Dynamic Bulge Research Articles

Determination of the Plastic Stress–Strain Relationship of a Rupture Disc Material with Quasi-Static and Dynamic Pneumatic Bulge Processes

Rupture discs, manufactured using a hydraulic or pneumatic bulge process, are widely used to protect vessels from over-pressuring. The stress–strain relationship of the material in the bulge process plays a major role in understanding the performance of rupture discs. Moreover, both the theoretical analyses and numerical simulations of rupture discs demand a reliable stress–strain relationship of the material in a real bulge process. In this paper, an approach for determining the plastic stress–strain relationship of a rupture disc material in the bulge process is proposed based on plastic membrane theory and force equilibrium equations. Pressures of compressed air and methane/air mixture explosions were used for the bulge pressure to accomplish the quasi-static and dynamic bulge processes of tested discs. Experimental apparatus for the quasi-static bulge test and the dynamic bulge test were built. The stress–strain relations of 316L material during bulge tests were obtained, compared, and discussed. The results indicated that the bulge height at the top of the domed disc increased linearly with an increase in bulge pressure in the quasi-static and dynamic bulge processes, and the effective strain increased exponentially. The rate of pressure rise during the bulge process has a significant effect on the deformation behavior of disc material and hence the stress–strain relationship. At the same bulge pressure, a disc tested with a larger pressure rise rate had smaller bulge height and effective strain. At the same effective stress at the top of the domed disc, discs subjected to a higher pressure rise rate had smaller effective strain, and hence they are more difficult to rupture. Hollomon’s equation is used to represent the relationship between the effective stress and strain during bulge process. For pressure rise rates in the following range of 0 (equivalent to quasi-static condition), 2–10 MPa/s, 10–50 MPa/s, and 50–100 MPa/s, the relation of stress and strain is σe = 1259.4·εe0.4487, σe = 1192.4·εe0.3261, σe = 1381.2·εe0.2910, and σe = 1368.4·εe0.1701, respectively.

On the Anisotropic Mechanical Response of Ti6Al4V Sheet at High Strain Rates

In traditional sheet metal forming processes, a thin sheet metal is deformed at relatively low speeds. However, more and more the speed of production processes is increased, very often to take advantage of the beneficial implications that high strain rates can have on the formability of certain metals. In this work, the effect of strain rate on the anisotropic behavior of Ti6Al4V is investigated performing tensile tests in different orientations, namely 0o, 45o and 90o, with respect to the rolling direction (RD), and in-plane shear experiments along RD. Three nominal strain rates, i.e., , 0.5 and 1000, are considered. A novel high-speed bulge (HSB) test developed at Ghent University, designed to deform sheet metals in nearly equibiaxial loading conditions at high strain rates, is used for the dynamic bulge test. The experimental results, presented in this paper, clearly show the need of including the effect of strain rate, and eventually temperature, into the formulation of the yield function in order to correctly model and predict deformation processes performed at high speed.

Dynamic bulge nucleotides in the KSHV PAN ENE triple helix provide a unique binding platform for small molecule ligands.

Cellular and virus-coded long non-coding (lnc) RNAs support multiple roles related to biological and pathological processes. Several lncRNAs sequester their 3' termini to evade cellular degradation machinery, thereby supporting disease progression. An intramolecular triplex involving the lncRNA 3' terminus, the element for nuclear expression (ENE), stabilizes RNA transcripts and promotes persistent function. Therefore, such ENE triplexes, as presented here in Kaposi's sarcoma-associated herpesvirus (KSHV) polyadenylated nuclear (PAN) lncRNA, represent targets for therapeutic development. Towards identifying novel ligands targeting the PAN ENE triplex, we screened a library of immobilized small molecules and identified several triplex-binding chemotypes, the tightest of which exhibits micromolar binding affinity. Combined biophysical, biochemical, and computational strategies localized ligand binding to a platform created near a dinucleotide bulge at the base of the triplex. Crystal structures of apo (3.3 Å) and ligand-soaked (2.5 Å) ENE triplexes, which include a stabilizing basal duplex, indicate significant local structural rearrangements within this dinucleotide bulge. MD simulations and a modified nucleoside analog interference technique corroborate the role of the bulge and the base of the triplex in ligand binding. Together with recently discovered small molecules that reduce nuclear MALAT1 lncRNA levels by engaging its ENE triplex, our data supports the potential of targeting RNA triplexes with small molecules.

Deformation and fracture behaviors of copper sheet in laser dynamic flexible forming

Laser dynamic flexible forming (LDFF) is a novel high velocity forming (HVF) technology, in which the high-energy laser shock waves act on the workpiece via a flexible medium. Dynamic bulge tests of copper sheet are performed to investigate the deformation and fracture behaviors in LDFF in this paper. The laser ablation states on K9 glass surfaces under different laser energies were characterized. The samples after LDFF were characterized by optical microscopy and scanning electron microscopy. For laser energy ranging from 1020 mJ to1380 mJ, as laser energy increases, the average surface roughness (Ra) in bulge region rapidly increases due to surface free forming. However, the Ra in laser shock compression region slowly decreases due to shock flattening. Strain localization occurs around the bulge edge, and the composition of oxygen element in this region is increased with laser energy. When laser energy is equal to or greater than 1690 mJ, localized deformation evolved into the dynamic failure. Apart from the elongated micro-voids, three interesting phenomena were observed: the melting marks, the serrated fracture boundaries and filaments. As the laser energy increases, the fracture mode varies from a tensile fracture mode to a shear fracture mode, then to a filament fracture mode. The filament fracture mode indicates that superplastic flow of material may exist until fracture, and oxidation behaviors make a great contribution to the superplastic flow.

Crack formation on metal foils during high dynamic and quasi-static bulge test

Resource efficiency combined with high-strength materials is the key to enable intelligent lightweight design. Forming processes, such as high speed forming processes, have a high degree of material utilization compared to other manufacturing processes. In the micro range, processes based on laser induced shockwaves are promising for high speed forming operations. High speed forming offers the possibility to achieve high strain rates and accordingly the forming limit of thin metallic foils can be increased compared to conventional forming operation. However, the effect of the increased forming limit is not completely understood. Therefore, in this work the position of the crack initiation is investigated for quasi-static and dynamic bulge tests. The investigated material is Al99.5 and CU-ETP1 in the thicknesses of 20 μm and 50 μm. It is found, that the crack formation for quasi-static forming is showing a stochastic distribution over the formed area, while the crack initiation for the dynamic forming process is in the centre. This behaviour is explained by an increase in material temperature during the laser shock forming process, which is decreasing the flow stress in the centre of the forming area, thus the crack initiation is located in this area.

Breakout of squeezed stocks: dispersal of roof fragments, source of extrusive salt and interaction with regional thrust faults

AbstractWe used seven scaled physical models to explore the near‐surface structural evolution of shallowly buried, actively rising salt stocks. The models consisted of dry sand, ceramic microspheres and silicone. Previously dormant stocks rose because of lateral squeezing or pumping of salt from below. The pressure of rising salt created a dynamic bulge in the crest of the diapir, which arched the overlying roof sediments. Eventually this dynamic bulge collapsed and its overlying roof broke into rafts along subradial grabens. The rafts were dispersed outwards by shear traction of spreading salt, surmounting an upturned collar of country rock and eventually grounding at the front of the extrusive flow. Flow of salt around these stranded fragments created a lobate extrusion front, common in submarine salt sheets in the Gulf of Mexico and subaerial salt glaciers in Iran. Stock geometry, regional dip and roof density affected extrusion rates and spreading directions. Stocks leaning seaward extruded salt faster and farther than did upright stocks. Dense roofs foundered and plugged the vent, limiting surface extrusion. In tilted models, broad salt sheets spread asymmetrically downslope. Stock contents were inverted within the extruded salt sheet: successively deeper parts of the stock's core rose to the surface and overran salt extruded from the shallower parts of the diapir. As shortening continued, salt from the source layer reached the surface after being driven out by thrusting. A central thrust block, or primary indenter, moved ahead of surrounding thrust blocks, impinging against and squeezing the stock into an elliptical planform. After high shortening, secondary indenters converged obliquely into the salt stock, expelling salt from the periphery of the diapir. The models shed light on (1) the origin and fate of large rafts or carapace blocks atop allochthonous salt, (2) cuspate margins of salt sheets and (3) interaction of thrusting, diapir pinch‐off and emplacement of allochthonous salt sheets.

Use of a shock tube to determine the bi-axial yield of an aluminum alloy under high rates

This paper presents a method for extracting the bi-axial rate dependent mechanical properties of thin homogenous materials, using a shock tube, demonstrated here using an aluminum alloy sheet. Rate dependence determination techniques such as Split Hopkinson Pressure Bar (SHPB) have long been used for determining uniaxial properties. Recent advances have led to modification of the SHPB to include a bulge cell to develop a so called “dynamic bulge test”. Due to the relative fixed nature of the SHPB, it is difficult to obtain lower strain rate response without significantly modifying the test fixture. Using shock wave loading, and a flat, circular thin plate specimen, a state of biaxial tensile stress is created at the center of the crown during intermediate to high rates of loading. An inverse modeling technique in conjunction with a finite element (FE) simulation technique is used to determine the rate dependent constitutive properties of the plate material. This work demonstrates the applicability of the shock loading method for extracting rate dependent properties of materials available in thin sheet form by using commercial grade aluminum. A finite element model of the shock response is used to determine the strain rate dependent mechanical properties using an optimization algorithm and an inverse modeling method. The results were found to be in agreement with previous literature and good correlation between the model and experimental results are presented here.

The relationship between degree of facet tropism and amount of dynamic disc bulge in lumbar spine of patients symptomatic for low back pain

Facet tropism has been investigated as a predisposing factor for degenerative changes in the lumbar spine; however, no prior study has evaluated the relationship between disc bulge and facet tropism. In this study, we used kinetic magnetic resonance imaging (kMRI) to investigate the association between degree of facet tropism and amount of disc bulge in the lumbar spine in relation to age. kMRIs in the flexion, neutral, and extension positions were performed on 410 consecutive patients with low back pain. T2-weighted midsagittal and axial mid-disc cuts were analyzed to measure disc bulge and facet angle. Facet asymmetry was calculated and classified as: no facet tropism, <6°; mild facet tropism, 6–11°; or severe facet tropism, ≥11°. Maximal static bulge (MSB), maximal dynamic bulge (MDB), and age in the facet tropism groups were compared by age subpopulations and MDB categories, defined by the positions between which the largest change in disc bulge occurs. We found the severe facet tropism group to be associated with a nearly significant increase in MSB and MDB over the no facet tropism group in the older subpopulation at the L4–L5 level only, and a larger MDB in the L4–L5 MDB category [E–N], where the greatest change in disc bulge occurs between neutral and extension positions (p = 0.013). Our findings suggest that severe facet tropism is associated with increased disc bulge at L4–L5 in only a subset of older age patients, but may in large part be due to biomechanical factors that define the [E–N] category.

Plastic bulging of sheet metals at high strain rates

The biaxial bulge test is a material test for sheet metals to evaluate formability and determine the flow stress diagram. Due to the biaxial state of stress induced in this test, the maximum achievable strain before fracture is much larger than in the uniaxial tensile test. A new dynamic bulge testing technique is simulated and analyzed in this study which can be performed on a conventional split Hopkinson pressure bar (SHPB) system to evaluate the strain-rate dependent strength of material at high impact velocities. Polyurethane rubber as pressure carrying medium is used to bulge the OFHC copper sheet. The use of hyperelastic rubber instead of fluid as a pressure medium makes the bulge test simple and easy to perform. The input bar of SHPB is used to apply and measure the bulging pressure. The finite element simulation using ABAQUS/explicit and analytical analysis are compared and show good correlation with each other. The results clearly show that as the strain-rate increases, the strength of the OFHC copper increases. From the study, a robust method to determine the material behavior under dynamically biaxial deformation conditions has been developed.

Structure and Function of the Pre-mRNA Splicing Machine

Most eukaryotic pre-mRNAs contain non-coding sequences (introns) that must be removed in order to accurately place the coding sequences (exons) in the correct reading frame. This critical regulatory pre-mRNA splicing event is fundamental in development and cancer. It occurs within a mega-Dalton multicomponent machine composed of RNA and proteins, which undergoes dynamic changes in RNA-RNA, RNA-protein, and protein-protein interactions during the splicing reaction. Recent years have seen progress in functional and structural analyses of the splicing machine and its subcomponents, and this review is focused on structural aspects of the pre-mRNA splicing machine and their mechanistic implications on the splicing of multi-intronic pre-mRNAs. It brings together, in a comparative manner, structural information on spliceosomes and their intermediates in the stepwise assembly process in vitro, and on the preformed supraspliceosomes, which are isolated from living cell nuclei, with a view of portraying a consistent picture.

Dynamic rupture of polymer–metal bilayer plates

Recent theoretical assessments of metal/polymer bilayers indicate a potentially significant delay in the onset of ductile failure modes, especially under dynamic loading, due to strain hardening of the polymer. The response of copper/polyurethane bilayers under dynamic and quasi-static loadings is investigated via static tensile, static bulge forming and dynamic bulge forming tests. Two polyurethanes PU1 and PU2 were chosen with a significant contrast in stiffness and ductility: PU1 has a glass transition temperature T g close to −56 °C and at room temperature it has a low modulus, low strength and a high tensile failure strain. In contrast, PU2 has a T g of 49 °C and at room temperature it has a high modulus and strength but a much smaller tensile failure strain. In most of the tests, the polymer coatings were approximately twice the thickness of the metal layer. Under static loadings (tensile and bulge forming) the PU2 bilayer outperformed the uncoated metal plate of equal mass while the PU1 bilayer had a performance inferior to the equivalent uncoated plate. We attribute this to the fact that the PU2 retards the necking of the copper layer and thus increases its energy absorption capacity while the PU1 coating provides no such synergistic effect. The dynamic bulge forming tests indicate that on an equal mass basis, the dynamic performance of the PU2 bilayers with a weakly bonded polymer coating were comparable to the uncoated plates but intriguingly, when the PU2 was strongly adhered to the copper plates the performance of these bilayers was inferior to that of the uncoated plates. Thus, the coatings do not provide dynamic performance benefits on an equal mass basis. However, it is shown that increasing the mass of a plate by adding a polyurethane layer can improve the performance for a given total blast impulse. Given the ease of applying polyurethane coatings they may provide a practical solution to enhancing the blast resistance of existing metallic structures.

A dynamic bulge in the U6 RNA internal stem–loop functions in spliceosome assembly and activation

The highly conserved internal stem-loop (ISL) of U6 spliceosomal RNA is unwound for U4/U6 complex formation during spliceosome assembly and reformed upon U4 release during spliceosome activation. The U6 ISL is structurally similar to Domain 5 of group II self-splicing introns, and contains a dynamic bulge that coordinates a Mg++ ion essential for the first catalytic step of splicing. We have analyzed the causes of growth defects resulting from mutations in the Saccharomyces cerevisiae U6 ISL-bulged nucleotide U80 and the adjacent C67-A79 base pair. Intragenic suppressors and enhancers of the cold-sensitive A79G mutation, which replaces the C-A pair with a C-G pair, suggest that it stabilizes the ISL, inhibits U4/U6 assembly, and may also disrupt spliceosome activation. The lethality of mutations C67A and C67G results from disruption of base-pairing potential between U4 and U6, as these mutations are fully suppressed by compensatory mutations in U4 RNA. Strikingly, suppressor analysis shows that the lethality of the U80G mutation is due not only to formation of a stable base pair with C67, as previously proposed, but also another defect. A U6-U80G strain in which mispairing with position 67 is prevented grows poorly and assembles aberrant spliceosomes that retain U1 snRNP and fail to fully unwind the U4/U6 complex at elevated temperatures. Our data suggest that the U6 ISL bulge is important for coupling U1 snRNP release with U4/U6 unwinding during spliceosome activation.

Quantification of Constitutive Behavior of Sheet Metals Subjected to Dynamic Bulge Loading

Abstract A newly developed method has been employed to quantify the mechanical behavior of sheet metals (both isotropic and orthotropic) subjected to dynamic bulge loading at strain rates of up to 400 s−1. Using newly developed dynamic bulge testing equipment with stereoscopic imaging, the exact shape of the bulging dome has been obtained and represented using high order polynomials before further constitutive analysis. The bulge profile functions discerned have been used to calculate the actual radius of curvature at the pole, thus replacing the spherical shape generally assumed in traditional bulge test analysis. Furthermore, the calculation of the thickness of the bulge has been improved by employing “dome volume” approaches. Effective strain and stress at the dome’s pole have been calculated considering both isotropic and orthotropic materials. The effect of gage length on the obtained values of strain and stress has been assessed.

Biaxial Testing of Sheet Materials at High Strain Rates Using Viscoelastic Bars

A dynamic bulge testing technique is developed to perform biaxial tests on metals at high strain rates. The main component of the dynamic testing device is a movable bulge cell which is directly mounted on the measuring end of the input bar of a conventional split Hopkinson pressure bar system. The input bar is used to apply and measure the bulging pressure. The experimental system is analyzed in detail and the measurement accuracy is discussed. It is found that bars made of low impedance materials must be used to achieve a satisfactory pressure measurement accuracy. A series of dynamic experiments is performed on aluminum 6111-T4 sheets using viscoelastic nylon bars to demonstrate the capabilities of the proposed experimental technique. The parameters of the rate-dependent Hollomon–Cowper–Symonds J2 plasticity model of the aluminum are determined using an inverse analysis method in conjunction with finite element simulations.

Index of Suspicion

Index of Suspicion

Relationships Between Microstructure and Reliability in Pzt Mems

ABSTRACTPiezoelectric oxide films, such as lead zirconate titanate (PZT), are now being integrated into MEMS applications. Many PZT derived systems are deposited using a sol-gel process, which can be used in a microelectronics processing route using spin coating as the deposition method. An application of interest for PZT films is in power generation, where a flexing membrane is used to transform mechanical to electrical energy. The current study was undertaken to identify the relationships between the processing, microstructure, and mechanical reliability of these films. Films were deposited onto both monolithic and bulk micromachined platinized silicon wafers using standard sol-gel chemistries, with roughness and grain size tracked using electron and scanning probe microscopy. Mechanical properties were evaluated in a dynamic bulge testing apparatus. Grain size variations in the Pt film between 35 and 125 nm are shown to have little effect on grain size of the subsequent PZT film and the adhesion of the PZT to the Pt film. Only the Pt film with 125 nm grains was shown to undergo any significant interfacial fracture. Fatigue tests suggest film lifetime is primarily limited by the number of pre- existing flaws in the film from processing. Reducing the microcrack density has been shown to produce films and devices that fail at strains of 1.4% and have mechanical fatigue lifetimes in excess of 100 million cycles at strains simulating the operating conditions.

Defects and Failure Modes in PZT Films for a MEMS Microengine

ABSTRACTPiezoelectric films for a MEMS microengine have been deposited using solution deposition routines onto platinized silicon wafers. These films are used as membranes above a bulk micromachined cavity. A dynamic bulge tester and interferometer were used to characterize the deformation of the films when pressurized. The mechanical strain at failure, as well as the fatigue behavior, have been characterized. Membranes between 300 and 500 nm thick have been shown to sustain mechanical fatigue damage over approximately 10 million cycles at strains of 30% of the monotonic failure strain. Defects in the films due to growth and thermal stresses during processing, and their role in membrane failure, are identified. Crack growth is demonstrated in these films by compliance measurements during fatigue testing, and interfacial failure is identified between the PZT and Pt layers.