Pressure-sensitive Materials Research Articles

Study on Stress and Strain Field of Mode II Quasi-Static Growing Crack in Pressure-Sensitive Dilatant Material

A mechanical model of the pressure-sensitive dilatant material is established in order to investigate the viscous effect in quasi-static growing crack-tip field. The constitutive equations on the pressure-sensitive dilatant material are deducted. Through asymptotic analysis, it is shown that in the stable creep growing stage, the elastic-deformation and the visco-deformation are equally dominant in the near-tip field, as . The asymptotic solutions of separative variable in the crack-tip field of plane stress mode II quasi-static are aslo obtained. According to numerical calculation, the curves of stress, strain and displacement in terms of various parameters are given. The asymptotic solutions of quasi-static growing crack-tip field gained here can conveniently degenerate the incompressible case, when the Poisson ratio , named as HR field. The conclusions can provide the references for further studying the dynamic growing crack-tip field in the pressure-sensitive dilatant material.

The asymptotic field of mode I quasi-static crack growth on the interface between a rigid and a pressure-sensitive material

A mechanical model of the quasi-static interface of a mode I crack between a rigid and a pressure-sensitive viscoelastic material was established to investigate the mechanical characteristic of ship-building engineering bi-materials. In the stable growth stage, stress and strain have the same singularity, ie (σ, e) ∞ r−1/(n−1). The variable-separable asymptotic solutions of stress and strain at the crack tip were obtained by adopting Airy’s stress function and the numerical results of stress and strain in the crack-tip field were obtained by the shooting method. The results showed that the near-tip fields are mainly governed by the power-hardening exponent n and the Poisson ratio ν of the pressure-sensitive material. The fracture criterion of mode I quasi-static crack growth in pressure-sensitive materials, according to the asymptotic analyses of the crack-tip field, can be viewed from the perspective of strain.

Application of Magnetoelastic Thick Films for Wireless, In Vivo Monitoring of Pressure at Abdominal Aortic Aneurysm

According to the National Center for Health Statistics, cardiovascular diseases remain the number one killer in the United States. Among the various types of cardiovascular diseases, the aortic aneurysm is ranked number nine. The abdominal aortic aneurysm (AAA), in particular, is an abnormal, localized dilation of the abdominal aorta wall caused by weakened or diseased aorta walls. One of the treatments for this disease is using an endovascular surgery at which an endovascular graft is delivered to the aneurysm site through the femoral arteries. The deployment of the endovascular graft will exclude blood flow to the aneurysm, thus preventing further expansion of the aneurysm sac. Although this technique is preferred over open surgeries due to its minimal invasiveness, an event known as the endoleak, where the endovascular graft fails to retain the blood and leads to leakage to the aneurysm sac, may occur. Here, we are developing a novel pressure monitoring system to remotely and continuously measure the pressure in the aneurysm sac. The main component of the system is a pressure-sensitive material, made of a magnetoelastic, magnetically soft film attached or coated on the endovascular graft. When under an AC magnetic field (excitation field), the magnetoelastic film generates a secondary magnetic field. Due to its magnetoelastic property, the amplitude of the secondary field varies with applied stresses, allowing remote pressure monitoring. To eliminate noises from the excitation field, the generated secondary field is measured at twice the excitation frequency to obtain the 2nd-order harmonic field, which is used for tracking the pressure variations. A scaled-up prototype of the pressure monitoring system was constructed and examined to demonstrate the feasibility of this technology. A commercial magnetoelastic thick film, Metglas 2826MB from Metglas, Inc., was attached on a polycarbonate substrate and covered by a thin polycarbonate protective layer. The substrate was then embedded in a plastic tube with flowing liquid to represent the condition of an aorta. Liquid pressure in the tube was altered during the experiment by restricting or relaxing the flow channel. In this study, a 10mm×40mm file (Film A) and a 5mm×40mm film (Film B) were fabricated and tested. The amplitude of the 2nd-order harmonic field produced by the films was inversely proportional to the fluid pressure. It was also shown that films with different sizes exhibited different signal sensitivity with the smaller film (Film B) exhibited greater sensitivity. This experiment indicates that feasibility of the pressure monitoring technology.

Construction of a constitutive model in calculations of pressure-dependent material

To make constitutive modeling of materials more approaching reality, a new theory is proposed, in which a corresponding constitutive model can be constructed and characterized experimentally via two steps, one relates to the characterization of yielding behavior of material, and the second relates to the characterization of plastic flow of material deformation. The constitutive model involves two functions, yield function and plastic potential. A relationship between two functions is suggested, therefore, a corresponding plastic potential can be easily created after we have an appropriate yield function. To consider the non-isotropic hardening feature of strength differential in the constitutive model, the concept of equivalent hardening state is introduced, and then, multi-experimental flow stresses can be addressed in the model. When pressure sensitive materials are taken as an example in discussions, the Drucker–Prager yield function is employed to express the yielding behavior of material and a differently experimental characterization of the model is created as the corresponding plastic potential to describe the feature of plastic flow of material. This simple constitutive model can reproduce three sets of experimental results; including two flow-stresses and the volumetric plastic strain. The constitutive model can also well predict stress–strain relations with different pressures loaded on the material. Study shows that the feature of plastic flow is not that sensitive to the pressure loaded on the material when the yielding stress is.

Effects of pressure-sensitive yielding on stress distributions in crankshaft sections under fillet rolling and bending fatigue tests

In this paper, the evolution equation for the active yield surface during the unloading/reloading process based on the Drucker–Prager yield function and a recently developed anisotropic hardening rule is first presented. A user material subroutine based on the anisotropic hardening rule and the constitutive relation was written and implemented into the commercial finite element program ABAQUS. Computations were first conducted for a simple plane strain finite element model under uniaxial monotonic and cyclic loading conditions. The results indicate that the anisotropic hardening rule with the non-associated flow rule describes well the strength-differential effect and the asymmetric closed hysteresis loops as observed in the uniaxial cyclic loading tests of cast irons. Then, a two-dimensional plane strain finite element analysis of a crankshaft section under fillet rolling and subsequent bending was conducted. For the pressure sensitivity corresponding to the cast iron crankshaft of interest, the critical locations for fatigue crack initiation according to the stress distributions for pressure-sensitive materials agree with the experimental observations in bending fatigue tests of crankshaft sections.

Tableting and tablet properties of alginates: Characterisation and potential for Soft Tableting

The aim of the study was to evaluate the suitability of alginates for Soft Tableting. For this purpose the compaction properties of alginates, varying in molecular weight, guluronic acid/mannuronic acid ratio and salt, were investigated and compared to MCC. Based on the mechanical properties, the suitability of the tested excipients for Soft Tableting was predicted. In order to test the prediction the tested materials were used to tablet enteric coated pellets, which served as a pressure sensitive material. The tableting behaviour was analysed by the 3-D modeling technique. The tablet properties were analysed by determining the elastic recovery and the compactibility. Alginates in general deformed elastically. The compression behaviour depended on the chemical composition of the alginates with sodium alginates being more elastic than potassium alginates. Tablets containing alginates with low guluronic acid content exhibited higher elasticity than tablets with alginates having a low mannuronic acid content. The plasticity of potassium alginates was higher than for sodium alginates. However, the plasticity of all tested alginates was lower than the plasticity of MCC. The compactibility of the tested alginates was sufficient. The proposed prediction, which states that tableting excipients with higher elasticity are more suitable for tableting sensitive materials than plastic excipients, was valid for the tested materials. The elastic alginates inflicted less damage on the pellets than the plastic MCC. Thus, all alginates were more appropriate for tableting pressure sensitive materials than MCC.

A generalized anisotropic hardening rule based on the Mroz multi-yield-surface model for pressure insensitive and sensitive materials

In this paper, a generalized anisotropic hardening rule based on the Mroz multi-yield-surface model for pressure insensitive and sensitive materials is derived. The evolution equation for the active yield surface with reference to the memory yield surface is obtained by considering the continuous expansion of the active yield surface during the unloading/reloading process. The incremental constitutive relation based on the associated flow rule is then derived for a general yield function for pressure insensitive and sensitive materials. Detailed incremental constitutive relations for materials based on the Mises yield function, the Hill quadratic anisotropic yield function and the Drucker–Prager yield function are derived as the special cases. The closed-form solutions for one-dimensional stress–plastic strain curves are also derived and plotted for materials under cyclic loading conditions based on the three yield functions. In addition, the closed-form solutions for one-dimensional stress–plastic strain curves for materials based on the isotropic Cazacu–Barlat yield function under cyclic loading conditions are summarized and presented. For materials based on the Mises and the Hill anisotropic yield functions, the stress–plastic strain curves show closed hysteresis loops under uniaxial cyclic loading conditions and the Masing hypothesis is applicable. For materials based on the Drucker–Prager and Cazacu–Barlat yield functions, the stress–plastic strain curves do not close and show the ratcheting effect under uniaxial cyclic loading conditions. The ratcheting effect is due to different strain ranges for a given stress range for the unloading and reloading processes. With these closed-form solutions, the important effects of the yield surface geometry on the cyclic plastic behavior due to the pressure-sensitive yielding or the unsymmetric behavior in tension and compression can be shown unambiguously. The closed form solutions for the Drucker–Prager and Cazacu–Barlat yield functions with the associated flow rule also suggest that a more general anisotropic hardening theory needs to be developed to address the ratcheting effects for a given stress range.

Bemis Co Inc

AbstractPaper Products (MIC: SIC: 2671 NAIC: 322221)Bemis Company is a manufacturer of flexible packaging products and pressure sensitive materials, selling to customers mainly in the food industry in the U.S., Canada, South America, Europe, Asia Pacific and Mexico. Through its Flexible Packaging segment, Co. produces a range of food, consumer goods, and industrial packaging. Multilayer flexible polymer film structures and laminates are sold for food, medical and personal care products as well as non‐food applications utilizing vacuum or modified atmosphere packaging. Through its Pressure Sensitive Materials segment, Co. produces pressure sensitive adhesive coated paper and film substrates sold into the label, graphic and technical markets.

A methodology to assess the rate and pressure sensitivity of polymers over a wide range of strain rates

This paper details a methodology to test the mechanical response of soft, pressure sensitive materials, over a wide range of strain rates. A hybrid experimental–numerical procedure is used to assess the constitutive parameters. The experimental phase involves axial compression of a cylindrical specimen which is confined by a tightly-fit sleeve that is allowed to yield plastically, thus applying a constant confining pressure. The usually neglected frictional effects between the specimen and the sleeve are fully accounted for and characterized in detail. With commercial polycarbonate as a typical example, it is shown that pressure sensitivity and rate sensitivity are not coupled, thus reducing the number of tests needed to characterize a material. The results of numerical simulations indicate that the pressure sensitivity index (angle β in the Drucker-Prager material model) has little influence on the hydrostatic and confining pressures, whereas the equivalent stress sustained by the specimen increases with β, which for commercial polycarbonate is found to be β=15°.

Pressure-sensitive adhesive materials for operational maintenance of equipment

The properties of pressure-sensitive adhesive materials, namely, an adhesive-based film protective coating, a pressure-sensitive aluminum foil, and an aluminum foil-based pressure-sensitive material with a permanent tacky layer are described. The materials are shown to be applicable for occasional maintenance of damages (scratches, chips, or peels of lacquer coatings) on external surfaces of aircraft frames.

Bemis Co Inc

AbstractPaper Products (MIC: SIC: 2671 NAIC: 322221)Bemis Company is a manufacturer of flexible packaging products and pressure sensitive materials, selling to customers mainly in the food industry in the U.S., Canada, South America, Europe, Asia Pacific and Mexico. Through its Flexible Packaging segment, Co. produces a range of food, consumer goods, and industrial packaging. Multilayer flexible polymer film structures and laminates are sold for food, medical and personal care products as well as non‐food applications utilizing vacuum or modified atmosphere packaging. Through its Pressure Sensitive Materials segment, Co. produces pressure sensitive adhesive coated paper and film substrates sold into the label, graphic and technical markets.

Simulations of stress distributions in crankshaft sections under fillet rolling and bending fatigue tests

The residual stresses due to fillet rolling and the bending stresses near the fillets of crankshaft sections under bending fatigue tests are important driving forces to determine the bending fatigue limits of crankshafts. In this paper, the residual stresses and the bending stresses near the fillet of a crankshaft section under fillet rolling and subsequent bending fatigue tests are investigated by a two-dimensional plane strain finite element analysis based on the anisotropic hardening rule of Choi and Pan [Choi KS, Pan J. A generalized anisotropic hardening rule based on the Mroz multi-yield-surface model for pressure insensitive and sensitive materials (in preparation)]. The evolution equation for the active yield surface during the unloading/reloading process is first presented based on the anisotropic hardening rule of Choi and Pan (in preparation) and the Mises yield function. The tangent modulus procedure of Peirce et al. [Peirce D, Shih CF, Needleman A. A tangent modulus method for rate dependent solids. Comput Struct 1984;18:875–87] for rate-sensitive materials is adopted to derive the constitutive relation. A user material subroutine based on the anisotropic hardening rule and the constitutive relation was written and implemented into ABAQUS. Computations were first conducted for a simple plane strain finite element model under uniaxial monotonic and cyclic loading conditions based on the anisotropic hardening rule, the isotropic and nonlinear kinematic hardening rules of ABAQUS. The results indicate that the plastic response of the material follows the intended input stress–strain data for the anisotropic hardening rule whereas the plastic response depends upon the input strain ranges of the stress–strain data for the nonlinear kinematic hardening rule. Then, a two-dimensional plane-strain finite element analysis of a crankshaft section under fillet rolling and subsequent bending was conducted based on the anisotropic hardening rule of Choi and Pan (in preparation) and the nonlinear kinematic hardening rule of ABAQUS. In general, the trends of the stress distributions based on the two hardening rules are quite similar after the release of roller and under bending. However, the compressive hoop stress based on the anisotropic hardening rule is larger than that based on the nonlinear kinematic hardening rule within the depth of 2 mm from the fillet surface under bending with consideration of the residual stresses of fillet rolling. The critical locations for fatigue crack initiation according to the stress distributions based on the anisotropic hardening rule appear to agree with the experimental observations in bending fatigue tests of crankshaft sections.

Bemis Co Inc

AbstractPaper Products (MIC: 11.11 SIC: 2671 NAIC: 322221)Bemis is a manufacturer of flexible packaging products and pressure sensitive materials, selling to customers primarily in the food industry throughout the U.S., Canada, South America, Europe, Asia Pacific and Mexico. Through its Flexible Packaging segment, Co. manufactures a range of consumer and industrial packaging such as multilayer flexible polymer film structures and laminates that are sold for food, medical and personal care products as well as non‐food applications utilizing vacuum or modified atmosphere packaging. Co.'s Pressure Sensitive Materials segment manufactures pressure sensitive materials that are sold into label markets, graphic markets and technical markets.

Bemis Co Inc

AbstractPaper Products (MIC: 11.11 SIC: 2671 NAIC: 322221)Bemis is a manufacturer of flexible packaging products and pressure sensitive materials, selling to customers primarily in the food industry throughout the U.S., Canada, South America, Europe, Asia Pacific and Mexico. Through its Flexible Packaging segment, Co. manufactures a range of consumer and industrial packaging such as multilayer flexible polymer film structures and laminates that are sold for food, medical and personal care products as well as non‐food applications utilizing vacuum or modified atmosphere packaging. Co.'s Pressure Sensitive Materials segment manufactures pressure sensitive materials that are sold into label markets, graphic markets and technical markets.

Arbitrary Lagrangian–Eulerian method in plasticity of pressure-sensitive material: application to powder forming processes

In this paper, an application of Arbitrary Lagrangian–Eulerian (ALE) method is presented in plasticity behavior of pressure-sensitive material, with special reference to large deformation analysis of powder compaction process. In ALE technique, the reference configuration is used for describing the motion, instead of material configuration in Lagrangian, and spatial configuration in Eulerian formulation. The convective term is used to reflect the relative motion between the mesh and the material. Each time-step is divided into the Lagrangian phase and Eulerian phase. The convection term is neglected in the material phase, which is identical to a time-step in a standard Lagrangian analysis. The stresses and plastic internal variables are converted to account the relative mesh-material motion in the convection phase. The ALE formulation is then performed within the framework of a three-invariant cap plasticity model in order to predict the non-uniform density distribution during the large deformation of powder die pressing. The plasticity model is based on a hardening rule with the isotropic and kinematic material functions. The constitutive elasto-plastic matrix and its components are derived by using the definition of yield surface, material functions and non-linear elastic behavior, as function of hardening parameters. Finally, the numerical examples are performed to illustrate the applicability of the computational algorithm in modeling of powder forming process and the results are compared with those obtained from Lagrangian simulation in order to demonstrate the accuracy of proposed model.

Gurson Model and Conic Programming for Pressure-Sensitive Materials

In this talk we analyze the yield criterion of a porous material containing cylindrical and spherical cavities on the basis of the Gurson mechanical model where the matrix is pressuresensitive. Both limit analysis (LA) methods are used to determine as closely as possible the corresponding macroscopic criterion, by using conic programming formulations. For a Drucker-Prager matrix the case of cylindrical cavities is investigated in generalized plane strain, and the results compared with those of previous works for von Mises matrices. Then we study the case of a Coulomb matrix for spherical cavities under axisymmetrical conditions. Due to the constraining character of the axisymmetry, specific analytical solutions are superimposed on the numerical fields. Among other results, a comparison with an ad hoc translated “modified Cam-Clay criterion” points out that it might be considered as a satisfactory approximation, except that it does not account for the corner of our criterion on the isotropic compressive axis, unlike the original Cam-Clay criterion.

Bemis Co Inc

AbstractPaper Products (MIC: 11.11 SIC: 2671 NAIC: 322221)Bemis is a manufacturer of flexible packaging products and pressure sensitive materials, selling to customers primarily in the food industry throughout the U.S., Canada, South America, Europe, Asia Pacific and Mexico. Through its Flexible Packaging segment, Co. manufactures a range of consumer and industrial packaging such as multilayer flexible polymer film structures and laminates that are sold for food, medical and personal care products as well as non‐food applications utilizing vacuum or modified atmosphere packaging. Co.'s Pressure Sensitive Materials segment manufactures pressure sensitive materials that are sold into label markets, graphic markets and technical markets.

A Note on the Direct Determination of the Confining Pressure of Cylindrical Specimens

This note presents a simple approach to the direct determination of the confining pressure, q, for a cylindrical specimen encased in a metallic sleeve. The stress analysis of the problem shows that, for a pressure-insensitive material (e.g. metal), q is the quantity by which the stress level of the confined specimen is elevated with respect to the unconfined. As such, q is directly determined by comparing the results of two tests, one with and the second without confinement. For a pressure-sensitive material, q must be determined independently from a plastic stress analysis of the confining sleeve. Then, the same approach can be applied to determine the pressure sensitivity of the material. The present results greatly simplify testing of confined cylindrical specimens for both pressure-insensitive and sensitive materials.

Bemis Co Inc

AbstractPaper Products (MIC: 11.11 SIC: 2671 NAIC: 322221)Bemis is a manufacturer of flexible packaging products and pressure sensitive materials selling to customers primarily in the food industry throughout the U.S., Canada, South America, Europe, Asia Pacific and Mexico. Through its Flexible Packaging segment, Co. manufactures a range of consumer and industrial packaging such as multilayer flexible polymer film structures and laminates that are sold for food, medical and personal care products as well as non‐food applications utilizing vacuum or modified atmosphere packaging. Co.'s Pressure Sensitive Materials segment manufactures pressure sensitive materials that are sold into label markets, graphic markets and technical markets.

Bemis Co Inc

AbstractPaper Products (MIC: 11.11 SIC: 2671 NAIC: 322221)Bemis is a manufacturer of flexible packaging products and pressure sensitive materials selling to customers primarily in the food industry throughout the U.S., Canada, South America, Europe, Asia Pacific and Mexico. Through its Flexible Packaging segment, Co. manufactures a range of consumer and industrial packaging such as multilayer flexible polymer film structures and laminates that are sold for food, medical and personal care products as well as non‐food applications utilizing vacuum or modified atmosphere packaging. Co.'s Pressure Sensitive Materials segment manufactures pressure sensitive materials that are sold into label markets, graphic markets and technical markets.