Propagation Rate Research Articles

Heterogeneity induced fracture characterization of concrete under fatigue loading using digital image correlation and acoustic emission techniques

Understanding the fatigue failure mechanisms in concrete is complex and remains an area of ongoing investigation. Material heterogeneity, along with the size effect, plays a significant role in specifying the crack propagation behaviour and fatigue life in case of repetitive loading conditions. In this study, the influence of material heterogeneity on the fatigue behaviour of concrete has been examined. Three different-size beam specimens with varying heterogeneity (aggregate sizes) have been considered to investigate various fracture characteristics under repetitive load conditions. Acoustic emission and digital image correlation techniques have been employed to analyse crack growth behaviour. The results revealed that stiffness degradation and crack propagation rates are faster for the specimens with smaller aggregate sizes compared to the larger aggregate size specimens of the same depth. Moreover, the fatigue life and effective crack length at failure are also higher in the case of larger aggregate sizes compared to smaller ones. Therefore, a heterogeneity-adjusted, analytical model of fatigue crack growth has been proposed. Further, the AE parameters have been utilized to characterize the tensile and shear crack dominance in different stages of fatigue crack propagation. The outcome of this study can be utilized to anticipate the crack propagation behaviour and residual fatigue life for any combination of specimen size and aggregate size.

Slow recovery rates and spatial aggregation of Triatoma infestans populations in an area with high pyrethroid resistance in the Argentine Chaco

BackgroundThe emergence of pyrethroid resistance has threatened the elimination of Triatoma infestans from the Gran Chaco ecoregion. We investigated the status and spatial distribution of house infestation with T. infestans and its main determinants in Castelli, a municipality of the Argentine Chaco with record levels of triatomine pyrethroid resistance, persistent infestation over 2005–2014, and limited or no control actions over 2015–2020.MethodsWe conducted a 2-year longitudinal survey to assess triatomine infestation by timed manual searches in a well-defined rural section of Castelli including 14 villages and 234 inhabited houses in 2018 (baseline) and 2020, collected housing and sociodemographic data by on-site inspection and a tailored questionnaire, and synthetized these data into three indices generated by multiple correspondence analysis.ResultsThe overall prevalence of house infestation in 2018 (33.8%) and 2020 (31.6%) virtually matched the historical estimates for the period 2005–2014 (33.7%) under recurrent pyrethroid sprays. While mean peridomestic infestation remained the same (26.4–26.7%) between 2018 and 2020, domestic infestation slightly decreased from 12.2 to 8.3%. Key triatomine habitats were storerooms, domiciles, kitchens, and structures occupied by chickens. Local spatial analysis showed significant aggregation of infestation and bug abundance in five villages, four of which had very high pyrethroid resistance approximately over 2010–2013, suggesting persistent infestations over space-time. House bug abundance within the hotspots consistently exceeded the estimates recorded in other villages. Multiple regression analysis revealed that the presence and relative abundance of T. infestans in domiciles were strongly and negatively associated with indices for household preventive practices (pesticide use) and housing quality. Questionnaire-derived information showed extensive use of pyrethroids associated with livestock raising and concomitant spillover treatment of dogs and (peri) domestic premises.ConclusionsTriatoma infestans populations in an area with high pyrethroid resistance showed slow recovery and propagation rates despite limited or marginal control actions over a 5-year period. Consistent with these patterns, independent experiments confirmed the lower fitness of pyrethroid-resistant triatomines in Castelli compared with susceptible conspecifics. Targeting hotspots and pyrethroid-resistant foci with appropriate house modification measures and judicious application of alternative insecticides with adequate toxicity profiles are needed to suppress resistant triatomine populations and prevent their eventual regional spread.Graphical

From Pre‐Darcy Flow to Darcy Flow in Porous Media: A Simple Unified Model

AbstractExtensive experiments have demonstrated that fluid flow in low‐permeability media deviates from Darcy's law at low pressure gradients, which is called pre‐Darcy flow. Although numerous pre‐Darcy flow models have been proposed, these models generally contain one or more empirical parameters with no clear physical meaning. In this paper, we present a simple unified model to describe pre‐Darcy flow in porous media by introducing the concept of loss permeability. The physical meaning of the loss permeability parameter and its relationship to permeability are analyzed. Based on the statistics of the loss permeability parameter results of 24 core samples, we found that there is a good positive correlation between the loss permeability parameter and the absolute permeability. A smaller loss permeability indicates a stronger fluid‐solid interaction and a stronger nonlinearity between the flow velocity and the pressure gradient. Taking a one‐dimensional linear unsteady flow of a slightly compressible fluid in a homogeneous porous medium as an example, we solve the pressure diffusion equation based on the proposed model using a finite difference method. Our results demonstrate that the rate of pressure propagation for pre‐Darcy flow is slower than that for Darcy flow for the entire observation period, which corrects previous conclusions. This study is highly important for improving the understanding of fluid flow in low‐permeability media.

High-pressure corrosion fatigue experiments employing diverse methodologies for assessing rates of crack propagation

The new extreme faces strain gauges (XFS) technique, when compared to the direct current potential drop (DCPD) and back face strain gauge (BFS) methods, has shown superior accuracy and reliability in studying corrosion fatigue in high pressure. The XFS method serves a dual purpose by accurately measuring the crack length and acting as a mechanical load transducer. The results indicate that all three techniques can predict the final crack length effectively. However, BFS is unsuitable for high-pressure environments, and the current DCPD method can affect the crack propagation rate. The developed XFS methodology shows excellent performance in accurately evaluating corrosion fatigue studies.

Scapular morphology does not predict supraspinatus tendon tear propagation following an individualised exercise therapy programme.

To determine whether scapular morphology could predict isolated supraspinatus tendon tear propagation after exercise therapy. We hypothesised that a larger critical shoulder angle (CSA) and type III acromial morphology predict a positive change in tear size. Fifty-nine individuals aged 40-70 years with isolated symptomatic high-grade partial or full-thickness supraspinatus tendon tears were included. Individuals participated in a structured, individualised 12-week exercise therapy programme and underwent ultrasound to measure tear size at baseline and 12 months following therapy. Computed tomography images were segmented to create three-dimensional subject-specific bone models and reviewed by three trained clinicians to measure CSA and to determine acromion morphology based on the Bigliani classification. A binary logistic regression was performed to determine the predictive value of CSA and acromion morphology on tear propagation. The CSA was 30.0 ± 5.4°. Thirty-one individuals (52.5%) had type II acromial morphology, followed by type III and type I morphologies (25.4% and 22.0%, respectively); 81.4% experienced no change in tear size, four (6.8%) individuals experienced tear propagation and seven (11.9%) individuals had a negative change in tear size. No significant difference in tear propagation rates based on CSA or acromion morphology (not significant [NS]) was observed. The model predicted tear size status in 81.4% of cases but only predicted tear propagation 8.3% of the time. Overall, CSA and acromion morphology only predicted 24.3% (R 2 = 0.243) of variance in tear propagation (NS). CSA and acromion morphology were NS predictors of tear propagation of the supraspinatus tendon 12 months following an individualised exercise therapy programme. II.

Atomic simulations of crack propagation in Ni-Al binary single crystal superalloy with a central crack

Nickel (Ni)-based single-crystal superalloys are of great importance in the aircraft industry due to their excellent mechanical properties, and cracks as unavoidable defects may affect the mechanical performances of materials dramatically. In this paper, large scale molecular dynamics (MD) simulations are carried out to understand the deformation mechanisms of Ni-based single crystal with a central crack under tension. Here, the effects of matrixes (γ, γ′ and γ/γ′), strain rates (1 × 109 s−1 ∼ 3 × 109 s−1) and temperatures (300 K∼900 K) on the role of crack propagation are considered. It is observed that dislocations and slip systems in the γ′ model are concentrated near the crack, resulting in the rapid expansion of dislocation, which leads to the fastest crack growth speed and early fracture. While the crack propagation rate of γ and γ/γ′ models are relatively slow, due to the combined action of the Lomer-Cottrell lock and stacking fault tetrahedron structure and Stair-rod dislocation, which hinders crack propagation. In addition, deformation at increased strain rates and/or reduced temperatures, lead to superior yield stress and Young′s modulus for models with a central crack at γ/γ′ interface. On the other hand, high temperature and high strain rate will promote crack propagation in the γ phase, and the higher the strain rate and/or temperature, the faster the crack propagation speed will be. These results will enrich our understanding on the crack propagation and evolution mechanisms in Ni-based single crystal superalloy.

Three Dimensions of<b></b> Fan Reconnection

Many celestial occurrences, including solar flares and the solar corona and modifications to the magnetosphere of Earth, are thought to be caused by the reconnection process. This process occurs in highly conductive plasmas. One of the candidate places for this process is the three-dimensional zero points, in this process, stored energy is transformed into new types of energy Aims. Magnetic reconnection at a single null point: influence of magnetic field symmetry. Methods. We discussed a stable solution to several of the resistivity MHD formulations. Results. The field's asymmetry (k) may impact the propagation area dimensions and rate of reconnection in a variety of ways, depending on the parameters we choose.

Analysis of strength size effect and failure mechanism of asphalt mixtures based on discrete element method

The purpose of this study is to further investigate the strength size effect and failure mechanism of asphalt mixtures and clarify the strength parameter conversion relationship between standard and non-standard size samples. The article established an improved microscopic model for uniaxial compression and indirect tensile testing of asphalt mixtures based on laboratory and discrete element simulation tests. The effects of thickness and gradation on the uniaxial compressive strength (UCS) and indirect tensile strength (ITS) of asphalt mixtures were studied. The loading rates of the UCS and ITS tests were set at 2 mm/min and 50 mm/min, respectively. Additionally, the tensile-compressive stress distribution, crack propagation, and strength contribution rates of different contact types within the sample were investigated during the virtual model loading process. The reliability of the model was validated through laboratory test results. Finally, the strength parameter conversion relationship between standard and non-standard size samples was investigated. The study found that the UCS of asphalt mixtures decreases with increasing thickness, while the ITS increases with increasing thickness, with average reduction and increase rates of 70.69 % and 24.18 %, respectively. The contact fracture ratio and the strength contribution rate of the aggregate-asphalt mortar contacts both exceed 50 %, indicating that the fracture of these contacts is the primary cause of asphalt mixture failure. The use of small-sized samples instead of standard samples in practical applications is promising. These research work outcomes can serve as a theoretical basis for designing asphalt pavement materials and acquiring existing asphalt pavement material parameters.

A Study on the Propagation of Chloride-Induced Stress Corrosion Cracking for Austenitic Stainless Steel at Corrosion Environment

Austenitic stainless steels have been widely used in the petrochemical industry, nuclear power plants and the ship industry due to their high toughness and corrosion resistance. However, these materials are susceptible to environmentally-assisted degradation, such as chloride-induced stress corrosion cracking (CISCC). In this respect, this study investigated CISCC crack propagation rate for austenitic stainless steels, such as type 304L and type 316L, in the corrosion environment. Considering the environment of the spent nuclear fuel canister used in the dry storage system, the test chamber is always maintained at 3.5% NaCl and related humidity (RH) 95% at 60℃. For initiation of CISCC, a test procedure, which has nine pre-cracking procedures for a CT specimen, is suggested. In a test procedure, crack transitioning, which induces the environmental corrosion crack, is observed after mechanical precracking. To determine the CISCC crack length corresponding to each test step, the direct current potential drop (DCPD) method is measured in real-time. In addition, the CISCC crack observed after final fracture is measured using optical microscopy in order to improve the accuracy of the measured crack length. In the test results, CISCC crack resistance of type 316L is better than that of type 304L. Finally, the test results show that the CISCC crack propagation rate is 2.784E-11 m/s for type 304L and is 9.93E-11 m/s for type 316L.

The Suppression Effect of Water Mist Released at Different Stages on Lithium-Ion Battery Flame Temperature, Heat Release, and Heat Radiation

Thermal runaway (TR) is a serious thermal disaster that occurs in lithium-ion batteries (LIBs) under extreme conditions and has long been an obstacle to their further development. Water mist (WM) is considered to have excellent cooling capacity and is widely used in the field of fire protection. When used in TR suppression, WM also exhibits strong fire-extinguishing and anti-re-ignition abilities. Therefore, it has received widespread attention and research interest among scholars. However, most studies have focused on the cooling rate and suppression effect of TR propagation, and few have mentioned the effect of WM on flame heat transfer, which is a significant index in TR propagation suppression. This study has explored the suppression effect of WM released at different TR stages and has analyzed flame temperature, heat release, and heat radiation under WM conditions. Results show that the flame extinguishing duration for WM under different TR stages was different. WM could directly put out the flame within several seconds of being released when SV opened, 3 min after SV opening and when TR ended, and 3 min for WM when TR was triggered. Moreover, the heat radiation of the flame in relation to the battery QE could be calculated, and the case of WM released 3 min after SV opening exhibited the greatest proportion of heat radiation cooling η (with a value of 88.4%), which was same for the specific cooling capacity of WM Qm with a value of 1.7 × 10−3 kJ/kg. This is expected to provide a novel focus for TR suppression in LIBs.

Investigation on the interaction evolution and growth behavior of multiple cracks under fatigue loading

In this study, the cracks interaction is investigated on plates with different crack geometry parameters through finite element analysis and experiments. The presence of multiple cracks may lead to an enhancement or shielding effect on stress intensity factors (SIFs) depending on crack relative positions and sizes, thereby potentially accelerating or decelerating the crack propagation rate. When the crack tips of double parallel non-collinear cracks begin to overlap, the interaction between cracks transitions from an enhancement effect to a shielding effect, and the KII values reach their peak at this point, which are explained by the stress field distributions surrounding the cracks. For non-collinear double cracks with an inclined angle α, the shielding effect of inclined cracks becomes increasingly pronounced in comparison to horizontal cracks as the angle α increases. To verify the numerical results, fatigue crack propagation experiments were carried out on Al–Li alloy samples with double non-collinear cracks with different crack vertical distance. The experimental results show that growth direction of two non-collinear cracks underwent a transition when they overlapped, leading to load mode I changing into mixed mode of I + II. Based on both numerical simulations and experimental results, the material parameters C and m in Paris equation are modified, and then a new method for predicting the multiple cracks growth life is presented. By comparing with the experimental values, it was found that this method exhibits high accuracy and reliability.

Evaluating potential of increasing flow intensity and reducing crevice volume to improve thermal efficiency and hydrocarbon emission in spark-ignition natural gas engines

Low thermal efficiency and high hydrocarbon emissions caused by slow combustion rates and high methane emissions hinder the development of natural gas (NG) engines. Engine structure modifications have always been an important means of improving the combustion effects of engines. This study investigates the effects of combustion chamber improvements on the thermal efficiency and hydrocarbon emissions of stoichiometric spark-ignition NG engines through numerical simulations. The improvements aimed to enhance squish flow, organize high tumble flow, and reduce crevice volume. The results indicate that strengthening the squish intensity by increasing the squish area of the piston can accelerate flame propagation and reduce exhaust loss. However, this improvement is hindered by a significant rise in heat transfer loss, which limits further gains in thermal efficiency. Compared to the traditional high swirl combustion chamber, a high tumble combustion chamber (dual straight intake port combined with a hemispherical piston) can promote flame propagation in the early stages of combustion and increase thermal efficiency by 1.43%. However, the accelerated flame propagation rate resulting from increased flow intensity has little potential to reduce hydrocarbon emissions due to the small contribution of flame quenching to unburned hydrocarbon production. The primary source of hydrocarbon emissions from NG engines is unburned methane in the piston crevice. Therefore, when addressing hydrocarbon emissions from NG engines, the first consideration should be to minimize the volume of the piston crevice, which will significantly reduce methane emissions and incomplete combustion loss.

Improvement of the fatigue life of an electron-beam welded Ti2AlNb joint subjected to an electromagnetic coupling treatment

The local stress concentration created by the seam welding process often reduces the fatigue life of the material along and around the seam. Post-welding heat treatment is usually used to improve the weld performance, but the improvement effect on fatigue life may not be obvious. In this study, a new treatment method of electromagnetic coupling was applied to regulate the Ti2AlNb electron beam weld after heat treatment, so as to improve the fatigue properties of the welded joint. The results show that after electromagnetic coupling treatment, the fatigue limit of the welded joint is increased by 10.4 %, the residual compressive stress is increased, and the fatigue crack propagation rate is decreased. The microstructure analysis shows that after electromagnetic coupling treatment, the fatigue crack source starts in the subsurface layer, the substructural crystals in the fusion zone and the heat affected zone decrease, the recrystallization content and the large angle grain boundary increase, and the dislocation density increases and tends to be homogenized. An increase of at least 2.3 % in hardness of the welded joints also indicates the increase in the dislocation density. Local high density dislocation is found in the grain, which causes dislocation entanglement and hinders crack initiation and propagation and this provides an important basis for improving fatigue properties. This study provides a new method for improving the fatigue properties of Ti2AlNb electron beam welds which can also be used to study the properties of other welded joints.

Fatigue crack propagation anisotropy of an Al–Zn–Mg–Cu super-thick plate

The fatigue crack propagation (FCP) rate is an important performance index in the aerospace industry for the safe lifespan evaluation. In this study, the FCP anisotropy of an Al–Zn–Mg–Cu super-thick rolled plate was analyzed. The results show that as the depth increases, the FCP anisotropy gradually becomes significant especially in the low ΔK region. The specimens tested along the transverse direction exhibit lower FCP rate than those tested along the rolling direction in the low ΔK region, which is related to the difference in the grain shape and grain orientation. More specifically, the crack is easy to deflect along the grain boundaries in the deformed grains when loading along the transverse direction. Meanwhile, more obvious grain orientation deviation on both sides of the crack can cause larger angle deflection, longer FCP path, and lower FCP rate. In the Paris region, the FCP anisotropy is not obvious regardless of thickness. The reason is that the main influencing factor is controlled by strength in this region, while the strength anisotropy is very limited leading to this similarity.

Effect of Mode II in the mixed-mode on the fatigue crack growth behaviour for SAPH440 material

In this study, the effect of mixed-mode loading on fatigue crack growth under varying applied loads for SAPH440 material was experimentally investigated. Previous research has either examined the effect of mixed-mode loading at a fixed angle or its effect on slanted cracks. This paper uses a CTS specimen and a loading device to apply varying angles of load during Mode I loading conditions. Initially, a numerical analysis was performed to validate existing equations for the stress intensity factor, which quantifies the crack driving force in the experiments. In the crack initiation region, load shedding techniques and load increasing techniques were used to confirm fatigue cracking considering mixed-mode effects. The change in the threshold value according to the loading angle was also evaluated. In the crack propagation region, a multi-level loading technique was employed to assess the mixed-mode effects under varying loading angles. This process verified the mixed-mode effect under conditions where the applied load angle varies. The fatigue crack fracture surfaces were examined using digital camera capture and SEM. It was found that when mixed-mode loading occurs during Mode I loading, the fatigue crack propagation rate varies depending on the mixed-mode loading angle.

Investigation on the fatigue crack propagation of rock-concrete interface under fatigue loading below the initial cracking load

The fatigue crack propagation of the composite rock-concrete interface under constant-amplitude flexural fatigue loading below the initial cracking load was investigated in the present study. Fatigue pre-crack initiation and propagation tests were first conducted on three types of rock-concrete interfaces under three-point bend loading. It was shown that for the rock-concrete interface, the damage evolution throughout the fatigue loading process can be divided into deceleration and acceleration stages according to the rate curves of flexural stiffness, deformation and crack propagation. The crack propagation rate exhibited two distinct regions when plotted on a log scale, namely the small-crack growth region and the long-crack growth region. The small-crack growth region for the studied rock-concrete interfaces was not particularly pronounced. The long-crack growth region was the Paris’ law region and included both the acceleration and part of the deceleration stages. Based on the experimental results, the fatigue crack propagation rate in the Paris’ law region was then described using the empirical Paris’ law. The exponent m1 in the Paris’ law was found to be approximately constant, with a value of m1 ≈ 21 for the rock-concrete interface. The pre-factor C1 was found to be dependent on both the load ratio R and the type of the rock-concrete interface (represented by an elastic mismatch parameter α). By introducing R and α into the empirical Paris’ law, an adjusted Paris’ law was proposed. The adjusted Paris’ law can describe the fatigue crack propagation rate in a unified way for the same rock-concrete interface of different R and different interfaces in the scope of this research. Based on the adjusted Paris’ law, the fatigue cycles during the crack propagation and fatigue lifetimes of all tested rock-concrete interface specimens were reasonably predicted. For practical applications, an approach was suggested involving a combination of the adjusted Paris’ law and a material coefficient β (approximately β ≈ 0.143 in this study) to estimate the fatigue lifetimes of structures or specimens with existing pre-cracks at the rock-concrete interface.

Effect of Melatonin on the Growth of Dendrobium officinale Protocorm-Like Bodies

Dendrobium officinale Kimura & Migo is a perennial herbaceous plant of the genus Dendrobium in the family of Orchidaceae with high medicinal value. Melatonin (MT) is an indole-like tryptamine with functions such as regulating plant growth and development. This experiment investigated the effects of different concentrations of MT on the growth and development of protocorms of D. officinale protocorm-like bodies (PLBs). The results showed that the changes in morphological indicators such as color, cluster size, and surface changes were more significant under 75 µM MT than those of 0 µM (CK), and the appearance of white on the PLB surface was expedited, which was more conducive to the proliferation of PLBs. MT treatment of 100 µM inhibited the differentiation of adventitious buds, and the contents of photosynthetic pigments, polysaccharides, and flavonoids were significantly increased. Moreover, as compared with CK, the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) in PLBs increased significantly, while the content of malondialdehyde (MDA) decreased gradually with 75 µM or less. In conclusion, a concentration of 75 µM melatonin can enhance the rapid propagation rate of D. officinale in vitro, providing insights into the effects of melatonin on the growth of tissue-cultured D. officinale seedlings.

Performance of interstitial thermal barrier materials on containing sidewall rupture and thermal runaway propagation in a lithium-ion battery module

Containing thermal runaway propagation in lithium-ion battery packs is a pertinent problem that is exacerbated when considering high energy density batteries and severe battery failure modes, such as sidewall rupture. This work investigates five different passive thermal barrier materials for their performance with respect to containing sidewall rupture and mitigating thermal runaway propagation between high energy density 21,700 cells. Along with propagation rate and total count of sidewall rupture failures, two new key performance indicators are introduced, the temperature reduction value and the sidewall rupture ratio, to quantify a material's performance. Overall, a stainless steel thermal barrier coated with an intumescent flame-retardant fabric performs best out of the five materials investigated. Evidence is given for the count of sidewall ruptures being linearly correlated to the propagation rate. It is shown that cells that fail with sidewall rupture have an average maximum surface temperature of 919 °C compared to 653 °C for cells that fail with top cap rupture. Evidence is also presented that sidewall rupture propagates to adjacent cells in a module. This work aims to provide battery pack designers with information to aid them in determining a strategy for containing thermal runaway propagation and sidewall rupture, including a method to evaluate the performance of thermal barrier materials against this objective.

Flight delay propagation in the multiplex network system of airline networks

The flight delay propagation and recovery processes in airline networks differ due to differences in airline network structures, capacity distributions, and base airport locations. When each airline network is regarded as a network layer, flight delay propagation and interaction in a multiplex network system (MNS) composed of multiple airlines will become more complex and variable. In this paper, flight delays from different airlines are considered propagation sources, and an MNS-based flight delay propagation model is established under the framework of the susceptible-infected-susceptible model. By comparing the independent propagation process of delays in a single-layer airline network and the interactive propagation process of delays in an MNS, we investigate the impact of network structure on flight delays to propose corresponding delay control strategies for different airlines. The results show that unlike in single-layer networks, in an MNS, the behavior of airlines at an airport facilitates or inhibits delay propagation in other layers by influencing the network characteristics and propagation rate. The same airport may even play different roles in different layers, depending on the function it has. Therefore, not all flights are infected or have aggravated delays when accessing the MNS; instead, they are impacted by combined factors such as on-time performance, network structure, and flight interaction.

Effect of trace element arsenic on the high cycle fatigue properties and the carbide uniformity in high carbon chromium bearing steel

AbstractIn this paper, the mechanical properties and microstructures of bearing steels with arsenic contents of 30, 40, and 120 ppm have been investigated. The results show that As‐40 steel has the highest tensile strength but lower fatigue strength than As‐120 steel. The fatigue crack propagation rate of As‐120 steel is relatively low, mainly due to the increase in ΔKth. After quenching and tempering, As‐120 steel has larger prior austenite grains and more undecomposed, elongated carbides appear, reducing the uniformity of the steel. For carbides with an aspect ratio greater than 2, they cannot grow by the Oswald mechanism of spontaneous migration but are spheroidized by self‐cracking. The undissolved elongated carbides have a lower chemical potential, which increases the diffusion tendency of arsenic in the matrix. SIMS and EPMA analyses show that there is no significant distortion of the trace element arsenic.