Several Hundreds Of Cycles Research Articles

Tracking the Lifecycle of a 21700 Cell: A 4D Tomography and Digital Disassembly Study

Extending the lifetime of commercial Li-ion cells is amongst the most important challenge to facilitate the continued electrification of transport as demonstrated by the substantial volume of literature dedicated to identifying degradation mechanisms in batteries. Here, we conduct a long-term study on a cylindrical Li-ion cell, tracking the evolution of the structure of the cell using X-ray computed tomography. By evaluating the internal geometry of the cell over several hundreds of cycles we show a causal relationship between changes in the electrode structure and the capacity fade associated with cell ageing. The rapid aging which occurs as cells reach their end-of-life condition is mirrored in a significant acceleration in internal architecture changes. This work also shows the importance of consistent and accurate manufacturing processes with small defects in the jelly-roll being shown to act as nucleation sites for the structural degradation and by extension capacity fade.

Co-doping studies to enhance the life and electro-chemo-mechanical properties of the LiMn2O4 cathode using multi-scale modeling and neuro-computing techniques.

A number of engineered cathode materials with longer life cycles and better electro-chemo-mechanical properties can be obtained by partially replacing some of the elements with other relevant ones without compromising much with the structure. To design such superior cathode materials, in this work, we replace a small number (5% or 10%) of Mn3+, with one of the following elements: aluminium, nickel, magnesium, gallium, chromium, and yttrium. Additionally, S2- and F- were used to replace some (∼1%) of the O2- ions (anion) in the crystal. In this work, we have used a combination of Quantum Mechanics (QM), Classical Molecular Dynamics (CMD), Neural Network (NN) and Computational Fluid Dynamics (CFD) modeling. QM has been used to validate the Classical Molecular Dynamics (CMD) simulation results for engineered structures where experimental data are not available. CMD simulations are used to obtain material properties such as lattice expansion, Young's modulus, and diffusion coefficients for un-doped, doped and co-doped structures. NN modeling was used to reduce the computational time to evaluate millions of possible crystal configurations. Finally, the impact of co-doping strategies at the macroscale has been studied using CFD simulations. As a first step, we employed neuro-computing techniques to identify the optimum ionic configuration for all crystal structures, saving ∼88% of the computational time. Next, molecular scale simulations were performed to study the material properties. Molecular dynamics (MD) modeling findings suggest that the relative volume expansion between the fully charged and discharged states of the battery can be reduced by ∼1.9% to ∼2.25%, indicating an improvement in the life of the cathode material by several hundreds of cycles. Findings from both QM and CMD simulations suggest that for these novel engineered materials, electro-chemo-mechanical properties, such as ionic mobility, chemical diffusion coefficient and elasticity, improved. Furthermore, CMD simulations showed that the inter-ionic space between doped metal ions and oxygen is smaller compared to the spacing between Mn3+-O2- in the original LMO spinel, indicating an improvement in the material's structural strength along with the total number of the discharge cycle. Finally, macro scale computational modelling results show that chances of thermal runaway can be reduced significantly for some of the co-doped structures since the intercalation induced maximum stress is lower.

The electro-chemical properties and intercalation mechanism of low strain Li2TiO3 as a high-performance anode material for lithium-ion batteries

In this article, the sol-gel synthesized β-Li2TiO3, referred to as sg-β-Li2TiO3, exhibits superior electro-chemical performance, compared with the theoretical specific capacities of frequently investigated Titanium based oxides, for example, LiTiO2 (143 mAh g-1), Li4Ti5O12 (175 mAh g-1) and Li2Ti3O7 (198 mAh g-1). It delivers a considerable specific capacity of more than 200 mAh g-1 within 100 cycles and close to 200 mAh g-1 after 200 cycles and preserves coulombic efficiency above 97% for all the cycles. After more than 500 cycles, the reversible specific capacity of sg-β-Li2TiO3 is more than 170 mAh g-1 and a less than 2% capacity degeneration is observed for the followed several hundreds of cycles. DFT calculations and MD simulations show 8 f void mediated diffusion comprise the two dimensional diffusion layer on a-b plane and the neighboring diffusion layers are interconnected by two 8 f voids via a Li2 atom. Low energy barriers and high Li+ activities are observed. Three intermediate phases, corresponding to intercalation level x = 0.5, 0.75 and 0.875 in β-Li2+xTiO3, are identified for the intercalation process with the maximal intercalation level 0.875. Both ex-situ XRD and theoretical calculations reveal low volume change or strain less than 5% in the intercalation process. Also, an insulator-metal transition upon lithiation is observed by the electronic structure analysis.

A Comparative Study of Structural Changes during Long-Term Cycling of NCM-811 at Ambient and Elevated Temperatures

Ni-rich layered oxides, like NCM-811 (Li1+δ[Ni0.8Co0.1Mn0.1]1-δO2), are promising cathode active materials for lithium-ion-batteries used in applications such as portable devices and battery electric vehicles. An increased Ni-content typically allows for a higher reversible lithium usage at a given cell potential, thereby improving the specific capacity. However, pronounced capacity fading, especially at high voltages and elevated temperatures, still leads to a limited cycle life.1 The underlying degradation mechanisms and whether they are due to detrimental reactions in the bulk or at the surface, are still controversially discussed in the literature.2,3 We will show a comparison of two studies investigating the capacity fading of NCM-811/graphite full-cells over several hundreds of cycles at ambient and elevated temperatures. In order to focus on the NCM-811 material, we excluded Li loss at the anode by pre-lithiating the graphite anode. The first study was conducted in-situ with two cells cycled at ambient temperature (≈22°C) over 1000 cycles,4 while in the follow-up study a number of pouch-cells were analyzed after cycling at 45°C for up to 700 cycles. As shown in Figure 1a, all cells were cycled at a C-rate of C/2 in a potential window between 3.0 and 4.5 V vs. a Li reference electrode at both 22°C (black line in Fig. 1a) and at 45°C (blue line in Fig. 1a), with two additional C/10 cycles every 50 cycles in case of the 45°C study (blue dots in Fig. 1a). One cell was disassembled every 150 cycles to conduct ex-situ experiments, such as X-ray powder diffraction (XPD) and impedance spectroscopy. A quantitative correlation between the NCM-811 lattice parameters and the Li amount, xLi, allows for monitoring the different contributions to the capacity loss by XPD.4 In the 22°C study, it was shown that the continuous growth of a resistive surface around the NCM-811 primary particles results in (i) an irreversible capacity loss due to the material lost for its formation, and (ii) in a significant impedance growth. The former is compared for both studies according to our XPD analysis in Figure 1b, showing a clear difference in the progression and in the absolute values, suggesting a more detrimental process to kick-in after ≈550 cycles at 45°C. In contrast to the time consuming XPD analysis, the material loss was also quantified by slow C/50 cycling, a rate which is slow enough to not lead to overpotential induced capacity losses due to the gradual resistance build-up over cycling. Hence, this approach could be verified to be a far more practical method to determine the material loss during cycle-life tests. In addition, the bulk material stability in terms of the Li-Ni mixing was analyzed by Rietveld refinement of the XPD data. In contrast to the study conducted at ambient temperature, where the extent of Ni disorder was observed to remain at an essentially constant value over 1000 cycles, it was found to clearly increase when cycling the cells at 45°C over 700 cycles (see Figure 1c).In conclusion, we can state that at both temperatures a resistive surface layer is formed, suggesting that future research should focus on stabilizing the surface of Ni-rich materials. In addition to this surface process, the bulk stability of NCM-811 is altered at elevated temperatures, which is manifesting itself in an increasing Ni disorder.Figure 1:Comparison of data obtained from NCM-811/graphite pouch-cells cycled at ≈22°C (black symbols) and at 45°C (blue symbols) between 3.0 and 4.5 V vs. Li+/Li (controlled vs. Li reference electrode) at the indicated C-rates. (a) Discharge capacity of two exemplary cells, (b) relative material loss of the NCM-811 calculated from XPD analysis, (c) Ni disorder determined via XPD of harvested electrodes after cycling to the indicated cycle number at 45°C (error from calculating the average of two independent measurements).Acknowledgement:This work is financially supported by the BASF SE Network on Electrochemistry and Battery Research.

Multilayer Metal‐Oxide Memristive Device with Stabilized Resistive Switching

AbstractVariability of resistive switching is a key problem for application of memristive devices in emerging information‐computing systems. Achieving a stable switching between the nonlinear resistive states is an important task on the way to implementation of large memristive cross‐bar arrays and solving the related sneak‐path‐current problem. A promising approach is the fabrication of memristive structures with appropriate interfaces by combining the materials of electrodes with certain oxygen affinity and different dielectric layers. In the present work, such approach allows the demonstration of stabilized resistive switching in a multilayer device structure based on ZrO2(Y) and Ta2O5 films. It is established for the large‐area devices that the switching is stabilized after several hundreds of cycles. A possible scenario of the stabilization is proposed taking into account experimental data on the presence of grain boundaries in ZrO2(Y) as the preferred sites for nucleation of filaments, self‐organization of Ta nanocrystals as the electric field concentrators in Ta2O5 film, as well as oxygen exchange between oxide layers and interface with bottom TiN electrode. The robust resistive switching between nonlinear states is implemented in microscale cross‐point devices without numerous cycling before stabilization promising for the fabrication of programmable memristive weights in passively integrated cross‐bar arrays.

Negative Electrodes for Lithium-Ion Batteries Obtained by Photoanodization of Solar-Grade Silicon

Negative electrodes for lithium-ion batteries prepared by electrochemical etching of single-crystalline silicon crystals demonstrate a high specific capacity per gram of the material and per unit of nominal anode area as well as a high stability during several hundreds and even thousands of cycles. However, industrial application of such structures is inexpedient in view of the high cost of the material and technology used. In this work we have investigated anodes based on disordered macropores in solar-grade n-Si obtained by photoanodization in a 4% HF solution in dimethyl formamide. The use of this organic electrolyte leads to the formation of layers with a porosity higher than in an aqueous electrolyte and ensures spontaneous separation of these layers from the substrate. The anodes have been prepared from macroporous membranes with a thickness of 48–86 μm and a porosity of 52–75%, and their electrochemical parameters have been studied. It is found that the geometrical parameters of the porous structure and experimental conditions determine the charge and discharge capacity and the cycle life of the anodes. In the regime of the charge capacity limited by 1000 mA h/g and charge/discharge rate C/5, the obtained anodes can stably operate during several hundreds of cycles, preserving a high (greater than 98%) Coulombic efficiency.

Thermomechanical simulation of flat tiles mock-ups under high heat flux

In the WEST (W -for tungsten- Environment in Steady-state Tokamak) tokamak, an actively cooled tungsten divertor for testing high heat flux technology is implemented. Beside the presently tested ITER divertor technology (i.e. W-monoblock), the WEST team in collaboration with ASIPP (China) worked on the development of an alternative design for actively cooled W/Cu plasma facing components capable to sustain heat loads close to monoblock design. Within this framework, two small-scale mock-ups based on the W-armoured flat-tile concept were produced by ASIPP and successfully tested in the electron beam facility JUDITH-1 (FZ-Jülich, Germany) under successive thermal cycling at 10, 15 then 20 MW/m². These results showed the capacity of this technology to remove heat loads over several hundreds of cycles at 20 MW/m2 without obvious indication of damage impacting the heat exhaust capability. However, the post-mortem analysis showed crack formation perpendicular to the loaded surface proceeding into the pure Cu interlayer for those tiles tested at 20 MW/m². This contribution focuses on the thermal and structural analysis performed with ANSYS for these components. The convective heat transfer coefficients were calculated using the Nukiyama model and the mechanical properties of pure copper at high temperature were extrapolated using the Ramberg-Osgood model. The thermal results are in good agreement with the experiments. The thermo-mechanical simulation explains partially the defects observed on the mocks up with the selected approach, which leads to suggest improvements for further study by modelling kinematic hardening for tungsten and creep for oxygen-free copper.

Отрицательные электроды для литий-ионных аккумуляторов, полученные фотоанодированием кремния солнечной градации

AbstractNegative electrodes for lithium-ion batteries prepared by electrochemical etching of single-crystalline silicon crystals demonstrate a high specific capacity per gram of the material and per unit of nominal anode area as well as a high stability during several hundreds and even thousands of cycles. However, industrial application of such structures is inexpedient in view of the high cost of the material and technology used. In this work we have investigated anodes based on disordered macropores in solar-grade n -Si obtained by photoanodization in a 4% HF solution in dimethyl formamide. The use of this organic electrolyte leads to the formation of layers with a porosity higher than in an aqueous electrolyte and ensures spontaneous separation of these layers from the substrate. The anodes have been prepared from macroporous membranes with a thickness of 48–86 μm and a porosity of 52–75%, and their electrochemical parameters have been studied. It is found that the geometrical parameters of the porous structure and experimental conditions determine the charge and discharge capacity and the cycle life of the anodes. In the regime of the charge capacity limited by 1000 mA h/g and charge/discharge rate C /5, the obtained anodes can stably operate during several hundreds of cycles, preserving a high (greater than 98%) Coulombic efficiency.

Qualification and post-mortem investigation of actively cooled tungsten flat-tile mock-ups for WEST divertor

The WEST (W – for tungsten – Environment in Steady-state Tokamak) project has provided the opportunity of to developing and qualifying, in collaboration with ASIPP (China) and FZJ (Germany) a newly attractive W/Cu actively cooled PFCs technology able to sustain high heat loads close to ITER divertor ones.Within this framework, ASIPP has produced two small-scale mock-ups based on the W-armoured flat-tile concept. The results presented herein focus on the qualification program, performed by CEA, which consisted in a preliminary non-destructive testing (NDT) control based on infrared thermography to assess the joint interface quality followed by cyclic high heat flux (HHF) testing performed at FZJ. The HHF testing, performed by successive thermal cycling, allowed demonstrating the thermal performance of this technology to remove heat loads over several hundreds of cycles at 20 MW/m2 without obvious indication of damage impacting the heat exhaust capability for both mock-ups.Furthermore, the subsequent post-mortem microstructural analysis allowed confirming the issues regarding the induced fatigue damages, especially the tungsten crack formation perpendicular to the incident surface appeared during cycling at 10 MW/m2 and plastic deformation inducing microstructure evolution in the pure Cu-interlayer during cycling beyond 10 MW/m2 for both mock ups.

Spectroscopic Characterization of the SEI Layer Formed on Lithium Metal Electrodes in Phosphonium Bis(fluorosulfonyl)imide Ionic Liquid Electrolytes.

The chemical composition of the solid electrolyte interphase (SEI) layer formed on the surface of lithium metal electrodes cycled in phosphonium bis(fluorosulfonyl)imide ionic liquid (IL) electrolytes are characterized by magic angle spinning nuclear magnetic resonance (MAS NMR), X-ray photoelectron spectroscopy (XPS), fourier transformed infrared spectroscopy, and electrochemical impedance spectroscopy. A multiphase layered structure is revealed, which is shown to remain relatively unchanged during extended cycling (up to 250 cycles at 1.5 mA·cm-2, 3 mA h·cm-2, 50 °C). The main components detected by MAS NMR and XPS after several hundreds of cycles are LiF and breakdown products from the bis(fluorosulfonyl)imide anion including Li2S. Similarities in chemical composition are observed in the case of the dilute (0.5 mol·kg-1 of Li salt in IL) and the highly concentrated (3.8 mol·kg-1 of Li salt in IL) electrolyte during cycling. The concentrated system is found to promote the formation of a thicker and more uniform SEI with larger amounts of reduced species from the anion. These SEI features are thought to facilitate more stable and efficient Li cycling and a reduced tendency for dendrite formation.

Enhancement of a CaO/Ca(OH)2 based material for thermochemical energy storage

The application of hydration/dehydration reactions of CaO/Ca(OH)2 to thermochemical energy storage systems can be facilitated by the development of Ca-based materials with improved mechanical properties when compared to the natural Ca-precursor, while maintaining good chemical activity. For this purpose, we are developing composite materials for fluidized bed or fixed bed applications synthesized using sodium silicate to bind fine CaO/Ca(OH)2 particles. In this work, the mechanism of decay in the mechanical properties of the resulting CaO/Ca-silicates composites over hundreds of hydration/dehydration cycles has been investigated. Based on the observed mechanism, improvements to the method of synthesis of the materials have been introduced, in order to retain the original carbonate grain volumes, which are larger than those of the equimolar quantity of the expanding Ca(OH)2 during hydration. A noticeable improvement in the mechanical stability of the resulting pellets was observed when the material was exposed to temperatures of around 880°C in pure CO2 before calcination in order to avoid the decomposition of CaCO3 during the formation of the hard Ca-silicates that provide mechanical strength to the composite. Further gains in mechanical stability were achieved by avoiding the complete hydration of the CaO grains in the composites. These results confirm the primary role of Ca(OH)2 anisotropic expansion as the main cause of the reduction in crushing strength of the pellets. It can be concluded that the formation of calcium silicates as binders of CaO rich grains is a promising route for the development Ca-based composite materials. However, more effort is still needed to overcome the decay in performance observed after several hundreds of cycles.

Ionic Liquid-Derived Nitrogen-Enriched Carbon/Sulfur Composite Cathodes with Hierarchical Microstructure—A Step Toward Durable High-Energy and High-Performance Lithium–Sulfur Batteries

We describe the preparation of turbostratic carbon in monolithic form by silica template method and its use as host matrix to trap polysulfides in Li–S batteries. The synthesized ionic liquid-derived carbon is hierarchically structured with pore size maxima around 6 nm and 750 nm, and it has a room temperature electrical conductivity of 7–8 S cm–1, owing to a high content of pyridinic and graphitic nitrogen. Further, this carbon can accommodate up to ∼80% sulfur by weight, and the resulting nanocomposite demonstrates promising performance as novel electrode material for Li–S batteries. Cathodes with low areal mass loading (1 mgsulfur cm–2) can be cycled at C/5 and 1C over several hundreds of cycles with low polarization and very little capacity fading (4% between the fifth and 1000th cycles at 1C). Highly loaded cathodes (4 mgsulfur cm–2) also exhibit good cyclability at C/5 with areal capacities of 2.6 mAh cm–2 on average over 200 cycles. Yet the high capacities make the cells more prone to electrolyte d...

A viscoplastic model for rate-dependent hardening for asphalt concrete in compression

This paper presents a new type of viscoplastic model based on viscoelastic convolution integrals for explaining the behavior of asphalt concrete in compression under repeated loading. Triaxial compression cyclic tests carried out for long rest periods, with different loading times and two different pulse shapes, square and haversine, were used in developing and validating the model. These tests demonstrate that the evolution of permanent deformation depends on load history. This history-dependent behavior is not captured accurately by some of the existing Perzyna-type viscoplastic models in which permanent deformation evolution depends on the current values of stress and viscoplastic strain. Therefore, in this study, viscoelastic-like convolution integrals were used in the model to capture the effect of history. The proposed model is applicable to compressive creep and recovery experiments at 54°C with (1) several hundreds of cycles of loading including the secondary creep region, (2) haversine loading shapes at three different peak deviatoric stress levels, 620kPa, 827kPa, and 1034kPa, and square loading shapes at 827kPa peak deviatoric stress, and (3) long rest periods that allow complete viscoelastic recovery.

Effects of SiO2 and TiO2 on resistance stabilities of flexible indium-tin-oxide films prepared by ion assisted deposition

Inorganic buffer layers such as SiO2 or TiO2 and transparent conductive indium-tin-oxide (ITO) films were prepared on polyethylene terephthalate (PET) substrates by ion assisted deposition (IAD) at room temperature, and the effects of SiO2 and TiO2 on the bending resistance performance of flexible ITO films were investigated. The results show that ITO films with SiO2 or TiO2 buffer layer have better resistance stabilities compared to ones without the buffer layer when the ITO films are inwards bent at a bending radius more than 1.2 cm and when the ITO films are outwards bent at a bending radius from 0.8 cm to 1.2 cm. ITO films with SiO2 buffer layer have better resistance stabilities compared to ones with TiO2 buffer layer after the ITO films are bent several hundreds of cycles at the same bending radius, for the adhesion of SiO2 is stronger than that of TiO2. The compressive stress resulted from inward bending leads to the formation of more defects in the ITO films compared with the tensile stress arising from outward bending. SiO2 and TiO2 buffer layers can effectively improve the crystallinity of ITO films in (400), (440) directions.

Metal Alloy Electrode Configurations For Advanced Lithium‐Ion Batteries

AbstractWe show that the proper use of lithium‐metal (Li‐M) alloys as electrodes in lithium cells requires formulations capable of maintaining their integrity upon cycling. A very effective one is based on the dispersion of nanosized metal particles within a carbon matrix in order to form M‐C composites. The validity of this strategy has been demonstrated in the cases where M is Sn and Sb, respectively. Tests in lithium cells demonstrate that the Sn‐C composite electrodes have a specific capacity much higher than that of commercial graphite, i.e. 500 mAhg–1 versus 370 mAhg–1, and that this high value is kept unchanged for several hundreds of cycles. The Sb‐C composite electrode has an intrinsic capacity lower than that of the Sn‐C one; however, also in this case, the capacity delivery remains stable for many cycles, thus confirming the unique role of the carbon matrix in stabilising the electrode structure. The investigation of the Li‐M alloy electrodes has been extended to Sn‐Co‐C ternary systems which supposedly are similar to that used as anode in a recently released commercial battery. Also, these electrodes show favourable cycling characteristics, although some questions still remain on the capacity retention upon prolonged cycling.

In Vitro Bioactivity of Atomic Layer Deposited Titanium Dioxide on Titanium and Silicon Substrates

A non-bioactive implant device can easily be changed to in vitro bioactive with a thin coating of crystalline TiO2. This crystalline coating can be deposited very thin with great step coverage at a low temperature with Atomic Layer Deposition (ALD). An anatase TiO2 coating was built up atomic layer by atomic layer using TiI4 and H2O as precursors in a hot wall furnace. Several hundreds of cycles resulted in a 10-30nm well defined TiO2 of anatase phase on both Si and Ti substrates. These coatings were shown to be bioactive when immersed in simulated body fluid in vitro, as hydroxyapatite (HA) formed on the surface. The surface roughness of the substrates affected the adhesion of the HA. The adhesion was low on the smooth Si but much better on the 100 times rougher Ti. The ALD technique is promising for coating substrates of all shapes with bioactive crystalline TiO2 at a low temperature.

Metastable effects on martensitic transformation in SMA

The efficiency of shape memory alloy (SMA) as damper and/or standard actuator is truly enhanced when the material can be cycled without any relevant accumulation of the permanent deformation (i.e. under 0.5% for several hundreds of cycles). The particular properties of the CuAlBe alloy permit relevant grain growth with reasonable reduction of mechanical properties (from 300-350 to 250-300 MPa at fracture). Samples prepared with an appropriate heat thermal treatment (HIT) and relevant mean diameter of grain avoids accumulative deformation for series of cycles (near 500) up to 3.5% of deformation. The analysis of different wires of CuAlBe alloy shows, in the first part of HIT, a proportionality between the grain surface and the time at 1123 K. In the last part of the HTT the grain growth shows an increased complexity related with interactions between the grain boundaries and the external surface of the samples.

Nanostructured mesoporous carbon as electrodes for supercapacitors

Symmetrical carbon/carbon double layer capacitors (EDLCs) were fabricated employing nanostructured mesoporous nongraphitized carbon black (NMCB) powders and their EDLC behavior was studied using electrochemical techniques viz., cyclic voltammetry, a.c.-impedance, and constant current cycling. Rectangular shape cyclic characteristics were observed indicating the double layer behavior of the NMCB carbon electrodes. The mechanism of double layer formation and frequency dependent capacitance were deduced from the ac-impedance analysis. Specific capacitance, power density and energy density were derived from constant current charge/discharge measurements. NMCB powders demonstrated a specific capacitance of about ∼39 F g −1 and the power density of 782 W kg −1 at a current density of 32 mA cm −2. Nevertheless, at a low current density (3 mA cm −2), the specific capacitance of ∼44 F g −1 was achieved, which corroborates with the values obtained by means of ac-impedance (40 F g −1) and cyclic voltammetry (41.5 F g −1). The test cells demonstrated the stable cycle performance over several hundreds of cycles.

A solid polymer electrolyte-based ethanol gas sensor

Platinum-based membrane-electrode assemblies have been prepared to make electrochemical measurements of breath alcohol levels. Measurements are made by using a solid polymer electrolyte ethanol-air fuel cell. A diffusion membrane is placed in the feed compartment to limit the cell response by ethanol diffusion. The cell is found suitable for the realization of gaseous ethanol sensors. Reproducible cell responses are obtained over several hundreds of cycles. The cell current is proportional to the ethanol concentration in the feed compartment and to the thickness of the diffusion membrane. The transient response of the cell is simulated using Fickian phenomenological equations. Calculated results are in good agreement with experimental data.

The effect of proof testing on the shakedown behaviour of pressure vessel nozzles

Cyclic internal pressure tests were conducted over several hundreds of cycles at pressures up to and in excess of the calculated proof test pressure on two nominally ‘identical’, stainless steel type 316 flush 90 degrees pressure vessel nozzles, designed and manufactured to BS 5500. Prior to this pressure cycling, one vessel was subjected to the required proof test of 1.25 times the design pressure. Significant incremental straining was recorded in the non-proof tested vessel during cycling at all pressures above the first yeild pressure (0.336 × design pressure). For the proof tested vessel significant incremental straining was not recorded during cycling until 15 percent above the design pressure.