Compressive Stress Distribution Research Articles

Delamination initiation in fully clamped rectangular CFRP laminates subjected to out-of-plane quasi-static indentation loading

To further investigate the effects of in-plane and out-of-plane stresses on the delamination initiation for composite laminates under out-of-plane loading, this paper reports a joint experimental and numerical study, in which the fully clamped rectangular CFRP composite laminates were subjected to out-of-plane quasi-static indentations. The results show that the combination of the out-of-plane shear and in-plane tensile stresses together determined the initiation of delamination, whereas the influences of the out-of-plane compressive stress on the delamination initiation can be neglected. For the purpose of understanding the effects of deformations on the out-of-plane shear and compressive stress distributions, a concise analytical model was developed, which was validated against the numerical and experimental results. As a key take-away, this study reveals that the common impact tests at the geometric centre of the panel may not resemble sufficient similitude with stiffened panels where panel flexure is suppressed by various geometrical stiffening concepts.

Influence of the attenuation of subgrade elastic modulus caused by precipitation on ballasted track structure

• Developed numerical model of ballasted track-subgrade structure considering precipitation based on FEM/EMLT. • Quantitatively revealed the influence of the subgrade elastic modulus for ballasted track-subgrade structure. • Systematically presented latest materials to improve subgrade waterproofing and drainage performance. Precipitation will cause subgrade elastic modulus ( E s ) to decay as subgrade are composed of fine-grained soil with water sensitivity, resulting in adverse mechanical effects on the ballasted track structure. A numerical model of the ballasted track-subgrade structure was established using the KENTRACK program combining the finite element method (FEM) and elastic multi-layer theory (EMLT), taking into account the non-linearity of the ballast and sub-ballast. The reliability of the developed numerical model was verified macroscopically by a laboratory testing based on vertical compressive stress distribution at the top of subgrade. The mechanical response of the track-subgrade structure and the damage law of the subgrade based on permanent deformation were quantitatively analyzed due to the attenuation of E s . The latest materials for the selection to improve subgrade waterproofing and drainage performance were more systematically presented. The results show that the subgrade surface occurs the stress concentration phenomenon as E s becomes larger, and the subgrade elastic deformation is not sensitive to E s with increasing it to 80 MPa, which the impact mainly appears in the region surrounded by two-axle load and the two rails. In addition, E s decay due to precipitation under constant applied load conditions directly reduces the service life of the subgrade, and the relationship between the allowable number of load repetitions ( N a ) at the top of subgrade and E s can be expressed as a power function. The laying of wicking geotextiles at the top of subgrade, asphalt mixture/PP-modified gravel mixture waterproofing layer, etc. can be utilized to improve the elastic modulus of subgrade due to their excellent waterproofing and drainage performance.

Residual stresses of Q235 steel wallboard - Q460 high-strength steel column structural system

For the wallboard - column structural system on the side of box-type steel structures, the residual stress distribution of the high-strength steel (HSS) column supported by stressed skin wallboards is affected by the welding between columns and wallboards, making it significantly different from an independent welded H-section member. To investigate and model the residual stress in Q235 steel wallboard - Q460 HSS column structural system, to which little attention has been paid, an experimental study was conducted using both the hole-drilling method and sectioning method. The residual stress magnitude and distribution were obtained. Comparison of the two measurement methods indicates that the maximum tensile residual stresses near the welds measured using the hole-drilling method are much greater than those obtained from the sectioning method. The welding between column and wallboards reduces the maximum tensile residual stress in the middle of column rear flange as well as the compressive stress distribution range in the rear flange. The magnitudes of compressive residual stresses decrease with increasing width-to-thickness ratio and component plate thickness, while no significant correlation with geometries was observed for the tensile stresses. The residual stresses in the combination of the rear flange and wallboards, front flange, and web can be regarded as being in self-equilibrium respectively. In addition, a simplified distribution model is proposed and compared with the experimental results. The new stress distribution model can provide a foundation for investigating the buckling behavior of HSS columns supported by stressed wallboards. • Residual stresses in Q235 steel wallboard - Q460 high-strength steel column structural system were measured. • Results obtained by the hole-drilling method and sectioning method were compared. • Effects of welding between wallboards and column, sectional dimensions, and the interaction among plates were investigated. • A simplified residual stress distribution model for the structural system was proposed.

Investigation of wet shot peening on microstructural evolution and tensile-tensile fatigue properties of Ti-6Al-4V alloy

Ti–6Al–4V (TC4) alloy was treated by wet shot peening (WP) using ceramic beads compared with dry shot peening (SP). The effects of shot peening on surface integrity, microstructural evolution, fatigue crack initiation behavior and tensile-tensile fatigue performance were investigated applying multiple characterization techniques. The result exhibited that the surface plastic deformation caused by WP and SP treatment resulted in microstructure changes near the surface. Surface morphology was distinctly changed by shot peening treatment. The roughness value increased from 0.596 μm (Ra) to 1.594 μm (Ra). Microhardness gradients and compressive residual stress (CRS) distributions along the depth were induced by shot peening. The maximum hardness reached 373.5 HV, 407.8 HV and 445.3 HV. The maximum value of CRS reached 884 MPa, 1038 MPa and 1207 MPa with the corresponding depth at 21 μm, 25 μm and 40 μm. The fatigue life was significantly improved by shot peening treatment. Cracks tended to initiate at the subsurface layer instead of the treated surface after shot peening. The reason for crack initiation position altering was tentatively explained by the CRS stable zone. The competition mechanism between the surface stress concentration and local strengthening factors were discussed based on the analysis of stress concentration factor, Kt.

Flexural behavior of monolith and hybrid concrete beams produced through the partial replacement of coarse aggregate with PET waste

This study was conducted to compare the structural performance of monolith and hybrid reinforced concrete beams produced by partially replacing the coarse aggregates with polyethylene terephthalate (PET) shredded wastes. The process involved casting and testing a total of 6 beams with a dimension of 3300x150x250 mm under a four-point bending moment. The control specimens were cast using normal concrete and PET monolith specimens were fabricated using PET waste concrete. Moreover, the hybrid specimens were cast using normal concrete to a depth of 150 mm from the top and PET waste concrete at the remaining 100 mm depth at the bottom. The flexural behavior of the beams was then analyzed based on the load–deflection behavior, cracking behavior, failure mode, stiffness, and ductility. The test on the hardened concrete showed that the addition of the PET waste in the mixture reduced the compressive and tensile strength of the concrete. Moreover, the hybrid specimens were also observed to have better performance than PET monolith specimens. It was also discovered that the failure mode did not change in both PET waste monolith and hybrid specimens. Furthermore, the ultimate moment capacity of the PET waste monolith and hybrid specimens was predicted using the simple analytical model for under-reinforced concrete beams and good accuracy was obtained. The findings also showed that there is a need to consider the changes in the compressive and tensile stress distribution of concrete sections for monolith PET beams in order to extend the accuracy of the analytical model.

Effect of laser shock peening on tensile properties and microstructure of selective laser melted 316L stainless steel with different build directions

316L stainless steel tensile samples were fabricated via selective laser melting (SLM), wherein the build directions (BD) deviated from the tensile directions by 0°, 45°, and 90°. The effects of BD and laser shock peening (LSP) on compressive residual stress distribution, microstructure, texture, and tensile properties were investigated. The intensity and volume fraction of strong <110> fibre texture decreased after LSP, and the sample with a build angle of 90° had the weakest intensity and the least volume fraction. A tensile test was conducted at 25 °C temperature to investigate the effects of the BD and LSP on strength and ductility. LSP resulted in a noticeable improvement in the strength of all the samples, but the ductility of the samples with 0° and 45° build angles declined. Additionally, it was found that 316L fabricated via SLM with a build angle of 90° and subjected to LSP had the optimal combination of strength and ductility.

Attainment of favorable microstructure for residual stress reduction through high-temperature heat treatment on additive manufactured inconel 718 alloy

Mitigation of residual stress in additive manufactured metal parts through post-heat treatment helps enhancement of life during service. The present work aims to investigate the effect of stress-relieving heat treatment (SRHT) at 1065 °C on microstructural changes, residual stress patterns, and mechanical properties of Inconel 718 (IN718) blocks fabricated through use of the laser-based powder bed fusion (L-PBF) process. The X-ray diffraction technique known as cos α method was used to capture the Debye ring for the measurement of surface residual stress. Dissolution of the columnar dendrites along with laves phases in the interdendritic region was seen after SRHT. The resultant microstructure showed partially recrystallized grains along with the formation of annealing twins and strengthening phases such as γ’, γ’’, and tiny metal carbides. The residual stress on the top surface of as-built sample was found to be 77% higher on the corners compared to the center region. The distribution of residual stress was seen as not uniform in the as-built condition. The SRHT sample showed uniform distribution of compressive residual stresses in all the locations. This phenomenon was due to the diffusion of atoms present in the high-stress regions migrated to low-stress regions until attaining their equilibrium. The combination of face centered cubic (FCC) and hexagonal lattices in as-built microstructure led to misfit strain between the grains. After SRHT, microstructure of IN718 experienced relaxation of residual stresses due to the transformation of hexagonal structured laves phase into the body-centered tetragonal (BCT) γ’’and FCC-structured γ’ phases. Furthermore, SRHT significantly alters the mechanical properties of IN718 alloy causing a 23.03% increase in average hardness and a 21.04% increase in tensile strength.

"Comparison of Two Types of Dual Resin Cements in Cantilever Dental Bridge Compressive Stress Distribution: Finite Element Analysis"

"Comparison of Two Types of Dual Resin Cements in Cantilever Dental Bridge Compressive Stress Distribution: Finite Element Analysis"

Theoretical study including physic-based material model to identify underlying effect of vibration amplitude on residual stress distribution of ultrasonic burnishing process

The potential of distribution of compressive residual stress at deep surface layers caused by ultrasonic-based surface sever plastic deformation (SSPD) has attracted researchers' attention to deeply study the mechanism of the process by simulation models. In majority of the researches, macro-mechanical Johnson-Cook (JC) model was utilized to govern material constitutive behavior. However, the large differences between measured and predicted values of residual stress of some materials imply that the underlying mechanism is still unclear and merits further studies. In the present work, a new physics-based constitutive equation incorporating micromechanics of initial grain size, dislocation evolution, dislocation drag and acoustic softening has been developed to obtain plastic flow stress. Then, the mechanic of the ultrasonic burnishing process incorporating superposition of static and dynamic loads was simulated using concept of expanding cavity model (ECM). The residual stress has been further calculated through combination of developed models aiming to discover the undying mechanism of vibration amplitude effect on stress fields. In order to confirm the obtained results, series of ultrasonic burnishing experiments have been carried out on AA6061-T6 under different vibration amplitude. The obtained results revealed that the developed analytical models of residual stress field are considerably more accurate than those previously established that took the macro-mechanical constitutive models to calculate plastic flow stress. Through the developed simulation model, it was studied in depth that how the vibration amplitude as the most adjustable ultrasonic vibration parameter determine variation of residual stress field. It has been demonstrated that the acoustic softening because of presence of ultrasonic energy field has the greatest impact in generation of compressive residual stress in surface and beneath layers.

Determination of muscle strength and function in plesiosaur limbs: finite element structural analyses of Cryptoclidus eurymerus humerus and femur.

BackgroundThe Plesiosauria (Sauropterygia) are secondary marine diapsids. They are the only tetrapods to have evolved hydrofoil fore- and hindflippers. Once this specialization of locomotion had evolved, it remained essentially unchanged for 135 Ma. It is still controversial whether plesiosaurs flew underwater, rowed, or used a mixture of the two modes of locomotion. The long bones of Tetrapoda are functionally loaded by torsion, bending, compression, and tension during locomotion. Superposition of load cases shows that the bones are loaded mainly by compressive stresses. Therefore, it is possible to use finite element structure analysis (FESA) as a test environment for loading hypotheses. These include muscle reconstructions and muscle lines of action (LOA) when the goal is to obtain a homogeneous compressive stress distribution and to minimize bending in the model. Myological reconstruction revealed a muscle-powered flipper twisting mechanism. The flippers of plesiosaurs were twisted along the flipper length axis by extensors and flexors that originated from the humerus and femur as well as further distal locations.MethodsTo investigate locomotion in plesiosaurs, the humerus and femur of a mounted skeleton of Cryptoclidus eurymerus (Middle Jurassic Oxford Clay Formation from Britain) were analyzed using FE methods based on the concept of optimization of loading by compression. After limb muscle reconstructions including the flipper twisting muscles, LOA were derived for all humerus and femur muscles of Cryptoclidus by stretching cords along casts of the fore- and hindflippers of the mounted skeleton. LOA and muscle attachments were added to meshed volumetric models of the humerus and femur derived from micro-CT scans. Muscle forces were approximated by stochastic iteration and the compressive stress distribution for the two load cases, “downstroke” and “upstroke”, for each bone were calculated by aiming at a homogeneous compressive stress distribution.ResultsHumeral and femoral depressors and retractors, which drive underwater flight rather than rowing, were found to exert higher muscle forces than the elevators and protractors. Furthermore, extensors and flexors exert high muscle forces compared to Cheloniidae. This confirms a convergently evolved myological mechanism of flipper twisting in plesiosaurs and complements hydrodynamic studies that showed flipper twisting is critical for efficient plesiosaur underwater flight.

STIFFNESS AND STRENGTH EVALUATION OF PRESTRESSED TIMBER BEAM WITH UNBONDED STEEL STRAND AND REINFORCED CONCRETE BEAM-COLUMN JOINT

The deformation behavior of prestressed timber beam after the gap opening occurred at the connection is evaluated in this study by the compressive stress distribution along the beam length. The correlation of moment and beam deformation is checked by three types of specimens, the results indicate that the prediction is in good agreement with the experiment results up to the proportional limit of the material. In addition, the bending ultimate strength calculated by compressive stress distribution of the interface which is set from the compressive stress-strain relationship is also verified with the value of the moment in the experiment.

Pre-collapse femoral head necrosis treated by hip abduction: a computational biomechanical analysis

Background and objectiveClinical studies indicated that femoral head collapse (FHC) occurs in 90% of patients without intervention within five years after the diagnosis of femoral head necrosis (FHN). The management of the FHN is still a great challenging task. Clinical studies indicated that hip abduction as physical therapy represents an effective hip preservation method. However, the mechanism is unclear. In this study, we use computational biomechanical technology to investigate mechanical response in FHN patients with hip abduction and establish guide protocols for FHN rehabilitation.Materials and methodsThirty computational models were constructed for evaluating the safety of hip abduction and comparing the biomechanical performance of hip abduction for the treatment of different necrotic classifications. The distribution of principal compressive stress (PCS) and load share ratio (LSR) were computed and used for biomechanical evaluation.ResultsBefore the start of physical therapy, when the size of necrotic segment is increased and located more laterally, the damage area of PCS enlarged and LSR of subchondral cortical to trabecular bone increased. As the increase of hip abduction angle, PCS of Type B transformed into Type A, PCS of Type C1 transformed into Type B, PCS of Type C2 transformed into Type C1; Except Type C2, the LSR return to normal level.Discussion and conclusionStress transfer damaged pattern correlated significantly with necrotic classification. Hip abduction motions effectively enlarge the area of PCS and recover the LSR of different structures by altering motion posture during gait. The results indicated that hip abduction may be an effective physical therapy in improving hip function and interrupt the disease pathway of FHC and THA.

Surface characteristics and stress corrosion behavior of AA 7075-T6 aluminum alloys after different shot peening processes

Shot peening is often reported as being beneficial to stress corrosion cracking resistance; however, the increased surface roughness induced by shot peening may promote localized corrosion pitting. Here, AA 7075-T6 aluminum alloys were treated by different shot peening processes, and the surface characteristic, including refined microstructure, residual stress and surface roughness, were characterized, then its effect on localized corrosion pitting and stress crack propagation behavior were investigated. Compared with single shot peening, the microstructure refinement was not further enhanced by dual shot peening with adding a subsequent low intensity of micro-shot peening. The surface residual stress distribution become more uniform, and the average surface residual stress value was increased from −158 MPa to −175 MPa. The maximum residual stress was synchronously increased from −302 MPa to −319 MPa. Meanwhile, the surface roughness (Ra) value was decreased from 4.05 μm to 2.05 μm. Compared with single shot peening, the degree of surface localized corrosion pitting was alleviated after dual shot peening due to its low surface roughness and more uniform compressive residual stress distribution. The depth of stress corrosion cracking for dual shot peening was decreased with a minimum value of 33 μm, which may be ascribed to the high maximum compressive residual stress at the subsurface.

A Numerical Simulation Method Considering Solid Phase Transformation and the Experimental Verification of Ti6Al4V Titanium Alloy Sheet Welding Processes.

A prediction model of the welding process of Ti-6Al-4V titanium alloy was established by using the finite element method, which was used to evaluate the phase composition, residual stress and deformation of the welded joints of Ti-6Al-4V sheets with different processes (including tungsten inert gas welding, TIG, and laser beam welding, LBW). The Ti-6Al-4V structures of TIG welding and LBW are widely used in marine engineering. In order to quantitatively study the effects of different welding processes (including TIG welding and LBW) on the microstructure evolution, macro residual stress and deformation of Ti6Al4V titanium alloy sheets during welding, a unified prediction model considering solid-state phase transformation was established based on the ABAQUS subroutine. In this paper, LBW and TIG welding experiments of 1.6 mm thick Ti-6Al-4V titanium alloy sheets were designed. The microstructure distribution of the welded joints observed in the experiment was consistent with the phase composition predicted by the model, and the hardness measurement experiment could also verify the phase composition and proportion. From the residual stress measured by experiment and the residual stress and deformation calculated by finite element simulation of LBW and TIG weldments, it is concluded that the effect of phase transformation on residual stress is mainly in the weld area, which has an effect on the distribution of tensile and compressive stress in the weld area. The overall deformation of the welded joint is mainly related to the welding process, and the phase transformation only affects the local volume change of the weld seam. Importantly, the phase composition and residual stress, which are scalar fields, calculated by the established model can be introduced into the numerical analysis of structural fracture failure as input influence factors.

In Silico Finite Element Modeling of Stress Distribution in Osteosynthesis after Pertrochanteric Fractures.

A stabilization method of pertrochanteric femur fractures is a contentious issue. Here, we assess the feasibility of rapid in silico 2D finite element modeling (FEM) to predict the distribution of stresses arising during the two most often used stabilization methods: gamma nail fixation (GNF) and dynamic hip screw (DHS). The modeling was based on standard pre-surgery radiographs of hip joints of 15 patients with pertrochanteric fractures of type A1, A2, and A3 according to the AO/OTA classification. The FEM showed that the stresses were similar for both GNF and DHS, with the medians ranging between 53–60 MPa and consistently lower for A1 than A3 fractures. Stresses also appeared in the fixation materials being about two-fold higher for GNF. Given similar bone stresses caused by both GNF and DHS but shorter surgery time, less extensive dissection, and faster patient mobilization, we submit that the GNF stabilization appears to be the most optimal system for pertrochanteric fractures. In silico FEM appears a viable perioperative method that helps predict the distribution of compressive stresses after osteosynthesis of pertrochanteric fractures. The promptness of modeling fits well into the rigid time framework of hip fracture surgery and may help optimize the fixation procedure for the best outcome. The study extends the use of FEM in complex orthopedic management. However, further datasets are required to firmly position the FEM in the treatment of pertrochanteric fractures.

Multi-sensor optimal deployment based efficient and synchronous data acquisition in large three-dimensional physical similarity simulation

PurposeThis paper aims to propose a deployment optimization and efficient synchronous acquisition method for compressive stress sensors used by stress distribution law research based on the genetic algorithm and numerical simulations. The authors established a new method of collecting the mining compressive stress-strain distribution data to address the problem of the number of sensors and to optimize the sensor locations in physical similarity simulations to improve the efficiency and accuracy of data collection.Design/methodology/approachFirst, numerical simulations were used to obtain the compressive stress distribution curve under specific mining conditions. Second, by comparing the mean square error between a fitted curve and simulation data for different numbers of sensors, a genetic algorithm was used to optimize the three-dimensional (3D) spatial deployment of sensors. Third, the authors designed an efficient synchronous acquisition module to allow distributed sensors to achieve synchronous and efficient acquisition of hundreds of data points through a built-in on-board database and a synchronous sampling communication structure.FindingsThe sensor deployment scheme was established through the genetic algorithm, A synchronous and selective data acquisition method was established for reduced the amount of sensor data required under synchronous acquisition and improved the system acquisition efficiency. The authors obtained a 3D compressive stress distribution when the advancement was 200 m on a large-scale 3D physical similarity simulation platform.Originality/valueThe proposed method provides a new optimization method for sensor deployment in physical similarity simulations, which improves the efficiency and accuracy of system data acquisition, providing accurate acquisition data for experimental data analysis.

Revisiting the flattened Brazilian disc configuration - Part I: The actual boundary conditions

In a recently presented analytic solution for the Flattened Brazilian Disc (FBD), it was shown that under the usually adopted assumption of uniform pressure on the flat edges of the FBD these edges turn to appear bent after deformation. Taking into account the high rigidity and flatness of the loading platens this bent sounds somehow unnatural. In the present study an attempt is undertaken to confront this unnatural bent by considering alternative non-uniform stress distributions on the flat edges of the FBD. In this context, the present paper, which is the first part of an ongoing research project, deals with the 1st fundamental problem for a FBD when it is compressed between two rigid flat stamps of the same length with the flat edge of the FBD. The distribution of the normal compressive stresses, and that of the respective frictional ones, imposed to the flat edge of the FBD are adopted from the approach of Muskhelishvili for the contact problem of a rigid flat stamp compressed against an elastic half plane, here the FBD in question. After obtaining the complex potentials for this 1st fundamental problem for the FBD, the stresses and the displacements are calculated in closed form everywhere on the FBD’s cross section. For the assessment of the analytic solution, a numerical model is also developed, with the aid of the Finite Element Method. The agreement between the theoretical and numerical analyses is satisfactory.

46 - Optimal Intrusive Force for a Periodontally Compromised Tooth: A Finite Element Analysis Strategy

The present study evaluated the optimal force for orthodontic intrusive mechanics of a tooth with different levels of periodontal support reduction using a finite element analysis (FEA) approach. An anatomical 3D model was constructed representing a second unirradicular premolar inserted into a maxillary bone segment. Based on the control model, three horizontal bone resorption conditions were simulated with alveolar bone height loss of 2 mm, 4 mm, and 6 mm (R2, R4, and R6, respectively). An 25 cN intrusive force was used for the two simulated mechanics: bilateral mini-implant intrusion and conventional intrusion. A root resorption risk index (RRRi) was calculated by dividing the maximum compressive hydrostatic stress in the periodontal ligament by the hydrostatic stress of the capillaries (4.7 kPa). It was assumed that the optimal intrusive force of reduced periodontal premolars was reached when the compressive hydrostatic stress distributions pattern of the reduced models was similar to those found in the control models of the corresponding mechanics. The FEA optimal force values for each model were compared with those obtained by the analytical formula (Force = stress x area). A linear trendline was observed between the control force reduction percentage and the bone loss height for both mechanics. For each millimeter of bone height loss, the control force had to be reduced by 9% for conventional intrusion, and by 8% for bilateral mini-implant intrusion. The root resorption risk index and the optimal intrusive force depends not only on the remaining root area with ligament support, but also on the intrusive mechanics used. The use of bilateral mini-implants in orthodontic intrusion reduced the external apical root resorption risk index and increased the optimal intrusive force. The proposed FEA strategy provided an easy, precise and feasible approach to suggest the optimum force in a clinical situation.

Modification in adsorption properties of graphene during the development of viral biosensors

The well-known effect of the local interaction between graphene and photoresist (LIGF) during the creation of biosensors is shown to lead to non-uniform distribution of compressive stresses, which deteriorates the adsorption properties of graphene, parameter reproducibility, and detecting ability of influenza B and SARS-Cov-2 biosensors. It is also shown that controlling the occurrence of LIGF areas on a graphene surface by atomic force microscopy or introducing a protective layer between graphene and photoresist can minimize the non-persistent effect of LIGF. The results of influenza B and SARS-CoV-2 imaging on the graphene surface in biosensor chips in a scanning electron microscope are presented. Keywords: graphene, biosensors, SARS-CoV-2, influenza virus B.

Изменение адсорбционных свойств графена в процессе получения биосенсоров вирусных инфекций

The well-known effect of the local interaction between graphene and photoresist (LIGF) during the creation of biosensors is shown to lead to non-uniform distribution of compressive stresses, which deteriorates the adsorption properties of graphene, parameter reproducibility, and detecting ability of influenza B and SARS-Cov-2 biosensors. It is also shown that controlling the occurrence of LIGF areas on a graphene surface by atomic force microscopy or introducing a protective layer between graphene and photoresist can minimize the non-persistent effect of LIGF. The results of influenza B and SARS-CoV-2 imaging on the graphene surface in biosensor chips in a scanning electron microscope are presented.