CREEP COMPLIANCE OF VISCOELASTIC MATERIALS AT CONSTANT TEPERATURE

Experiments were carried out to investigate the separate roles of the hydrostatic and deviatoric components of stress tensor (using the first and the second invariant and The results were expressed in term of stress dependent shear compliance in the time temperature region of the tests (up to seconds at of the Relaxation). was found to increase in magnitude with increasing both hydrostatic and deviatoric components of stress. caused a shift in the magnitude of and caused an increase in with time. The difference between the shear compliance in creep and recovery was found to decrease with and increase with . All the different effects mentioned above could be rationalized by the idea of the time dependent free volume. If the free volume increases with time by increasing this could explain the difference in the effect of and on and explain why creep is less than recovery

Structural solution of the horizontal joint of floor slabs in girderless frame

Despite the widespread use of monolithic construction, precast concrete remains in demand in the construction of residential and administrative buildings. Regardless of the advantages in technology and the quality of work, it is necessary and appropriate to modernize the existing design solutions, which allows you to simplify and speed up the technological operations during construction. Moreover, in the construction of complex nodes and joints, the qualification of workers is important, so simplifying the work without losing the quality of construction and ensuring strength, stability and durability is an important task. This problem can be solved by using modern embedded parts in the joints that do not require welding and other complex technological operations. In this paper, a constructive solution of the horizontal joint of the floor slabs located in the zone of action of minimal forces is proposed on the example of a girderless frame. The purpose of the study is to determine the stress-strain state of the proposed structural solution of the horizontal joint of floor slabs using loopshaped embedded parts «PFEIFER» and to develop recommendations for determining the shear compliance. Based on the analysis of the results of numerical modeling, the features of the stress-strain state of the joint during shear operation are revealed. The results obtained can be used in the design of buildings with precast-monolithic ringless frames, in the modernization of existing standard solutions of precast-monolithic frames, as well as other load-bearing systems made of precast concrete.

MECHANICAL PROPERTIES OF GRAIN CONTACTS IN UNCONSOLIDATED SANDS

Unconsolidated sands provide zones of high porosity and permeability important for freshwater aquifers, hydrocarbon production and CO2 sequestration. An understanding of the acoustics of unconsolidated sands enables the characterization of such formations using ultrasonics, borehole acoustics and seismic methods. Inversion of ultrasonic compressional and shear velocities measured for unloading as a function of confining pressure for room-dry unconsolidated sands allows information on the mechanical properties of the grain contacts to be obtained using an approach based on the divergence theorem. This allows the effective compliance of sand to be written as the sum of the compliance of the pores and of the grain contacts and does not assume that the grains are identical spheres, in contrast to previous approaches. Grain contacts are found to be more compliant under shear than under normal compression, and the ratio of the normal-to-shear compliance decreases with decreasing confining pressure, implying that the shear compliance increases faster with decreasing confining pressure than the normal compliance. This is of importance in understanding the role of shear in the failure of unconsolidated sands, such as occurs in shallow water flow, sanding and failure around injectors, where the change in stress is a function of the ratio of the normal-to-shear compliance ratio of the grain contacts.

Transcranial Focused Ultrasound Generates Skull-Conducted Shear Waves: Computational Model and Implications for Neuromodulation

ABSTRACTFocused ultrasound (FUS) is an established technique for non-invasive surgery and has recently attracted considerable attention as a potential method for non-invasive neuromodulation. While the pressure waves generated by FUS in this context have been extensively studied, the accompanying shear waves are often neglected due to the relatively high shear compliance of soft tissues. However, in bony structures such as the skull, acoustic pressure can also induce significant shear waves that could propagate outside the ultrasound focus. Here, we investigate wave propagation in the human cranium by means of a finite-element model that accounts for the anatomy, elasticity and viscoelasticity of the skull and brain. We show that, when a region on the frontal lobe is subjected to FUS, the skull acts as a wave guide for shear waves, resulting in their propagation to off-target structures such as the cochlea. This effect helps explain the off-target auditory responses observed during neuromodulation experiments and informs the development of mitigation and sham control strategies.

Intermolecular cross-correlations in the dielectric response of glycerol

We suggest a way to disentangle self- from cross-correlations in the dynamic susceptibility of the glass former glycerol by combining dielectric relaxation (BDS) with light scattering (DDLS), field cycling NMR, and shear compliance (SC) data.

Increasing contribution of grain boundary compliance to polycrystalline ice elasticity as temperature increases

ABSTRACTMeasured elastic stiffnesses of ice polycrystals decrease with increasing temperature due to a decrease in grain boundary stiffness with increasing temperature. In this paper, we represent grain boundaries as imperfectly bonded interfaces, across which traction is continuous, but displacement may be discontinuous. We express the additional compliance due to grain boundaries in terms of a second-rank and a fourth-rank tensor, which quantify the effect on elastic wave velocities of the orientation distribution as well as the normal and shear compliances of the grain boundaries. Measurement of the elastic stiffnesses allows determination of the components of these tensors. Application of the method to resonant ultrasound spectroscopy measurements made on ice polycrystals enables determination of the ratio BN/BS of the normal to shear compliance of the grain boundaries, which are found to be more compliant in shear than in compression. The ratio BN/BS is small at low temperatures, but increases as temperature increases, implying that the normal compliance increases relative to the shear compliance as temperature increases.

Mechanical Resonance Dispersion Revisited

Mechanical resonance dispersion is the inelastic response of a solid to a periodic shear stress. Instead of the elastic Young's Modulus, the phenomenon is described by both a real J', and an imaginary J'' component of complex shear compliance, corresponding to in phase and out of phase strain responses, respectively. The experimental results are plots of J' and J'' vs. frequency, which are typically in the audiofrequency range of 10 - 5600 Hz. Resonances are observed as maxima in J'' and inversions in J' at frequencies corresponding to modes of plastic deformation, which are much lower frequencies (audiofrequency range) than elastic normal modes. The theoretical explanation of Edwin R. Fitzgerald involves particle waves and momentum transfer and leads to a particle-in-a-box frequency formula for these inelastic modes. Unfortunately, most of his and other published raw data were never analyzed by this model. The purpose of this article is to apply this formula to previously uninterpreted resonance dispersion curves and to address some of the earlier criticism of Fitzgerald's work. Results of these calculations support the Fitzgerald Theory to a high degree, demonstrate the importance of impurities and chemical analysis, largely mollify previous criticisms, and suggest the possibility of a new particle wave mass spectroscopy at great distances.

Direction dependence of fracture compliance induced by slickensides

The effect of a fracture on seismic wave propagation can be represented in terms of the normal and shear fracture compliance. In many studies, fractures are assumed to have no preferential orientation for slip along the fracture plane. However, examination of fractures found in recovered cores or in exposed outcrops shows irregularities, such as hackles or slickensides, which are formed in the direction of joint/fault propagation. These irregularities, represented as sawtooth ridges, can be expected to facilitate movement in a particular direction more than the opposite direction, in a way that depends on the height and shape of the irregularities. As a result, fractured rocks should exhibit a different compliance for shear in one direction compared with shear in the opposite orientation. We used numerical modeling to offer a critical assessment of this phenomenon by directly calculating the change in normal and shear compliance in the presence of hackles. The effect of the geometry of the hackles, the friction coefficient between fracture surfaces, and the role of normal stresses on the ratio of normal-to-shear fracture compliance were evaluated.

Effect of Tow Meander on the Shear Compliance of Woven Engineering Fabrics Measured Using the Biaxial Bias Extension Test

In this paper, a non-orthogonal constitutive model [1] is used to investigate the effect of sample misalignment due to ‘tow meander’, across the initial blank sheet on the shear compliance of a woven glass fabric, as measured using the biaxial bias extension test with various transverse loads applied [2]. The same statistical distribution and spatial correlations of shear angles observed in the woven glass fabric have been automatically reproduced using ‘VarifabGA’ [3]. The effect of realistic tow directional variability is investigated by generating blanks using VarifabGA and then simulating the biaxial bias extension test using the finite element software, Abaqus ExplicitTM. In order to assign the initial fiber orientation to each element in the mesh, a unique element set is assigned to each element. A MatlabTM code 'InitialAngle.m' has been written to produce two input files; the first 'Mat.inp' includes the material property parameters of each element and the second 'Sec.inp' includes the sections of those elements. Finally, a comparison between the experimental and predicted shear compliance shows the effect of tow directional variabilityorientation to each element in the mesh, a method is introduced which involves assigning a unique element set to each element in the mesh. A Matlab code 'InitialAngle' has been written to produce two input files; the first input file 'Mat.inp' includes the material property parameters of each element and the second input file 'Sec.inp' includes the sections of those elements. Finally, a comparison between the experimental and predicted shear compliance shows the effect of tow misalignment on the shear compliance.

Modelling the Shear-Tension Coupling of Woven Engineering Fabrics

An approach to incorporate the coupling between the shear compliance and in-plane tension of woven engineering fabrics, in finite-element-based numerical simulations, is described. The method involves the use of multiple input curves that are selectively fed into a hypoelastic constitutive model that has been developed previously for engineering fabrics. The selection process is controlled by the current value of the in-plane strain along the two fibre directions using a simple algorithm. Model parameters are determined from actual experimental data, measured using the Biaxial Bias Extension test. An iterative process involving finite element simulations of the experimental test is used to normalise the test data for use in the code. Finally, the effectiveness of the method is evaluated and shown to provide qualitatively good predictions.