Stress Pulse Research Articles

A two-layer elastic strip under transverse impact loading: Analytical solution, finite element, and finite volume simulations

In this paper, wave propagation in a two-layer composite strip is investigated analytically and numerically. The strip is loaded by a very short transverse stress pulse. Three cases of the strip problem are assumed: (i) isotropic aluminum Al strip and two-layer strips made of (ii) Al and the ceramics Al2O3 and (iii) the ceramics Al2O3 and Al. The analytical method is based on Laplace and Fourier transform. The in-house finite element algorithm and thermodynamic consistent finite volume scheme are employed for computations, while the explicit time stepping procedure is used in both cases. The comparison of analytical and numerical results determines the degree of the accuracy of calculations, which is important for simulation of complex wave propagation problems in general heterogeneous media.

Influence of Temperature Pulse on a Nickel Microbeams under Couple Stress Theory

In this paper, the vibration of microbeams due to a temperature pulse has been investigated. The thermoelastic coupled equations for microbeam resonator have been derived via the modified theory of couple stress in connection with the generalized thermoelasticity with relaxation time. The analytical expressions for studied fields due to modified couple stress for the microbeam have been obtained by applying the Laplace transform method. In addition, some comparisons have been displayed in graphs to estimate the effects of different parameters such as the couple stress parameter and pulse of temperature on the considered fields. Numerical conclusions demonstrate that the estimation of deflection expected by the new theory is lower than that of the classical one. Comparisons are made with the results of different models in the absence and presence of couple stress theory. Particular cases of interest are also derived.

The transient intrusion effect of high energy fluid on the rock failure around the wellbore during the dynamic stimulation process

Dynamic wellbore stimulation technologies, such as high-energy gas fracturing, electrical pulse fracturing, hydraulic pulsation fracturing, are generally designed to multi-fracture the near-wellbore region through generating high energy pulse with intermediate or high loading rate. During the stimulating process, the dynamic strength and failure mode of saturated rocks around the wellbore can be largely affected by the transient intrusion of high energy fluid. Accordingly, an experimental method was developed to provide a method to apply the tailored pulse loading in the central borehole of the cylindrical rock samples. Three groups (Saturated + Center hole exposed (S-CHE), Saturated + Center hole wall isolated (S-CHI), Dry + Center hole wall isolated (D-CHI)) tests were carried out. The borehole fluid pressure-time curves and the failure modes of rock samples were tracked, analyzed and compared for all of the experiments. Experimental results demonstrate that: The relationship between rock dynamic strength and loading rate is monotonic direct proportionality. The dynamic strength of saturated rock shows a much stronger strain rate dependence than that of the dry rock. At the same loading rate, fluid penetration can largely weaken the dynamic strength of rock samples. The stress pulse generates a complex crushed zone around the wellbore, while the fluid penetration tends to produce radial multi-fractures. These phenomenons were explained using the micromechanics-based macroscopic damage theory, which is capable of obtaining the relationship between the fluid intrusion and the fracture deformation in the rock dynamic failure process.

Mechanistic Modeling and Economic Analysis of Piezoelectric Energy Harvesting Potential in Airport Pavements

This study investigated the feasibility of applying piezoelectric energy harvesting technology in airfield pavements through mechanistic modeling and economic analysis. The energy harvesting performance of piezoelectric transducers was evaluated based on mechanical energy induced by multi-wheel aircraft loading on flexible airfield pavements. A three-dimensional finite element model was used to estimate the stress pulse and magnitude under moving aircraft tire loading. A stack piezoelectric transducer design was used to estimate the power output of a piezoelectric harvester embedded at different locations and depths in the pavement. The aircraft load and speed were found to be vital factors affecting the power output, along with the installation depth and horizontal locations of the energy harvester. On the other hand, the installation of the energy module had a negligible influence on the horizontal tensile strains at the bottom of the asphalt layer and compressive strains on the top of the subgrade. However, the near-surface pavement strains increased when the edge ribs of the tire were loaded on the energy module. Feasibility analysis results showed that the calculated levelized cost of electricity was high in general, although it varies depending on the airport traffic levels and the service life of the energy module. With the development of piezoelectric materials and technology, further evaluation of energy harvesting applications at airports needs to be conducted.

Concrete density estimation of linac bunker walls using impact-echo testing.

To estimate the concrete density of a newly constructed bunker using impact-echo testing prior to the installation of the linear accelerator. A newly constructed bunker showed visible honeycombing after the removal of the construction formwork. Impact-echo testing, which is based on the propagation and reflection of elastic waves in solids, was applied to confirm the bunker shielding integrity. A mechanical impact on the bunker wall generates a stress pulse, which propagates through the wall and is reflected or refracted by voids or changes in material characteristics such as density. Surface displacements caused by the reflected waves are recorded by a transducer, located near the impact point. The resulting displacement-time curves are analysed in the frequency domain for anomalies. The dominant frequencies are related to the depths from which stress waves are reflected within the structure. If the dynamic elastic modulus and Poisson ratio of the concrete are known, then the measured velocity of the so-called P-wave can be related to the concrete density. Validation measurements on a wall with known concrete density gave an estimate within 3% of the true density. Measured velocities on the honeycombed wall ranged from 3750m/s to 4300m/s, corresponding to densities of 2894kg/m3 and 2201kg/m3 respectively, with the majority of estimated densities ranging from 2307kg/m3 to 2544kg/m3. A radiation survey after the installation of the linear accelerator confirmed adequate shielding. Impact-echo testing presents a viable solution to confirm bunker shielding integrity before the installation of a linac.

Electromagnetic Hopkinson bar: A powerful scientific instrument to study mechanical behavior of materials at high strain rates.

The split Hopkinson bar (SHB) has been widely used for testing the dynamic mechanical behavior of materials. However, it is hard to involve complex stress conditions in traditional SHB due to its intrinsic characteristics. The Electromagnetic Hopkinson bar (E-Hopkinson bar) has been recently proposed as a solution. Different from the traditional SHB, the stress pulse of the E-Hopkinson bar is generated directly by the electromagnetic force. Therefore, the stress pulse that loads the specimen can be accurately controlled. With this advantage, some experiments that cannot be done with traditional SHB can be conducted by the E-Hopkinson bar technique. In this review, we introduced briefly the basic principles of the E-Hopkinson bar. Some lasted tests, such as symmetrically dynamic compression/tension of materials, interlaminar fracture of composites, dynamic Bauschinger effect of metals, intermediate strain rate tests, and dynamic multi-axial tests were also introduced. This new technique will be helpful for those researchers in the field of solid mechanics, especially when the strain rate and complex stress condition are involved.

Investigation into the Body Diode Degradation of 6.5 kV SiC MOSFETs

The aim of this study is to investigate the main contributing factors to the degradation of the intrinsic body diode in SiC MOSFETs, caused by the expansion of stacking faults (SFs) from the substrate into the epitaxial layer, and how it affects their performance. Additionally, a comparison between DC forward current stress and surge current pulse stress is shown.

The Mechanical Response of Wet Volcanic Sand to Impact Loading, Effects of Water Content and Initial Compaction

The effects of water content and initial compaction on the dynamic response of volcanic sand from Mount Etna were investigated by a series of experiments on a long Split Hopkinson Pressure Bar apparatus capable of generating stress pulses of duration exceeding one millisecond. The dynamic stress–strain characteristics were determined until large final compressive strains were achieved. An experimental protocol for the preparation of samples characterised by different initial porosity and moisture content was defined in order to reproduce, in a laboratory environment, granular volcanic aggregates representative of naturally occurring soils in different initial density and water content states. It was found that, for limited amounts of water content, the dynamic response of the investigated volcanic wet sand is more compliant than in dry conditions. Conversely, highly saturated samples exhibit a steep increase in stiffness occurring at strains when the dynamic compressive behaviour becomes dominated by the response of the nearly incompressible water. The presence of water has negligible effect on the mechanical behaviour when the samples are loaded at quasi static strain rates. The grain size distribution and morphology of samples tested in different conditions were evaluated and compared by means of edge detection analysis techniques applied to high contrast images.

Electromechanical behaviors of soft and hard PZTs under different compressive stress pulses

In the present study, soft and hard PZTs discharge experiments under extrusion/impact were carried out to analyze the electromechanical behaviors under open and short circuit conditions. The results show that when subjected to extrusion, the soft PZT is more sensitive to stress, the hard PZT has higher discharge capacity under high-impedance (regard as open-circuit) condition, and the force-electric relationship of the two PZTs satisfy the traditional piezoelectric equation. Under impact, the open-circuit elastic compliance coefficient of two PZTs increases with the increase of stress, the maximum value is about 50 times of the quasi-static value, and the piezoelectric voltage coefficient is about 20% of the quasi-static value. The short-circuit elastic compliance coefficient of soft PZT is 10 times of the quasi-static coefficient, and the dynamic piezoelectric strain coefficient is 250% of the quasi-static coefficient. However, the dynamic stress-strain of hard PZT is nonlinear and the dynamic piezoelectric strain coefficient is 500 × 10−12 m/V, which is about double of the quasi-static constant.

A new model for the HPA axis explains dysregulation of stress hormones on the timescale of weeks.

Stress activates a complex network of hormones known as the hypothalamic–pituitary–adrenal (HPA) axis. The HPA axis is dysregulated in chronic stress and psychiatric disorders, but the origin of this dysregulation is unclear and cannot be explained by current HPA models. To address this, we developed a mathematical model for the HPA axis that incorporates changes in the total functional mass of the HPA hormone‐secreting glands. The mass changes are caused by HPA hormones which act as growth factors for the glands in the axis. We find that the HPA axis shows the property of dynamical compensation, where gland masses adjust over weeks to buffer variation in physiological parameters. These mass changes explain the experimental findings on dysregulation of cortisol and ACTH dynamics in alcoholism, anorexia, and postpartum. Dysregulation occurs for a wide range of parameters and is exacerbated by impaired glucocorticoid receptor (GR) feedback, providing an explanation for the implication of GR in mood disorders. These findings suggest that gland‐mass dynamics may play an important role in the pathophysiology of stress‐related disorders.

The effect of classical Turkish and Western music on university students' exam stress level, blood pressure and pulse rate: a randomized controlled trial

Introduction: Exam stress may cause anxiety, worry, emotion and condition changes in university students. Students use various methods to cope with exam stress. Music is a method used to cope with anxiety that reduces the stress level of individuals by creating a deep relaxation and providing a therapeutic environment. This research was carried out in a randomized controlled pre-test and post-test to examine the effect of regular Classical Turkish and Western music on university students’ exam stress level, blood pressure and pulse findings.Material and Method: The sample of the study consisted of 88 students (40 experiments, 48 controls) studying in different departments at this University between November 2017 and February 2018. Data were collected by exam anxiety scale and personal information form. The experiment group was played 25 minutes 4 days a week total 6 weeks and Classic Western and Classical Turkish music just before the exam. Examination anxiety scale was re-applied to the experimental and control groups just before the examination, and the vital sign findings of the students were examined.Findings: The mean score of the experimental group was 41.40±9.40 and the postest mean score was 23.20±4.16 and there was a statistically significant difference (p<0.01). In addition, diastolic, systolic blood pressure and pulse rate of the students in the group who listen to music were lower than those who did not listen to music. Conclusion: It has been determined that regular music performance is an effective method in reducing the stress levels and anxiety levels of the students.

Effects of crack closure and friction for linear crack under normal impact

This paper concerns the fracture mechanics problem for elastic cracked materials under transient dynamic loading. The nonlinear contact problem for a linear crack under normal impact loading is solved by the boundary integral equations in the frequency domain and the components of the solution are presented by the Fourier exponential series. The algorithm convergence is proved and the solution is obtained for different friction coefficients. The dynamic stress intensity factors are computed for different stress pulses and compared with those obtained neglecting the crack closure and friction.

A Systematic Method to Characterize the Soft-Failure Susceptibility of the I/Os on an Integrated Circuit Due to Electrostatic Discharge

In this paper, we present a methodology to characterize the I/O pins of a logic IC such as an application processor or ASIC with respect to soft-failure susceptibility due to electrostatic discharge. With the IC in a functional system, variable stress pulses are injected while the interface under test operates in real-world use cases. This test methodology enables the extraction of the IC behavior during ESD-like stress on a pin-by-pin basis. This characterization is intended to be performed during the validation stages of component development, making it possible to provide system developers with valuable information about potential modes of failure. This early detection of potential soft errors and their sensitivities can then be used to design for soft-failure robustness from the very beginning of system hardware and software design.

Effect of temperature on the impact ignition behavior of the aluminum/polytetrafluoroethylene reactive material under multiple pulse loading

An impact ignition experiment was conducted using a split Hopkinson pressure bar at 22, 65, 125, and 205 °C to study the ignition behavior of an aluminum/polytetrafluoroethylene reactive material under extreme conditions such as high temperature, pressure, and strain rate. The dynamic compression behavior, micromorphology, ignition threshold, ignition delay time, and failure characteristics of the aluminum/polytetrafluoroethylene reactive material were investigated. The results indicate that the material's sensitivity continuously increases with temperature. Moreover, three cases of ignition delay times (500–700, 1000–1100, and 1600–1700 μs) correspond to the time of the second, third, and fourth stress pulses, respectively. The combined results of scanning electron microscopy and high-speed photography show that the polytetrafluoroethylene fibers are stretched out due to their thermal softening at 125 °C, which in turn prevents the reactive material from being ignited at the third pulse. At 205 °C, the fractured specimen can be bonded between the bars by the remarkable polytetrafluoroethylene fibers, enabling the reactive material to be ignited at the third and fourth stress pulses. This study deepens our understanding of the impact ignition mechanism of aluminum/polytetrafluoroethylene reactive materials.

High-dynamic compressive and tensile strength of specimens made of cementitious materials

The strength of specimens made of cementitious materials increases with increasing loading rate. Herein, the model of Fischer et al. (CCR 58, 2014, 186–200) is revisited in the context of high-dynamic compression and extended to high-dynamic tension. The model is based on the assumptions (i) that cracking will start if the quasi-static material strength is reached, and (ii) that the high-dynamic strength gain refers to the increase of the stress during the failure process of the tested specimen. The model explains the behavior of cylindrical specimens made of dry cement paste, mortar, and concrete, subjected to high-dynamic compression. It also elucidates the performance of cylindrical specimens made of dry mortar and concrete, subjected to high-dynamic tension. It is concluded that the high-dynamic strength gain is a structural effect and that structures will be damaged if the dynamic stress exceeds the quasi-static strength, no matter how fast the stress is increased and how short the stress pulse lasts.

Research on a new laser path of laser shock process

In most laser shock process experiments, the traditional typical laser path is usually in use. However, the surface residual stress induced by laser shock process distribute unbalance. The residual stress released from the minimum axis, the effective of the laser shock process would lose. To solve it, a new laser path produced, the horizontal and vertical reciprocating (HVR). With the new path, the residual stress distribution unbalance reduced. The laser shock process efficiency improved. The traditional laser path induced stress unbalance produced by the time different between the laser pulse and stress pulse. The stress would overlay to the direction of the laser path, it’s the main reason that the material surface stress distribution unbalance. The laser pulse is 12–20 ns for most cases, but the stress pulse is 3 times of it. The results of the simulation shows the traditional laser path X axis stress is 25% larger than the Y axis, but the HVR path is nearly the same. The experiments of the results not only show the two laser path stress distribution different but also the laser shock area different affect the stress distribution. The laser path different affect stress distribution unbalance reason is because the overlay, and the laser shock area affect stress distribution different reason is the resilience.

The Effect of Stress Wave Interaction and Delay Timing on Blast-Induced Rock Damage and Fragmentation

Rock fragmentation by blasting is the most efficient way of rock breakage in hard rock mining applications. Fragmentation, as well as the properties of the fragments generated by the explosion, are of significant concern as the energy consumption at the mill is greatly affected by them. Dynamic loading of blasting generates a countless number of microcracks in the host rock, which despite the major cracks forming the fragments could not get enough time to coalesce and create macrocracks. These microstructures eventually impact the integrity of the intact rock and reduce its strength. Damage is considered as a scalar parameter, which accounts for the creation of flaws and microstructures in the rock, deteriorating its elasticity modulus. The stress waves and their interactions are the parameters that control damage around blastholes. In this study, using LS-DYNA numerical code, the effect of initiation timing on blast-induced rock damage and fragmentation is investigated. The results of the numerical models reveal the importance of the delays in damage as well as fragment size distribution. Delayed initiation provides enough timing for the cracks to grow, which preconditions the surrounding rock for the neighboring blasthole. The interaction between the stress waves resulting from the detonation of neighboring blastholes plays an important role in damage and fragmentation analysis. The optimum delay time can be obtained by considering the rise time and the duration of the stress pulse, the P and S wave travel times in the host rock, and the crack propagation time within the rock burden.

ОСОБЕННОСТИ КОНТАКТНОГО РАЗРУШЕНИЯ ЛЬДА

The formation of an intermediate layer under hydrostatic compression at a shear appearing due to the action of converging and diverging fronts of stress momentums (pulses) is considered. Continuous monitoring of deformational changes in the structure of ice was carried out using acoustic methods. The features of contact ice breaking in the diverging fronts of stress pulses are considered by the example of the slow impact of a rigid spherical indenter on an ice plate simulating half-space. Using the piezoelectric accelerometer, an oscillogram of the impact was recorded and a generalized dependence of the reduced stress on the reduced instantaneous velocity of the impact (semi-cubic parabola) was obtained. It is established that under conditions of the experiment (smooth convex indenter surface and icy half-space) a thin intermediate layer is formed, the properties of which determine the physical similarity in the family of curves «instantaneous force-instantaneous velocity». A rheological model with due regard for the change in the microstructure of ice during the impact is proposed. Quantitative determinations of the deformation changes in structure of solid ice samples were performed under intensive plastic deformation in a matrix with a profile similar to the Laval nozzle. The deformations created by the piston caused forced vibrations in the ice. The working surface of the piston in the form of an ellipsoid together with the smooth walls of the matrix and the reverse cone created conditions for parametric resonance and the formation of fronts of highfrequency stress pulses. Under influence of these pulses, zones with a superplastic fine-crystalline structure of ice (cumulative effect) were formed in ice. In the outlet cylindrical channel, a flow around an obstacle of the ice with the structure of an intermediate layer (dynamic viscosity 20 MPa s) and the distribution of velocities of motion over the channel cross section were studied. The obtained results can be used to simulate the processes of contact destruction of deep rocks by a support or an ice-resistant platform loaded with an ice field.

Minimum Required Distance of Strain Gauge from Specimen for Measuring Transmitted Signal in Split Hopkinson Pressure Bar Test

The minimum required distance of the strain gauge on the transmitted bar of the split Hopkinson bar has been determined from the position of a metallic specimen via an explicit finite element analysis. The minimum required distance was determined when the strain-time profiles at r = 0, 0.5Ro and 1.0Ro, were coincident (r is the radial position and Ro is the radius of the bar.). The determined minimum required distance, f(x), is presented as a function of the relative specimen diameter to that of the bar (x = D/D0): j(x) = - 0.9385.x3 + 0.6624.x2 - 0.7459.x + 1.4478 (0.1 ≤ x ≤ 0.9). This result demonstrates the Saint-Venant's principle of rapid dissipation of localized stress in transient loading. The result will be useful for the design/modification of the pseudo-one-dimensional impact instruments that utilise a stress pulse transmitted through the specimen. The result will also allow one to avoid unnecessarily remote strain gage position from the specimen.

Modelling of earthquake locations and source parameters in Kachchh region to understand genesis of earthquakes

Modelling of earthquake source locations and parameters infers seismogenesis of earthquakes. In this study, we modelled the earthquake source locations through hypocenter location algorithm using the difference in arrival time of P and S waves and source parameters through the Levenberg–Marquardt non-linear inversion method using S-wave spectra. A total of 340 aftershocks of 2001 Bhuj mainshock ( $$ 1.8 \le M_{w} < 4.3 $$ ), which have occurred in Kachchh, Gujarat, India from January 2014 to January 2015, are located in this study. Out of 340 aftershocks, digital waveforms of 78 aftershocks ( $$ 2.2 \le M_{w} < 3.9 $$ ) are used for estimation of the earthquake source parameters. The results obtained from earthquake locations show two clusters of seismicity along the Kachchh Mainland Fault (KMF) and North Wagad Fault (NWF) and three felt events ( $$ M_{w} \ge 3.0 $$ ); one along the Katrol Hill Fault (KHF) ( $$ M_{w} = 3.3 $$ ), two along the Banni Fault (BF) ( $$ M_{w} = 3.0,3.2 $$ ). The generation of these three felt events is attributed to the triggering mechanisms caused by the migration of fluids or the stress pulse generated by the 20 MPa stress drop of the Mw 7.7 Bhuj earthquake. A marked concentration of events is noticed in 15–30 km depth range, which could be attributed to the presence of a mafic intrusive body, resulting in stress build-up for earthquake generation in this region. The results of source parameters; seismic moment (M0), source radius (r) and stress drop (Δσ) vary from 1.86 × 1012 to 3.2 × 1015 N m, 146–262 m and 0.04–5.73 MPa, respectively. The maximum stress drop value is estimated to be 5.73 MPa at 24 km depth for the largest studied event of $$ M_{w} $$ 3.9. Large stress drops are confined to the 8–33 km depth range, which indicates the probable existence of the base of the seismogenic layer in this depth range. This observed large stress drops could be attributed to stresses induced by crustal mafic intrusive bodies and the presence of aqueous fluids in the lower crust below the region.