Values Of Normal Stress Research Articles

О сброшенных напряжениях в очагах умеренных и слабых землетрясений: особенности распределения во времени

An analysis has been performed of the change in stress drops over time during the period of foreshock activity of strong earthquakes for two seismically active regions with different geodynamic settings: the Northern Tien Shan and the Southern Kuril Islands. The catalogs of earthquake dynamic parameters, DP (source ones in English publications), in these regions, with a number of events, were used as initial data. The DP catalog for the Northern Tien Shan includes 183 records of source parameters of earthquakes with magnitudes of 2.6–6.0, and the catalog for the Southern Kurils – 264 records. The stress drop values throughout a general sampling were analyzed as well as that in foreshock periods of 500 days length before the strongest earthquakes. For each region 12 such meaningful events have been specified, the magnitudes were М > 5 for the Northern Tien Shan, and М ≥ 6.5 for the Southern Kurils. The median average values of stress drops during 500-day period have been determined. The temporal variations of stress drops have been compared with changes in the b-value parameter (angular coefficient of earthquake recurrence plot) in the same observation periods. The computation of b-value for the case of the Northern Tien Shan involved the catalog data of KNET seismological network (1994–2021, more than 10 000 events), and the catalog of International Seismological Center (ISC, 1964–2000) for the Southern Kurils. In both cases, b-values were determined in 500-day moving interval with one day step. The computation gave the result that the well-known effect of b-value growth before strong earthquakes manifested itself explicitly in the considered regions. It has been established that such increase in b-value is accompanied by a decrease in the averaged stress drop values. The obtained results showed that the monitoring of the stress drop values can be used to identify the non stationary stage of the seismic regime.

Experimental study on prefabricated composite box girder bridge with corrugated steel webs

An innovative prefabricated composite box girder with corrugated steel web was proposed in this paper. This study investigated the mechanical property of the prefabricated composite box girder with corrugated steel web during two batches of tensioning of internal prestressed tendons and one field static loading test at the Jialu River Bridge in Zhengzhou, China. By analyzing the experimental, theoretical and numerical results, a finite element model was established, and the prestress transfer mechanism of the prefabricated composite box girder with corrugated steel web was revealed. The results showed that during tensioning, the prestress of the concrete floor could be effectively transferred to the concrete roof through the coordinated deformation of the web while the sheer force of the section was mainly transferred by the corrugated steel web. The concrete roof was gradually compressed, and upward deflection occurred during the tensioning. The deflection of the test beam was relatively small under the seven types of working conditions, and the deformation of the concrete roof and floor of each section satisfied the plane-section assumption. The normal stress values of the wet joint and prefabricated section of the concrete floor were consistent and changed synchronously, which demonstrates the integrality of the wet joint and prefabricated part of the beam. The test results presented in this study may provide a reference for the design and construction of such bridges.

Use of tactile sensors for horizontal stress measurements on a large calibration chamber

Large flexible calibration chambers (CCs) to evaluate and develop interpretation methods for cone penetration tests (CPTs) in cohesionless soils have been used since the late 1960s. Nevertheless, only average boundary stress values are known in almost all tests already performed. Tactile pressure sensors (TPS) represent a useful tool to assess the stress distribution in an area under loading and have been applied in some geotechnical studies. This study presents the results of CPTs carried out on a large flexible CC in a very loose and a medium-dense fine quartz sand. TPS were placed on the walls of the CC, allowing the measurement of horizontal stresses and their spatial distribution in all test phases: sample formation, lateral and cavity cell filling, piston filling, sample stressing and CPT. In particular, TPS were able to measure the horizontal stresses before the cavity and lateral cell filling – that is, when no information is available about the horizontal stresses in regular tests. The measurements contribute to the discussion on the influence of the CC boundaries on the test results. The results encourage the use of TPS on a more routine basis in large flexible CC testing.

PREDICTION OF THE BEARING CAPACITY OF THE HIP JOINT ENDOPROSTHESIS FROM THE С/C COMPOSITES

The article evaluates the bearing capacity of the hip joint endoprosthesis made of carbon/carbon (С/C) composites under anatomical load. С/C is made on the basis of carbon fiber Ural N/400-22 and phenolformaldehyde resin novolachny type RP-010. A significant complexity in modeling an endoprosthesis is the prediction of the properties of С/C. The complexity of mathematical modeling based on the mechanics of composite materials consists in the impossibility of experimentally determining the mechanical characteristics of a pyrocarbon matrix. The pyrocarbon matrix does not exist in its pure form separately from the composite material. The mechanical characteristics of the С/C are calculated, mathematical models of bone tissue and endoprosthesis are constructed, taking into account the complex composite structure. The femur is represented by a combination of cortical and spongy tissue. The femur in the study was fixed along the lateral and medial condyles of the femur. This fixation corresponds to the contact spot of the condyle with the lateral and medial menisci. The hypothesis is confirmed that the weakest component in the С/C is the pyrocarbon matrix. The position of the highest values of normal and tangential stresses are revealed. The position of concentration of tangential stresses coincide with the areas of destruction of the endoprosthesis during compression testing, which were previously visually identified. New design and technological requirements for the structure have been identified, which will contribute to increasing the reliability of the endoprosthesis.

Bio-inspired Ti‐6Al‐4V mechanical metamaterials fabricated using selective laser melting process

In the current study, porous architecture of the Euplectella aspergillum has been used to mimic mechanical metamaterial. Modelled metamaterial are fabricated using selective laser melting (SLM) process with Ti-6Al-4V alloy. The fabricated metamaterials are mechanically tested under quasi-static compressive loading condition. The heat treatment effect on compressive behavior and microstructure is also observed. The as-printed metamaterial has strength (173.36 MPa) and fracture strain (2.96%), whereas heat-treatment decreases the strength to (146.08 MPa) and increases the fracture strain to (12.60%). The increase in ductility after heat treatment is due to the formation of β-Ti and decrease in residual stresses. The presence of β-Ti phase is confirmed using microstructural and X-ray diffraction method. X-ray diffraction also confirms the decrease in tensile residual stress value from (179.5 ± 4.5 MPa) for as-printed to (96.5 ± 2.4 MPa) after heat-treatment process. Normal residual stress value is also dependent on the location of measurement on the metamaterial. However, heat treatment and location of measurement have no effect on shear residual stress. In the last, finite element simulation has been carried out to visualize the effect of diagonal struts on the deformation behavior. The result shows diagonal struts in the E. aspergillum based metamaterial helps to prevent global buckling and uniformly distribute the load, hence improves the strength of the metamaterial. • 2D Metamaterials are derived from Euplectella aspergillum • Metamaterials are fabricated using selective laser melting process with Ti-6Al-4V alloy • Mechanical and fracture behavior of the as-printed and heat-treated samples is compared • Bio-inspired metamaterial shows improved buckling resistance properties • Residual stress decreases with heat treatment and it is dependent on the topology

Determination of the stress-deformed state of a multilayer composite

An analytical determination algorithm was developed in the linear formulation, and a particular case of determining the stress-deformed state of a multilayer composite material was investigated. The algorithm is based on the use of the stress function (Ery) and the dependence of all indicators of the stress-deformed state of the material of each layer on its shape. Possible external factors affecting the composite structure are given. For the general case of building a composite structure, the sequence of adding the matrix of coefficients and the vector of free members of the system of linear algebraic equations is formed. The solution of the system of algebraic equations is proposed to be carried out by a method similar to the pre-race method, but for blocks of four equations supplemented by two equations of the influence of the previous layer in the calculation. As a result of actions similar to direct and reverse pre-race, we will obtain vectors of coefficient values of expressions of indicators of the stress-deformed state of the material of all layers as component sums.
 The acceptability of the algorithm for determining stresses and spatial deformations in a separate case of loading a composite sample with square layers is proven. The possibility of using the algorithm for the case of a significant (infinitely large) thickness the farthest from the loaded layer of the composite structure and single-layer (monolithic) material is shown. The following is established: characteristics of the distribution of normal stresses and displacements in the loaded layer of a two-layer composite material. They qualitatively coincide for different values of the Poisson coefficients of the layer materials. The amplitude of stress relief and displacements across the thickness of the loaded layer increases with a decrease in Poisson's ratio. The ratio of extreme values of normal stresses in the material of the loaded layer depends not only on the ratio of the shear moduli or the longitudinal elasticity moduli but also on the ratio of the values of the Poisson coefficients of the materials of the layers.

NF XP P94-424 standard shear test for estimating the mechanical properties of rock joints sampled from Yaounde gneisses (Cameroon)

This study is a contribution to the knowledge of rocks mechanical properties in Yaounde, with a scope on failure parameters. In most instances, this goal is achieved by carrying out XP P94-424 standard shear tests. Thus, the tests were carried out on two joint samples, using the experimental device of the Fondasol laboratory (France). However, the pairs of shear – normal stress values were plotted or computed to determine other relevant parameters. The results are expressed as graphs and value reports. (1) The global friction angle ranges around 36° for unsmoothed joints, and decreases up to 34° for smoothed joints. The friction angle ranges around 49° - 46° for unsmoothed joints, and decreases up to 3.90° for smoothed joints. The dilatancy i depend on the roughness and the type of joint surfaces; e. g. it ranged around 7° for the roughest surface while it ranged around 4° on the other. (2) At the peak the cohesion ranges around 81 kPa however, the wetness might affect this parameter up to its nullifying. At residual the cohesion ranges around 91 – 135 kPa.

Parameter Study of Interfacial Capacities for FRP-Steel Bonded Joints Based on 3D FE Modeling.

This paper investigated the stress distribution of an adhesive layer for GFRP-steel bonded joints under 22.48 kN tensile loading using a three-dimensional numerical simulation. Firstly, a stress analysis of three paths was conducted, and after comparison, path II (through the middle layer of the bonding layer) was adopted as the analyzing path. Furthermore, a systemically parametric study of the effects of the FRP stiffness (i.e., elastic modulus and thickness), bonding length, adhesive thickness, and adhesive modulus was conducted. For the joints with different FRP elastic moduli, the minimum value of normal peeling stress was calculated as -3.80 MPa by the FRP for 10 GPa, showing a significantly severe stress concentration of FRP for 10 GPa. An analysis of the von Mises stresses proved that the increase in FRP stiffness could reduce the stress concentration of the adhesive layer effectively. The study of the effect of bonding lengths indicated that a more uniform peeling stress distribution could result from the longest bonding size; the largest peeling stress of 6.54 MPa was calculated for a bonding length of 30 mm. Further parameter analysis showed that the stress concentration of the adhesive layer could be influenced by the FRP thickness, bonding thickness, and elastic modulus of the adhesive layer.

Application of Taguchi Method for Optimization of Design Parameters in Enhancement The Robust of “C” Type Snap-fits

Using statistical approaches, industrial product designs can be optimized quickly and reliably. The Taguchi method is a statistical approach that helps us to optimize the process parameters and help us to save time in terms of labor and cost. In this study, the optimization of the design parameters by using the Taguchi method for the design of the C-type snap-fit connection, which is one of the flexing fasteners used in many areas of the industry, was investigated. The design and analysis of the study was carried out by using ANSYS software. The design parameters were optimized and the effective parameters were determined. ANOVA analysis was performed to determine the effective parameters. In addition, full factorial analysis was performed to verify the method used. For example, the optimum normal stress value obtained with the Taguchi array was obtained for the combination of H1=0.4;R1=3;α1=40;α2=89;y=6 and material is PLA. When we examine the table in Figure 4, we can see that the result of 328740.27 among 729 test results and the result of the parameters in the Taguchi set match.

Objective stress values during radiation emergency medicine for future human resources: Findings from a survey of nurses.

Shortages of human resources in radiation emergency medicine (REM) caused by the anxiety and stress of due to working in REM, are a major concern. The present study aimed to quantify stress and identify which tasks involved in REM response are most stressful to help educate (human resource development) and effectively reduce stress in workers. Furthermore, the final goal was to reduce the anxiety and stress of medical personnel in the future, which will lead to sufficient human resources in the field of REM. In total, 74 nurses who attended an REM seminar were asked to answer a questionnaire (subjective) survey and wear a shirt-type electrocardiogram (objective survey). Then, informed consent was obtained from 39 patients included in the analysis. In the objective survey, average stress values of participants for each activity during the seminar were calculated based on heart rate variability (HRV). The average stress value was output as stress on a relative scale of 0-100, based on the model which is the percentile of the low-frequency/high-frequency ratio derived from HRV at any point in time obtained over time. A total of 35 (89.7%) participants answered that they had little or no knowledge of nuclear disaster and 33 (84.6%) had more than moderate anxiety. Stress values observed during the decontamination process were significantly higher than those observed when wearing and removing protective gear and during the general medical treatment process (P = 0.001, 0.004, and 0.023, respectively). Stress values did not increase during general medical treatment performed in protective clothing, but increased during the decontamination process, which is the task characteristic of REM. Stress felt by medical personnel throughout the entire REM response may be effectively reduced by providing careful education/training to reduce stress during the decontamination process. Reducing stress during REM response effectively could contribute to resolving the shortage of human resources in this field.

Discrete Fault Models

Fault surfaces are characterized by an inhomogeneous friction distribution, that can be represented with asperity models. Fault mechanics is dominated by asperities, so that a fruitful approach is to use discrete models, where asperities are the basic elements and the state of the fault is described by the average values of stress, friction and slip on each asperity. Under reasonable assumptions, the equations of motion can be solved analytically, with a deeper understanding of the behavior of the system. Fault dynamics has a sticking mode, where asperities are stationary, and a number of slipping modes, corresponding to the separate or simultaneous motion of asperities. Any seismic event is a sequence of slipping modes and a large variety of source functions is possible. Many large earthquakes are observed to be the consequence of the failure of two asperities: a discrete two-asperity model shows a rich dynamics and allows a detailed study of interaction between asperities. In this framework, fault evolution during coseismic and interseismic intervals can be calculated in terms of fault slip, stress state, energy release and seismic spectrum, including viscoelastic relaxation, fault creep and stress perturbations from other faults. Discrete models may include interaction between neighboring faults, allowing to assess conditions for the occurrence of seismic sequences in a fault system. A review of recent work on this subject is presented with applications to real earthquakes.

Effect of Axial Normal Stress and Bending Moment between Contact and Non-Contact Zone on Forming Accuracy for Flexible Stretch Bending Formation

Flexible 3D stretch bending (FSB) is a technology that uses multi-point molds instead of traditional integral molds to bend and deform profiles. Since the position of a multi-point mold can be adjusted in the horizontal and vertical directions, a set of molds can be used to form profile products with different contour structures. Due to the contact area and non-contact area between the multi-point mold and the surface of the profile, the forming accuracy of different areas is different. Thus, the axial normal stress and bending moment of the contact zone and non-contact zone between the profile and roller dies are studied in this article. By simulating the change in axial normal stress at the same position in the middle of a web along the axial direction, it is found that the axial normal stress shows little difference in the contact zone and non-contact zone. The value of axial normal stress in the non-contact zone is relatively stable, and there is a small increase on the side near the clamp. By simulating the axial normal stress of different cross-sections in the middle areas of three groups of webs, it is found that there is a linear relationship between the axial normal stress and the distance from inner curved surface. The bending moment of the profile in the contact zone is obviously greater than that in the non-contact zone, and the bending moment gradually decreases to near zero from the contact zone to the non-contact zone. The bending deformation of the profile in the contact zone is obviously greater than that in the non-contact zone, which results in the deviation between simulated bending displacement and theoretical bending displacement in the contact zone and non-contact zone.

Determination of Parameters Characteristic of Dynamic Weakening Mechanisms During Seismic Faulting in Cohesive Rocks

AbstractWhile sliding at seismic slip‐rates of ∼1 m/s, natural faults undergo an abrupt decrease of shear stress called dynamic weakening. Asperity‐scale (<<mm) processes related to flash heating and weakening and, meso‐scale (mm‐cm) processes involving shear across the bulk slip‐zone, related to frictional melting or viscous flow of minerals, have been invoked to explain pronounced velocity‐dependent weakening. Here we present a compilation of ∼100 experiments performed with two rotary shear apparatuses. Cohesive rock cylinders of basalt, gabbro, granitoid rocks and calcitic marble were sheared at various values of effective normal stress (σneff = 5–40 MPa), target slip‐rate (Vt = 0.1–6.5 m/s) and fluid pressure (Pf = 0–15 MPa). To account for the uncertainties of constitutive parameters, we introduce a norm‐based optimization procedure on a set of model parameters by comparing the shear stress evolution inferred from the proposed weakening models with the shear stress measured during the experiments. We analyze the fit to experimental data of each weakening model and we discuss a composite model in which two weakening mechanisms (namely flash heating and bulk melting, flash heating and dislocation/diffusion creep) are used to test the hypothesis that they match the shear stress evolution in different slip ranges. We found that for slip smaller than a slip‐switch distance δ0, the weakening is better described by mechanisms occurring at the asperity scale whereas for larger slip values the bulk model performs better. The inferred δ0 values decrease with normal stress suggesting that during earthquakes bulk mechanisms can govern shear stress evolution after a few centimeters of slip.

Development of Olive Harvesting Machine by Shaking

Olive harvesting machine by shaking was developed and fabricated using local materials with required specifications. The developed elements were frame and hitch, gear assembly, input and transmission shafts, vibrating unit, connecting rod, limb clamp, and transmission system. This research work aimed to evaluate the developed olive harvester capable to perform harvesting operation in the proper time using the tractor as the available economic source of power. Measurements covered the properties of olive fruit, stem, and limb for five olive varieties: Agizi, Manzanillo, Picholine, Kalamata and Arbiquen. The developed harvester was tested at three levels of frequency; 3.3, 6.7, and 10 Hz, four levels of stroke; 40, 80, 120, and 160 mm, and three levels of shaking time 60, 120 and 180 s. Results indicated that the effective range to attach the clamp on the olive limb were 30 to 40% of limb length. The average value of the maximum bending stress affecting the limb and limb deflection were 16.5 MPa and 196.6 mm respectively. In addition, results have provided the suitability of the developed shaker to harvest olive fruit. The suitability of the developed machine was judged through the fruit removal percentage. The values of performance parameters of olive harvester were 10 Hz optimum shaking frequency, 120 mm of stroke, and 120 s of shaking time.

Pembuatan dan pengujian spot welding menggunakan travo daur ulang

Spot welding is very much needed for the home industry, but the expensive welding price and large welding power make spot welding less efficient for small industries. Therefore, spot welding with small power and easy-to-carry design is needed. Spot welding design process is carried out in stages, namely planning, explaining component functions, and testing variations in the welding time used. The method used is experimental by making and testing. The specimen used is a type 304 stainless steel plate with a thickness of 0.8 mm. selected stainless steel type 304 with a thickness of 0.8 mm using a lap joint, with variations in welding time of 10, 15, and 20 seconds, using a current of 550 Ampere. The test carried out is a shear test with the AWS D8.9-97 test standard, with the aim of this study to determine the optimization of spot welding equipment using a recycled transformer on the test results. From the results of the research that has been carried out, it can be concluded that in variations of electric current and welding time, the highest average shear stress value is found at 550 A electric current by welding for 10 seconds the average shear stress is 1,060,164 (N/mm²) and the lowest average shear stress at an electric current of 550 A welding for 20 seconds the average shear stress is 564.578 (N/mm²).

Numerical modeling of injection-induced earthquakes based on fully coupled thermo-poroelastic boundary element method

In recent years, there has been a substantial increase in the induced seismicity associated with geothermal systems. However, understanding and modeling of injection-induced seismicity have still remained as a challenge. This paper presents a two-dimensional fully thermo-hydro-mechanical (THM) coupled boundary element approach to characterize the fault response to forced fluid injection and assess the effect of different injection protocols on seismic risk mitigation as well as permeability enhancement. The laboratory-derived rate-and-state friction law was used to capture the frictional paradigm observed in mature faults produced in granite rocks. All phases of stick-slip cycles, including aseismic slip, propagation of dynamic rupture, and interseismic periods, were simulated. The modeling results showed that the residual values of effective normal stress and static shear stress after a particular event completely dominate the constitutive behavior of fault friction during the next seismic event. The seismic energy analyses indicated that there is a negative correlation between the seismic magnitude and the total injected volume, such that a prolonged monotonic injection eventually results in the steady slip, rather than the seismic slip. Several fluid injection protocols were designed based on a volume-controlled (VC) approach and traffic light systems (TLS) to explore their effectiveness on the seismic risk mitigation and permeability enhancement. The results showed that cyclic injection based on TLS is the most effective approach for irreversible permeability enhancement of faults through promoting slow and steady slips. Our numerical simulations also revealed that fluid extraction (backflow-fixing bottom hole pressure at atmospheric pressure), regardless of the injection style, can considerably reduce the seismicity-related risks by preventing the fast-accelerated fracture slip during the post-injection stage. This study presents novel insights into modeling the rate-and-state governed faults exposed to forced fluid injection, and provides useful approaches for shear stimulation of faults with reduced seismic risks.

Experimental Study of Aluminium Joint Plate Between AA5052 with AA5083: Application on Hull Vessel Material

Generally, the planning of the material arrangement of the aluminum hull plate is always carried out at an early stage to obtain a material formation that has good economic value. One of the strategies used to obtain economic value in shipbuilding is the use of various grades of plate material. The grade of aluminum material that is often used on ships is the 5xxx series. Where this series has many grades that can be used as ship hull material options. The price difference for each grade of aluminum material for ships is a very influential variable on the economic value of shipbuilding. However, before being applied to shipbuilding, it is necessary to test the feasibility of aluminum plate connections with variations in plate grade. The aim is to provide clear information regarding the technical feasibility of selecting material grades. Therefore, in this study, a simulation will be carried out to test the strength of the plate connection with variations in the grade of aluminum material using the experimental method. The plate joint test is carried out using only the Tensile test in the laboratory with reference to the ASTM rules. The grades of aluminum plate materials used are 5052 and 5083. Connection formations are between 5052-5052, 5083-5083, and 5052-5083. From the test results, the largest average yield stress value is 202.34 N/mm 2 at the variation 5083-5083, the maximum average ultimate stress value is 261.70 N/mm 2 at the variation 5083-5083. For the variation of the 5052-5083 plate connection, it still has a yield stress value that is greater than the basic yield stress of the material, namely 142.97 N/mm 2 . Where the percentage value of the achievement level of yield strength is 113.6% of the basic yield stress value of the material based on BKI rules. However, in achieving the ultimate stress value, it is still lower than the ultimate basic stress of the BKI rules standard material, which is 193.88 N/mm 2 . Where the percentage value of the level of ultimate strength achievement is 70.5% of the ultimate basic stress value of the BKI rules standard material.

Impact of pulse dynamic loading direction and surface curvature on the stress-strain state of a three-layered spherical shell

On two size types of the semispherical three-layered structures, impact of the surface curvature and impact of the pulse dynamic loading on the stress-strain state (SSS) of these structures has been investigated. The layered hemispheres have been analyzed with the clamped footing and diameters (D1=0.30 m, D2=0.60 m), which had similar bearing layers’ thickness (h1=h3=0.010 m), polymeric filler with h2=0.020 m thickness, reinforced with the 5 discrete stiffening rings rigidly bound to the bearing layers.
 Values of normal stresses and vertical displacements of the structures’ bearing layers and distribution of these indicators along the spatial coordinate have been determined. Distribution of displacements’ and stresses’ magnitudes along the spatial coordinate α was determined by the software complex Nastran through the direct transient dynamic process algorithm within the time interval 0 ≤ t ≤ 10T. The time interval step duration was 0.25*10-6 s and the total number of steps was 200. The detailed and accurate calculation results have determined the choice of the solid finite element type.
 Value of the Gaussian curvature of the layered shell structures impacts their stress-strain state. Increase of the surface curvature of spherical structures under the impact of the dynamic pulse load increases the displacement and stress of their bearing layers.
 In addition to the vertical displacements and normal stresses of the bearing layers of the analyzed semispherical three-layered structures, their first natural frequency (f1) was also calculated.

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.

Prediction of the Damage Effect on Fiberglass-Reinforced Polymer Matrix Composites for Wind Turbine Blades.

The structure of wind turbine blades (WTBs) is characterized by complex geometry and materials that must resist various loading over a long period. Because of the components’ exposure to highly aggressive environmental conditions, the blade material suffers cracks, delamination, or even ruptures. The prediction of the damage effects on the mechanical behavior of WTBs, using finite element analysis, is very useful for design optimization, manufacturing processes, and for monitoring the health integrity of WTBs. This paper focuses on the sensitivity analysis of the effects of the delamination degree of fiberglass-reinforced polymer composites in the structure of wind turbine blades. Using finite element analysis, the composite was modeled as a laminated structure with five plies (0/45/90/45/0) and investigated regarding the stress states around the damaged areas. Thus, the normal and shear stresses corresponding to each element of delaminated areas were extracted from each ply of the composites. It was observed that the maximum values of normal and shear stresses occurred in relation to the orientation of the composite layer. Tensile stresses were developed along the WTB with maximum values in the upper and lower plies (Ply 1 and Ply 5), while the maximum tensile stresses were reached in the perpendicular direction (on the thickness of the composite), in the median area of the thickness, compared to the outer layers where compression stresses were obtained. Taking into account the delamination cases, there was a sinuous-type fluctuation of the shear stress distribution in relation to the thickness of the composite and the orientation of the layer.