosing the right cohesive stiffness, element size and using bilinear cohesive law rather than exponential cohesive law, the artificial compliance issue can be limited to a negligible level without greatly increasing the computational time. Three numerical simulations are used to support the argument. The bilinear cohesive law also shows more robust behavior in terms of cyclic loading than exponential law, and a new cyclic loading formulation is proposed to help fix the discontinuity observed in exponential law. According to our finding, in order to limit the artificial compliance and computational time, large element size is recommended, however, in fracture problems, small element size around crack tip is essential to capture the cohesive zone behavior. To escape the dilemma, we modify the cohesive zone enlargement approach presented in the literature (Dugdale, 1960) and adopt it for arbitrary crack propagation. The modified methodology enlarges cohesive zone size by reducing the cohesive strength only around crack tips to allow more cohesive elements inside the cohesive zone. Two benchmark numerical simulations are carried out to verify the modified methodology.

Variation Characteristics of Stress Wave Speed for Anchorage System Under Instantaneous Excitation

Dynamic nondestructive testing is widely used to evaluate the bolt anchorage quality in an anchorage system. The consolidating wave speed, stress wave speed for anchorage system under instantaneous excitation, is a required parameter for the evaluation. However, it is very difficult to determine the wave speed since it is affected by many factors. In order to solve the problem, this paper tries to establish the relationships between consolidation wave speed and wave speed in anchorage medium. This paper used dynamic nondestructive testing for measuring consolidation wave speed and wave speed in anchorage medium through experiment. The consolidation wave speed is measured by the grouted bolts in concrete fabricated by casting the bolts within one cubic concrete block with the dimensions of (600 mm × 600 mm × 2400 mm) around steel bars, and the wave speed in anchorage medium is measured by concrete specimens. The results indicate that the consolidation wave speed ranges from wave speed in concrete to that in free steel bar, the consolidation wave speed and wave speed in concrete vary in exponential law, and that they are mutually symmetric. This proposes the new idea that wave speed in anchorage medium can be used to calculate consolidation wave speed, and this can make the evaluation of anchorage quality much easier and more accurate because the testing of wave speed in anchorage medium is well developed and reliable and it can be determined by only testing on standard cubic specimens (150 mm × 150 mm × 150 mm).

Mesoscale Modeling of Quartzite and Sandstone under Shock Loading: Influence of Porosity and Pressure-dependent Quartz Stiffness on Macroscopic Behavior

In this paper, quartzite and sandstone are numerically investigated under planar shock loading. Those geologic materials consist of cemented quartz grains. Quartzite has a compact structure whereas sandstone has a porosity of typically around 20%. A mesoscale (grain scale) model is developed in order to catch inter-granular interactions and porosity crushing under shock loading. For this purpose, quartz grains are explicitly resolved in a Finite-Element model such that their shape and orientation are represented. The quartz grains are modeled as elastic crystals with a pressure-dependent, anisotropic stiffness matrix. Using parameter variations, we study the effect of porosity and pressure-dependency of the quartz stiffness on the macroscopic behavior of quartzite and sandstone. Descriptors of the macroscopic behavior are macroscopic longitudinal stress and shock wave speed. These quantities are determined via a homogenization methodology.

G0510505 衝撃波による応力波の形成に関する研究([G051-05]流体工学部門一般セッション(5),流体工学部門)

In this paper interaction process between shock wave and solid is discussed. Such phenomenon is known to be one of the reasons of serious problem, such as the destruction of glass and structures by shock generated from supersonic plane, explosion and so on. In recent years, although the mechanism of interaction has been studied by many researchers, the details of process have not been known enough yet. In this study, the interaction phenomenon between a shock wave emitted from a diaphragmless shock tube and a solid block having different shape made of polycarbonate is experimentally visualized using Schlieren method. Strength of the impact force generated by shock impingement is evaluated by numerical simulation of the flow field using TVD scheme. As a result, stress wave is formed by the shock collision and propagates in the block and it is found that the shape and the propagation speed of stress wave depend on the shape and the material properties of block.

The Study of the Quantity of Wave Speed in Low Strain Integrity Testing of Foundation Pile

the stress wave speed is the necessary condition to make sure pile length and pile defects position in low strain integrity testing of foundation pile with the stress wave echo method. Quantifying the stress wave speed is very difficult, because it is affected by multi- factors. This has been choke point developing test technology of foundation pile. In the paper, some factors influencing the stress wave speed were analyzed according to stress wave theory and experiment results, the quantity relations of the stress wave speed in pile and time and concrete age were made sure. lastly, five brief methods to quantifying the stress wave speed in pile were presented to control pile quality for test engineers according engineering practice.

Analysis for Blade with Centrifugal Preload under the Impact Stress Wave

Foreign object damage of engine blades often occurs when they are working with high rotating speed. Nonlinear finite element models for foreign object damage of blades with different centrifugal prestress were established. And the initializations of stress and displacement field for blade due to centrifugal preload were obtained by the dynamic relaxation method in the beginning of the dynamic analysis of impact. The effect mechanism of centrifugal stress on the foreign object damage of the blade was also investigated based on the impact theory of prestressed Timoshenko beam and the principle of stress wave propagation. The results indicate that the local plastic deformation on the impact location of the blade with centrifugal preload, which is produced at the moment of impact, is decreasing with the increase of preload. Attenuation speed of compressive stress wave, which is produced by the moment of impact on the blade face, is reducing with the augment of preload.

Determining Modulus of Elasticity of Ancient Structural Timber

During maintenance of ancient timber architectures, it is important to determine mechanical properties of the wood component materials non-destructively and effectively, so that degraded members may be replaced or repaired to avoid structural failure. Experimental materials are four larch (Larix principis-rupprechtii Mayr.) components, which were taken down from the drum-tower of Zhengjue Temple of Yuanmingyuan (Old Summer Palace), Beijing, China. The larch components were cut into standard specimens first, and then stress wave transmission times, resistograph and densities were tested. Product of resitograph and stress wave speed squared is defined as modulus of stress-resistograph. Comparing with the modulus of elasticity (MOE) of the specimens tested by the traditional bending test method, it is found that there is a linear relationships between the modulus of stress-resistograph and modulus of elasticity (MOE), and the correlation coefficients are 0.7111. In order to better evaluate the modulus of elasticity (MOE) with the modulus of stress-resistograph, 95% confidence regression lines are suggested to be used for the future calculation.

OS09-3-3 Research on the Speed of Stress Wave with Digital Correlation Method

OS09-3-3 Research on the Speed of Stress Wave with Digital Correlation Method

OS09F122 Research on the Speed of Stress Wave with Digital Correlation Method

OS09F122 Research on the Speed of Stress Wave with Digital Correlation Method

MD simulation of a copper rod under thermal shock

In this paper, thermoelastic problem of one-dimensional copper rod under thermal shock is simulated using molecular dynamics method by adopting embedded atom method potential. The rod is on axis x, the left outermost surface of which is traction free and the right outermost surface is fixed. Free boundary condition is imposed on the outermost surfaces in direction y and z. The left and right ends of the rod are subjected to hot and cold baths, respectively. Temperature, displacement and stress distributions are obtained along the rod at different moments, which are shown to be limited in the mobile region, indicating that the heat propagation speed is limited rather than infinite. This is consistent with the prediction given by generalized thermoelastic theory. From simulation results we find that the speed of heat conduction is the same as the speed of thermal stress wave. In the present paper, the simulations are conducted using the large-scale atomic/molecular massively parallel simulator and completed visualization software.

Selection Efficiency for Solid Wood Traits in Pinus taeda using Time-of-Flight Acoustic and Micro-Drill Resistance Methods

Abstract Conventional sampling and laboratory analysis of solid wood properties to facilitate clonal screening in tree improvement programs are prohibitively time-consuming and expensive. Alternative methods—time-of-flight acoustics and micro-drilling resistance—were assessed for efficiency in screening clones for wood stiffness (modulus of elasticity [MOE]), strength (modulus of rupture [MOR]), and density. Ninety clones, consisting of 30 from each of 3 full-sib families, were screened in an 8-year-old loblolly pine (Pinus taeda L.) field test using a TreeSonic time-of-flight tool and Resistograph drill resistance tool. The same clones were sampled for wood specimens for laboratory tests of MOE, MOR, and density. TreeSonic stress wave speed measurements produced highly repeatable clonal phenotypes that facilitated efficient selection for MOE and to a lesser extent for MOR. Resistograph amplitude measurements had a strong genetic correlation with wood density and facilitated highly efficient selection for density, with correlated responses for MOR and MOE. Combining the indirect traits into a selection index improved gain for mechanical wood traits. Both tools provided high measurement rates that resulted in cost efficiencies. Indirect measurements of solid wood properties should be attractive for clonal selection programs that must screen thousands of clones under a finite budget.

Picosecond Pulsed Laser Induced Melting of Monocrystalline Copper: A Hybrid Simulation

A hybrid method combing molecular dynamics and two-step radiation heating model is used to study the kinetics and microscopic mechanisms of picosecond laser melting of monocrystalline copper in stress confinement regime. The nonequilibrium processes of laser melting are simulated by classical MD method, and laser excitation as well as subsequent relaxation of the conduction band electrons are described continually by two-step radiation heating model. The mechanism responsible for melting of copper under picosecond laser pulse irradiation can be attributed to homogeneous nucleation of the liquid phase inside the solid region. The speed of stress wave is predicted to be 4400m/s equal to that of sound. The liquid and crystal regions are identified definitely in the atomic configurations by means of Local Order Parameter, in-plane structure and number density of atoms. Velocity-reducing technique is proved efficient in avoiding the influence of the reflected stress wave on melting process by comparing two models with velocity-reducing technique and free boundary condition at the bottom respectively.

Analysis of Geometric Effects on Stress Wave Propagation in Epoxy Resins of Plate-Like Structure by Dynamic Photoelasticity Combined with Strain Gauge

Experimental studies have been conducted using the dynamic photoelastic technique combined with a strain gauge to investigate geometric effects on stress wave propagation in axially impacted epoxy resins of plate-like structure. Dynamic photoelasticity provides a means of visualizing the stress wave field inside a solid. A device that triggers the generation of stress waves by direct projectile impact is used to conduct high-speed photoelasticity and strain gauge measurements. This triggering is achieved by an electrical connection between projectile and sample. The geometric effects of the width-to-wavelength ratio on the propagation speed and attenuation coefficient of stress waves were analyzed for isotropic rectangular rods of different width-to-thickness ratios, the thickness being the same in each case. The experimental results for stress wave speed as a function of width-to-wavelength ratio are in reasonable agreement with theoretical predictions based on a modified Love's equation involving the geometric effects due to lateral inertia.