Impact-induced tensile waves in a rubberlike material

This paper concerns the propagation of impact-generated tensile waves in a one-dimensional bar made of a rubberlike material. Because the stress-strain curve changes from concave to convex as the strain increases, the governing quasi-linear system of partial differential equations, though hyperbolic, fails to be genuinely nonlinear so that the standard form of the boundary-initial value problem corresponding to impact is not well-posed at all levels of loading. When the problem fails to be well-posed, it does so by exhibiting a massive loss of uniqueness, even though an entropy-like dissipation inequality is in force. Because the breakdown in uniqueness is reminiscent of a similar phenomenon that occurs in continuum-mechanical models for impact-induced phase transitions, a mathematically suitable, though physically unmotivated, supplementary selection mechanism for determining the solution naturally suggests itself. We describe in detail the solutions determined by two special forms of this selection mechanism, and we show that these two solutions provide bounds on the impact response, regardless of the selection principle used

On cavitation in Elastodynamics

Motivated by the works of Ball (1982) and Pericak-Spector and Spector (1988), we investigate singular solutions of the compressible nonlinear elastodynamics equations. These singular solutions contain discontinuities in the displacement field and can be seen as describing fracture or cavitation. We explore a definition of singular solution via approximating sequences of smooth functions. We use these approximating sequences to investigate the energy of such solutions, taking into account the energy needed to open a crack or hole. In particular, we find that the existence of singular solutions and the finiteness of their energy is strongly related to the behavior of the stress response function for infinite stretching, i.e. the material has to display a sufficient amount of softening. In this note we detail our findings in one space dimension

Thermo-Mechanical Wave Propagation In Shape Memory Alloy Rod With Phase Transformations

Many new applications of ferroelastic materials require a better understanding of their dynamics that often involve phase transformations. In such cases, an important prerequisite is the understanding of wave propagation caused by pulse-like loadings. In the present study, a mathematical model is developed to analyze the wave propagation process in shape memory alloy rods. The first order martensite transformations and associated thermo-mechanical coupling effects are accounted for by employing the modified Ginzburg-Landau-Devonshire theory. The Landau-type free energy function is employed to characterize different phases, while a Ginzburg term is introduced to account for energy contributions from phase boundaries. The effect of internal friction is represented by a Rayleigh dissipation term. The resulted nonlinear system of PDEs is reduced to a differential-algebraic system, and Chebyshev's collocation method is employed together with the backward differentiation method. A series of numerical experiments are performed. Wave propagations caused by impact loadings are analyzed for different initial temperatures. It is demonstrated that coupled waves will be induced in the material. Such waves will be dissipated and dispersed during the propagation process, and phase transformations in the material will complicate their propagation patterns. Finally, the influence of internal friction and capillary effects on the process of wave propagation is analyzed numerically.Comment: Keywords: nonlinear waves, thermo-mechanical coupling, martensite transformations, Ginzburg-Landau theory, Chebyshev collocation metho

How to characterize a nonlinear elastic material? A review on nonlinear constitutive parameters in isotropic finite elasticity

The mechanical response of a homogeneous isotropic linearly elastic material can be fully characterized by two physical constants, the Young’s modulus and the Poisson’s ratio, which can be derived by simple tensile experiments. Any other linear elastic parameter can be obtained from these two constants. By contrast, the physical responses of nonlinear elastic materials are generally described by parameters which are scalar functions of the deformation, and their particular choice is not always clear. Here, we review in a unified theoretical framework several nonlinear constitutive parameters, including the stretch modulus, the shear modulus, and the Poisson function, that are defined for homogeneous isotropic hyperelastic materials and are measurable under axial or shear experimental tests. These parameters represent changes in the material properties as the deformation progresses, and can be identified with their linear equivalent when the deformations are small. Universal relations between certain of these parameters are further established, and then used to quantify nonlinear elastic responses in several hyperelastic models for rubber, soft tissue, and foams. The general parameters identified here can also be viewed as a flexible basis for coupling elastic responses in multi-scale processes, where an open challenge is the transfer of meaningful information between scales

Preparation and characterization of natural rubber composites highly filled with brewers' spent grain/ground tire rubber hybrid reinforcement

Brewers' spent grain (BSG) and ground tire rubber (GTR) were applied as low-cost hybrid reinforcement natural rubber (NR). The impact of BSG/GTR ratio (in range: 100/0, 75/25, 50/50, 25/75 and 0/100 phr) on processing and performance properties of highly filled natural rubber composites was evaluated by oscillating disc rheometer, Fourier-transform infrared spectroscopy, thermogravimetric analysis, scanning electron microscopy, swelling behavior, tensile tests and impedance tube measurements. It was found that increasing content of GTR in NR/BSG/GTR composites accelerate cross-linking reactions during their preparation, which resulted in decrease of scorch time and optimal cure time. Simultaneously, higher content of GTR filler in NR/BSG/GTR composites significantly improved their physico-mechanical, thermal, morphological and acoustical properties. This indicates better compatibility between natural rubber matrix and GTR than with BSG, which is related to correlation between two factors. First factor is obvious differences in particles size and polarity of GTR and BSG, which affected physical interactions into phase boundary between NR matrix and BSG/GTR hybrid reinforcement. Second factor is possible migration of unreacted curing additives and carbon black particles from GTR filler to NR matrix, which played a significant role on processing and final properties of NR/BSG/GTR compositesPostprint (author's final draft

ENDOSCOPIC ULTRASOUND ACCESS DEVICE: THE THREE IN ONE COMPACT ERCP GAMECHANGER

Annually, more than 3,000 patients benefit from endoscopic retrograde cholangiopancreatography (ERCP) interventions to diagnose and treat conditions affecting the pancreaticobiliary ducts. However, the persistent lack of specialized ERCP cannulation devices elevates the risk of patient complications and procedure failure. Boston Scientific's development of a EUS access ERCP specialized catheter delivers a gamechanger that shortens procedure time and improves the cannulation success rate at a lower cost than current alternatives. This thesis gives in-depth background on the development of endoscopic ultrasound (EUS), focusing on the importance of illumination and flexibility for internal tract access and visualization. With EUS-guidance, endoscopists lower access devices to the pancreaticobiliary walls to image and treat ductal blockages, lesions, and stones. With the mechanism established, we delineate the limitations of current non-specialized ERCP techniques and explain how Boston Scientific's EUS access 3-in-1 gamechanger addresses those pullbacks. This thesis also outlines the process development validation and verification steps involved in transforming the design specifications of a 3-in-1 ERCP access gamechanger into a reliably manufactured product that meets performance and regulatory standards. It describes the manufacturing processes and associated parameters for the device's puncture needle coating, device joints adhesion, and access cannula material's shape memory effect and super-elasticity. Finally, we conclude with a summary of process risk analysis, equipment qualifications, and process characterizations activities performed as a Boston Scientific Endoscopy Process Development co-op on the EUS access 3-in-1 ERCP gamechanger device. Primary Reader and Advisor: Dr. Marc Donohue Secondary Reader: Dr. Sakul Ratanaler