Effect Of Pressure Cycling Research Articles

Effect of pressure cycles and thermal conditions on the reliability of a high-pressure diecast Al alloy heating radiator

The fatigue reliability of a diecast AlSi11Cu2(Fe) alloy radiator has been investigated at different pressure amplitudes and thermal exposure. Based on failure mode analysis, two failure mechanisms are observed during fatigue testing, i.e. leakage at the interface between the diecast element and the plug, and fatigue fracture of a radiator element. Fatigue life tests have been carried out at two different pressure amplitudes, 3 and 4 MPa, and two holding temperatures, 40 and 60 °C, respectively. The results reveal how the main cause of failure is related to the fatigue failure of a radiator element in the whole heating system. This is due to casting defects such as gas porosity and oxides which are formed during the filling phase of the die cavity in high-pressure die casting. Furthermore, casting defects increase the leakage failure and reduce the fatigue life of the radiator. An increase of the holding temperature increases the frequency of leakage failure of radiators.

High Pressure-Assisted Infusion of Calcium into Baby Carrots Part I: Influence of Process Variables on Calcium Infusion and Hardness of the Baby Carrots

This research was aimed at exploring and evaluating high pressure processing (HPP) as a technique for calcium infusion into baby carrots. HPP was employed in infusing calcium in pectin methylesterase (PME) pre-treated baby carrots using infusate solution of calcium lactate gluconate (CLG). Experiments were performed following a Box-Behnken design to evaluate the effects of pressure, holding time, and CLG concentration on the extent of calcium infusion (amount infused per serving size (85 g) of baby carrots) and the hardness of baby carrots using single pressure cycle. In addition, the effect of pressure cycling on the extent of calcium infusion was also studied by varying the number of high pressure cycles at 1, 3, and 5 at a fixed pressure (550 MPa) for a total holding time of 15 min and using 9% (w/v) CLG solution. HPP enhanced the infusion of calcium from 19.5 mg/serving in raw baby carrots to 134 mg/serving at 350 MPa–10 min–9% CLG, which was more than 3 times the amount of calcium infused in osmotically and vacuum infused controls. Pressure level, time, and CLG concentration had significant effects on calcium infusion. Increasing the number of pressure cycles increased the amount of calcium infused. The calcium infused baby carrots had higher hardness than raw unprocessed carrots.

Cyclic pressure on compression-moulded bioresorbable phosphate glass fibre reinforced composites

The use of thermoplastic composites based on poly(lactic) acid and phosphate glass fibres over metallic alloys for clinical restorative treatment is highly beneficial due to their biocompatibility and biodegradability. However, difficulties in achieving a thorough melt impregnation at high fibre contents while limiting polymer degradation is one of the main issues encountered during their manufacture. This paper reports for the first time on the effects of pressure cycling on the mechanical properties of compression moulded polylactic acid-phosphate glass fibre composites. The strength of the composites consolidated under pressure cycling were at least 30% higher than those in which conventional static pressure was used. The marked disparity was attributed to the influence of pressure cycling on the fibre preform permeability, the melt viscosity and the capillary pressure, leading to improved fibre wet-out with respect to static pressure. Implementation of a cyclic pressure appeared to promote the occurrence of transcrystallinity in the polymer matrix as suggested by DSC traces. The fibre content influenced PLA thermal degradation since the matrix molecular weight decreased as the fibre content increased on account of the moisture adsorbed by the glass surface. However, this extent of degradation did not impair the matrix mechanical performance in the composites.

Inactivation of Bacillus subtilis and Geobacillus stearothermophilus inoculated over metal surfaces using supercritical CO2 process and nisin

The use of supercritical CO2 (SC-CO2) as sterilizing agent of liquids and solid surfaces is arising as one of the most promising alternative sterilization techniques. This technology shows potential to substitute current chemical and thermal processes that, despite efficient, can damage the material. In this study, the effect of supercritical CO2 treatment (with and without ethanol as co-solvent) on the sterilization of Bacillus subtilis and Geobacillus stearothermophilus spores inoculated over metal surfaces were evaluated under pressure of 30MPa and different temperatures (30 and 60°C) and treatment times (60, 120 and 180min). The effects of pressure cycles (ΔP=30MPa) and the addition of a natural antimicrobial agent (nisin) were also tested. Considering the tested conditions, SC-CO2 treatment alone was not able to efficiently reduce spore population of microorganisms. However, an interesting synergic sterilizing effect (more than 7 log cycles) was observed when SC-CO2 treatment was used in combination with low concentrations of nisin.

Effect of pressure cycling on iron: Signatures of an electronic instability and unconventional superconductivity

High pressure electrical resistivity and x-ray diffraction experiments have been performed on Fe single crystals. The crystallographic investigation provides direct evidence that in the martensitic $bcc \rightarrow hcp$ transition at 14 GPa the $\lbrace 110\rbrace_{bcc}$ become the $\lbrace 002\rbrace_{hcp}$ directions. During a pressure cycle, resistivity shows a broad hysteresis of 6.5 GPa, whereas superconductivity, observed between 13 and 31 GPa, remains unaffected. Upon increasing pressure an electronic instability, probably a quantum critical point, is observed at around 19 GPa and, close to this pressure, the superconducting $T_{c}$ and the isothermal resistivity ($0<T<300\,$K) attain maximum values. In the superconducting pressure domain, the exponent $n = 5/3$ of the temperature power law of resistivity and its prefactor, which mimics $T_{c}$, indicate that ferromagnetic fluctuations may provide the glue for the Cooper pairs, yielding unconventional superconductivity.

The effect of pressure cycling on proteolytic cleavage efficiency, reaction time and protein sequence coverage

Over the years many methodologies have been advanced to aid in the enhancement of proteolysis cleavage efficiency, reaction time, and protein sequence coverage for LC‐MS/MS based analysis. The series of experiments presented here examine the effect pressure cycling on each of these factors. Several individual proteins and a simple protein mixture were digested with different proteases under high pressure using a Barocycler NEP2320 pressure cycler and compared to overnight at 1 atm and 37 °C proteolysis conditions. The resulting peptides were identified and quantified using an LC‐MS/MS workflow with a LTQ XL with ETD. The results indicate that digestions using pressure cycling produce more distinct peptides and equivalent or higher protein sequence coverage when compared to standard overnight digestions.

Observations on densification of Al-Al2O3 composite powder compacts by pressure cycling

The effectiveness of pressure cycling on the consolidation of powder composites is investigated. Mixed Al and various amounts of Al2O3 powders were consolidated under static and cyclic pressure at room temperature in uniaxial consolidation experiments. The results showed that each pressure cycle increases green density and the cyclic effect is stronger when there is a relatively large volume fraction of Al2O3 powder. The compacts produced by pressure cycling have much higher strength than those produced with a single pressure excursion and the process ability of compacts should also improve via pressure cycling. Microscopic observations showed that greater uniformity is obtained in compacts by cyclic consolidation. The origin of the beneficial effect of pressure cycling is related to the deviatoric stresses generated by volumetric mismatch due to the different compressibilities of the phases.

The densification of powder mixtures containing soft and hard components under static and cyclic pressure

The effect of pressure cycling on the densification and ejection of Pb–Al 2O 3 powder mixtures is investigated and compared to static loading. The volume fraction of Al 2O 3 is varied between 0 and 80%. The density of all mixtures increases with time under constant pressure even at room temperature. This mechanical behavior is the result of the creep of lead. This effect diminishes with increasing volume fraction of Al 2O 3. Pressure cycling does not have any influence on the final density of lead samples in the absence of Al 2O 3. The influence of cycling becomes, however, noticeable in the presence of Al 2O 3 in the mixture. In this case, the density and strength of specimens are higher than the corresponding ones obtained after static pressing for the same dwell time. This effect is enhanced with increasing Al 2O 3 percentage. A static pressure approximately 50–80% larger than the cyclic one is required to achieve the same density. Moreover, the strength of compacts with high Al 2O 3 content is substantially higher after cyclic pressing than under static pressing. The ejection force is higher after cyclic compaction at a given pressure level owing to the higher density achieved.

Measurements of the dynamic elastic moduli of viscoelastic materials with micro-inclusions

An indirect method has been proposed [see J. Acoust. Soc. Am. 102, 3549–3555 (1997)] to determine the complex, frequency-dependent, elastic moduli of polymers containing microscopic inclusions from laser-based measurements and finite element modeling. The method consists in measuring the surface dynamics of the sample under harmonic excitation by noncontact laser Doppler interferometry. The experimental results are then matched with numerical predictions in which the moduli are the adjustable parameters. The method is first validated at ambient pressure by measuring the dynamic moduli of a sample of known properties. Results obtained with samples of the same voided viscoelastic material but with different aspect ratios are presented. To assess the effect of static pressure on the moduli, the sample is placed inside a static pressure air chamber (0–500 psi) and the effect of pressure cycling is investigated by measuring the moduli during the first pressure cycle (0–500, and 500–0 psi) and after eight pressure cycles. [Work supported by ONR, code 334.]

Kinetic Parameters for Pressure-Temperature Inactivation of Bacillus subtilis α-Amylase under Dynamic Conditions

Pressure-temperature inactivation kinetics of two enzymatic model systems based on Bacillus subtilis α-amylase (BSA), previously determined under isobaric-isothermal conditions, were studied under more realistic, i.e. dynamic, process conditions. The proposed kinetic model was found to accurately describe non-isobaric/non-isothermal inactivation of BSA in absence as well as in presence of 15% glycerol. Furthermore, the effect of pressure cycling on the inactivation of BSA (in absence of glycerol) was investigated. Multiple application of pressure seemed to exert a more pronounced inactivation effect as compared to a single-cycle process of the same total time. This additional effect, however, could be completely attributed to the more extensive temperature variation occurring during pressure cycling.

Densification of composite powder compacts in pressure cycling

The effect of pressure cycling on the consolidation of green composites from powders is investigated. Mixed powders of lead and various amounts of alumina were consolidated under static and cyclic pressure at room temperature in constrained “uniaxial” consolidation experiments. The experiments show that in static compaction, density dramatically decreases with increasing ceramic content. In a separate series of experiments, the compacts were subjected to a large number of loading cycles where the pressure varied from zero to a constant maximum value. Virtually identical results are obtained when the powder mixtures were dilute in ceramic. However, at high ceramic contents much higher densities were obtained in stress cycling. Increasing the compaction pressure cycle amplitude and the number of cycles significantly increases the compacted density, but changes in the frequency have relatively little effect at the same number of cycles. Green composites fabricated with cyclic pressure also have significantly increased hardness and rupture strength relative to those produced in static compaction. The improved consolidation is explained and qualitatively analyzed in terms of the volumetric mismatch between the metal and ceramic that is naturally produced in a pressure change. This produces deviatoric stresses in the metal phase. These in turn facilitate plastic deformation and consolidation. This effect of volumetric mismatch creating deviatoric stresses which aid plastic flow and, hence, densification is believed to be quite general.

Sputtered thin-film strain gauges for differential pressure measurement

A differential pressure transducer with sputtered gold films as strain gauges has been designed and fabricated. The construction details of the sensing element assembly are given. The details of the strain gauge film configuration employed and the thin-film deposition process are also presented. Information on the output characteristics of the differential pressure transducer such as effect of pressure cycles on output, thermal stability, bidirectional calibration results obtained and individual gauge stability is reported.

Effects of room-temperature pressure cycling on the critical currents in a YBa2Cu3O7−δ superconductor

We have studied the effects of sequential pressure cycling (0–2.8 GPa at room temperature) on the critical currents in a YBa2Cu3O7−δ superconductor. From both low- (0–100 Oe) and high- (up to 5.5 T) field dc magnetic data we identify the contributions to the total critical currents arising from inter- (transport) and intragranular aspects of the superconductor. In our studies, we find that above the pressure limit (≤1.0 GPa) of reversible changes the transport critical current is found to irreversibly decrease by as much as 40%–50% for cycling at 2.8 GPa. However, the intrinsic contribution to the critical current is unaffected. Concomitantly two lower critical fields H*c1 and Hc1 are found necessary to fully characterize the low-field hysteretic loops for these superconductors. One consequence of pressure cycling is that we find H*c1, which signifies the intergranular connectivity, is reduced to lower values. The effects of pressure cycling on the real and imaginary (lossy) components, χ′(T) and χ″(T), of the low-field ac susceptibility are found to be consistent with the dc data.

Effect of Pressure Cycles and Dissolved Air on the Viscosity of Water

Relative measurements on deaerated and air‐saturated water with a sensitivity of about 0.1% show that its viscosity is unaffected by pressure cycles (absence of long‐time relaxation) or the dissolution of air in it, the effect, if any, being less than the sensitivity of the instrument.