Maximum Design Stress Research Articles

Limitations of Gold’s formula for predicting ice thickness requirements for heavy equipment

Common practice for determining the required ice thickness for vehicles and equipment relies on Gold’s formula as outlined in provincial and territorial publications relating to ice safety. This practice persists despite recent advances in ice engineering knowledge that provide more comprehensive design methods utilizing allowable stress design approaches. The authors have identified that the use of Gold’s formula for determining required ice thickness may lead to unsafe practices when utilized in the context of heavy construction equipment, increasing the risk of ice breakthrough to personnel and equipment. The authors use recent design examples to demonstrate instances in which the use of Gold’s formula results in predicted flexural tensile stresses in the ice cover that exceed the maximum design stress recommended in contemporary literature. In the case of large excavators (53 metric tonnes) and heavy dozers (40 metric tonnes), as examples, the use of Gold’s formula for determining the required ice thickness will result in predicted flexural tensile stresses that exceed the recommended maximum design stress by 56%–71%.

Investigation of bamboo-based vertical axis wind turbine blade under static loading

Bamboo fiber composites are recyclable, low cost, high strength, and biodegradable compared to synthetic composites. Fiber-reinforced polymer composites such as glass and carbon fibers are extensively used as wind turbine blades followed by a major challenge of recycling and waste disposal etc. The present work investigates the suitability of bamboo-epoxy composite for vertical-axis wind turbine blades. The NACA 0015 and NACA 4415 blade profile has been chosen for study. The static structural analysis of blades is performed using various cross-ply and angle-ply layups. Results demonstrated that layup [45°/90°/0°/-45°]S obtained the minimum values of stress and deflection. The effect of shear webs is also analyzed. It is observed that the blade with two shear webs showed the minimum values of stress and deflection. The unidirectional strength of the composite material is also compared with the maximum design stress and found under acceptable limits. Additionally, the stress and deflection of the bamboo composite blades are compared with conventional blade materials. The stress and deflection on the non-symmetric bamboo-epoxy composite blade with double shear webs are obtained as 15.84 MPa and 4.45 mm which is observed to be decreased by 70.98% (stress) and 1.11% (deflection) respectively in comparison with glass-epoxy blade. Through the structural analysis, it is recommended that the designed blade with natural bamboo composite is acceptable for structural safety.

МЕТОД ПІДТВЕРДЖЕННЯ РЕСУРСНИХ ХАРАКТЕРИСТИК МЕТАЛЕВОЇ ЛОПАТІ НЕСУЧОГО ГВИНТА ВЕРТОЛЬОТА ЗА РЕЗУЛЬТАТАМИ ВИПРОБУВАНЬ

The helicopter main rotor blade is the basic product that determines the reliability and service life of the helicopter as a whole. The problem of predicting and ensuring the specified blade life is an urgent problem considered at the stage of its design. The analysis of the design, structural materials and design and technological solutions of the main rotor blade (RB) of the Mi-8 helicopter has been carried out. A brief description of the main rotor blade of the Mi-8 helicopter is presented. The analysis was carried out and a standard flight cycle (SFC) of the helicopter was developed. The type of bench equipment for carrying out bench fatigue tests of the blade has been selected and justified. The loads on the main rotor blade for the SFC are determined. To determine the fatigue life of a blade, it is necessary to know the characteristics of the stress-strain state. The calculation of the stress-strain state (SSS) of a blade by the finite element method (FEM) using the ANSYS system is presented. The characteristics of the stress-strain state of the spar of the regular and irregular parts of the rotor blade of a helicopter are determined using the ANSYS system. The use of numerical methods for calculating the characteristics of the stress-strain state can significantly reduce the time and cost of designing a blade. The paper presents the results of calculating the regular part of the main rotor blade of the Mi-8 helicopter in the hover mode in the case of its loading with aerodynamic and inertial load from rotation, as well as the force from its own weight. With the help of the ANSYS system, a finite element model of the regular part of the blade was developed, consisting of a set of beam elements of variable section, a calculation was carried out taking into account the geometric nonlinearity of the structure's behavior, and an analysis of the results obtained was carried out. To describe the response of materials to an external action, a model of an elastically deformable isotropic body was used with the assignment of the corresponding elastic constants of the material. The analysis of the calculation results includes the determination of reactions at the attachment points, the values of the maximum displacements of structural elements and stresses in dangerous sections. Dangerous sections are determined and the values of the longitudinal force and bending moment in these sections are calculated. The assessment of the static strength of the blade by the safety factor was carried out. When evaluating the static strength, the equivalent stresses according to Mises were considered as the maximum design stresses. To assess the fatigue strength, we analyzed the distribution of the main tensile stresses in the power elements over typical stress concentrators. The maximum level of the main tensile stresses in the dangerous section indicates that the blade material operates in the zone of high-cycle fatigue. A technique for calibrating strain gauge channels has been developed. The calculation of the characteristics of the rotor blade of a helicopter is based on the requirements set forth in the technical literature, regulatory documents. When performing work, the requirements of the Aviation Rules, Part 29 (AP - 29) were taken into account. These studies were the basis for the development of a method for confirming the resource characteristics of a helicopter main rotor blade based on the results of flight and bench tests.

Определение прочности станины конусной дробилки

The state of the direction of crushing materials in the mining industry is considered. The method of static calculation for the strength of the frame of the cone crusher KSD – 900 in two positions is given. The application of the machine at various stages of crushing is demonstrated. The comparison with other crushers of the mining industry is carried out. The design and operating principle of the digital twin of the cone crusher of medium crushing are described. The advantages and disadvantages of the machine are given. The finite element method of the CAD/CAM/CAE system NX and the module “Advanced Simulation” are considered. Today’s significance of engineering analysis is described. The calculation schemes of the cone crusher stand in several static positions are given: at the moment of lifting the stationary cone and lid, when non-crushing material enters and when the stationary cone and lid of the cone crusher are lowered. The idealization of the frame in the CAD/CAM/CAE NX system and the “Advanced Simulation” module of the cone crusher are shown to reduce the load on the calculating machine. It leads to a reduction in the calculation time of the model. Tables of external loads under the own weight of the working units of the machine are presented. The calculation of comparing the maximum design stresses with those allowed for the selected material and determining the safety factor of stand is shown.

ОБОСНОВАНИЕ КОНСТРУКТИВНЫХ РЕШЕНИЙ НЕСУЩИХ КОНСТРУКЦИЙ КУЗОВОВ ПАССАЖИРСКИХ ВАГОНОВ С ПЕРФОРИРОВАННЫМИ ПОДКРЕПЛЯЮЩИМИ ЭЛЕМЕНТАМИ

As a method of investigations there is adopted a computer mathematical modeling based on the use of a finite element method. The choice of a type and perforation parameters is connected with the problem in the large array creation of bearing structure design models of passenger car bodies. The analysis of investigations carried out in the field of multi-variation computations has shown that the most efficient investigation method is a superelement reduction. Its use allows decreasing labor and time costs for the body design model development at the expense of the initial super-element with the perforation area for a new one. 
 The appraisal of the procedure offered on the choice of a body efficient bearing structure with the perforated profiles is carried out by the example of the body of a domestic passenger car according to the criteria of strength and assurance of the highest weight reduction of a bearing structure. 
 In the first stage of the work there are defined types and parameters of perforation possible for use in the structure. Finite element design models of car bodies are developed. On the basis of strength computation results the reinforcing elements of the structure are offered which have a margin safety for perforation application in them. Based on the analysis of car body bearing structure there is carried out a choice of an efficient unit of a finite element model which will be used as a super-element. In the next stage of the work there are developed and computed structures of car bodies with the perforation types under consideration and with the use of superelements. 
 The computation results have shown that maximum design stresses of car bodies for all perforation types under consideration do not exceed legitimate values. As an efficient bearing structure of a passenger car body there is adopted a car body with the sixth type of perforation ensuring the largest decrease of structure metal intensity and satisfying strength requirements. 
 The procedure developed can be used at designing modern bearing structures of passenger car bodies having improved technical and economic values.

Precise estimation of individual leaf camber and stepping in symmetrical 65Si7 leaf springs

The term symmetrical multi-leaf spring is generally applied to springs of constant width, properly stepped leaves and each leaf of constant thickness and equal cantilever lengths. The main leaf is under the action of longitudinal and lateral forces during its operation, hence it is not desired that the maximum stress is induced in it. To reduce this stress, leaves with different unassembled cambers are assembled by pulling against each other and a common curvature is established. This causes stress concentration or set assembly stress in the assembled leaf springs. The assembly stress is subtractive from load stress in the master leaf, while it is additive to load stress in short leaves. It is possible to distribute the stress in a desirable manner among the leaves by a suitable combination of assembly stresses and stepping. The work presented in this article provides a design procedure for the number of leaves, stepping, individual leaf camber and no load assembly camber of leaf springs used in a light commercial vehicle. A proper combination of stepping and camber has been proposed by taking leaf spring design parameters into consideration, so that the stress in the leaves does not exceed maximum design stress. The leaf springs with the proposed parameters have been manufactured and tested on a full-scale leaf spring testing machine. The analytical stepping, no load assembly camber and individual leaf camber were compared with actual leaf spring for validation.

圧縮コイルばねの疲労限度線図に関する共同研究報告

In order to investigate the validity of the current JIS fatigue design diagrams for round wire helical compression springs, fatigue tests were conducted for non-shot-peened and shot-peened springs made of piano wires and valve-spring quality oil-tempered Chromium Silicon steel wires. All the spring wires supplied for the testing were commercial ones and were processed in commercial spring manufacturing lines to coil springs. Fatigue tests were conducted at room temperature until fracture or 107 cycles, under various constant stress ratios from 0.1 to 0.7. Also, load loss of each non-fractured spring at fatigue test was measured. Using each load loss thus obtained, residual shear strain γ (Shear stress relaxation divided by shear modulus) was calculated. It was found that the fatigue strengths obtained were all above the current JIS fatigue design diagrams and that the current JIS maximum design stresses were lower than those determined by the criterion that residual shear strain γ <= 0.05 % is met. Comparison of current JIS standard with the corresponding SAE and EN standards were also made.

Effect of Assembly Stresses on Fatigue Life of Symmetrical 65Si7 Leaf Springs.

The maximum stress induced plays vital role in fatigue life improvement of leaf springs. To reduce this maximum stress, leaves with different unassembled cambers are assembled by pulling against each other and a common curvature is established. This causes stress concentration or sets assembly stress in the assembled leaf springs which is subtractive from load stress in master leaf while it is additive to load stress for short leaves. By suitable combination of assembly stresses and stepping, it is possible to distribute the stress and improve the fatigue life of the leaf spring. The effect of assembly stresses on fatigue life of the leaf spring of a light commercial vehicle (LCV) has been studied. A proper combination of stepping and camber has been proposed by taking the design parameters into consideration, so that the stress in the leaves does not exceed maximum design stress. The theoretical fatigue life of the leaf springs with and without considering the assembly stresses is determined and compared with experimental life. The numbers of specimens are manufactured with proposed parameters and tested for load rate, fatigue life on a full scale leaf springs testing machine. The effect of stress range, maximum stress, and initial stress is also discussed.

Dome Window and Mount Design for a 5 MWth Solar Receiver

Large windows are being evaluated for use in high temperature concentrated solar receivers to reduce radiative and convective losses, maintain a differential pressure, and separate reactants from ambient air in receivers for chemical processing. The design of a 1.7 meter diameter fused silica dome window is evaluated for its ability to maintain acceptable stresses when exposed to pressure differentials and large heat loads from solar irradiation and re-radiation from inside the receiver. The dome must be ableto withstand the operational pressure differential of 0.5MPa where the efficiency of the solar receiver combined with a recuperated gas turbine is maximized, and glass temperatures upwards to 800°C may be observed. Brittle materials like glass need the tensile stresses to be reduced to maximize the reliability of the dome window. However, glass does not possess a characteristic strength and it is dependent on the flaw size. Careful attention to the dome mount must be taken to minimize tensile bending stresses that can cause a catastrophic or rapid failure while maintaining an environmental seal.The Weibull failure probability method is used to arrive at a projected lifetime of the window under a constant state of stress. This stress is used to determine the maximum design stresses allowed during operation of the solar receiver. Window heat fluxes from a Monte Carlo Ray Trace of the heliostat field and receiver re-radiation is utilized to couple the thermal mechanical effects of the window and its mount. A finite element analysis (FEA) is presented evaluating the stresses when considering the heat absorption in the window from transmitted light and re-radiation from within the solar receiver, combined with the applied pressure differential between the solar receiver and atmospheric conditions. The preliminary design of the window shape, thickness, and mounting strategy is presented.

Approximate optimal design of fire-resisting beams and columns

It is well known that a steel flexural beam or a compressed column designed for ordinary load conditions is rarely optimal in relation to the fire design condition. Moreover, if the addition of a protection layer is the only viable possibility in order to obtain the required fire resistance, the total cost will be probably higher than the cost of a thicker section which verifies both ordinary and fire situations. For these reasons, the beam and column shape selection problem is posed in this paper as a multicriteria optimisation task. By using an approximate solution for the stress and temperature field on a wide flange profile, and by inverting the usual stress evaluation formulas for ordinary loads, the optimal combination of geometric parameters of the steel section are obtained. If the maximum design stress is set as a fraction of the steel yielding stress, the application of the proposed method gives rise to a list of different solutions for increasing slenderness and weight; all the optimal shapes satisfy the ultimate limit state conditions for both ordinary and fire situations, and reduce considerably the design effort expended in the selection phase of an optimal shape inside the stock list. The proposed examples illustrate the effectiveness of the optimisation procedure.

Material and cooling requirements for poly-Bitter resistive magnets and hybrid inserts generating continuous fields up to 50 T

The new National High Magnetic Field Laboratory (NHMFL), equipped with a 40 MW DC power supply, will design and construct the next generation of high field resistive magnets and hybrid inserts generating DC fields up to 50 T. We present a study on the required materials and the necessary cooling characteristics, these magnets need. The configuration selected for this study consists of a combination of thin poly-Bitter and thick Bitter coils optimized in dimensions and power under constraint of maximum design stress and heat removal to obtain maximum field. The study shows that each design requires a different optimum ratio of conductor strength to electrical conductivity and that efficient cooling is only advantageous if strong copper alloys are used. For efficient use of the available power the development of new high strength, high conductivity materials will be necessary. Equally important are improvements in the heat transfer characteristics of these high power density magnets. >

Acoustic emission measurements of PWR weld material with inserted defects : Scruby, C.B.; Stacey, K.A. United Kingdom Atomic Energy Authority, Harwell, AERE-R-12386, 39 pp. (Jan. 1987)

Following an early phase of limited activity at the University of Pisa on small stainless steel pipes containing axial cracks, in 1981 ENEA, the Italian Committee for Research and Development of Nuclear Energy and Alternative Energies, has started a massive research campaign on fracture of carbon and stainless steel piping containing through and part-through cracks loaded either under pressure or in bending. The purpose of the program was to develop a better understanding on pipes fracture behaviour in order to set new design criteria more realistic, yet conservative, than the guillotine break and prepare acceptance criteria for in-service flaws particularly under the growing pressure of IGSCC that has merciless affected worldwide practically any BWR piping system.The analysis of more than 100 tests carried out at CISE research centre, in Milano, on 4 inch, 6 inch, 8 inch and 10 inch pipes has indicated that unstable fracture requires at least 150° through wall crack under ASME maximum design stresses. The leak area, before instability takes place, is always less than 10% of the net cross section area of the pipe. This has led ENEA to consider a 10% break area as a reasonable value to calculate jet forces. Further, it was found that the net section collapse load criterion by far underestimates the actual collapse load and that 360° part-through cracks tend to switch from ductile to brittle failure mode of a pipe loaded in bending.Further work is planned for the next 3 years including high temperature tests, stainless steel weldments and HAZ tests, high compliance tests and eventually burst tests. Besides the ENEA's research program, Ansaldo AMN, the Italian Nuclear Architect Engineer, is developing theoretical studies and codes to treat the problem of pipe fracture.

Outline of nuclear piping research conducted in Italy

Following an early phase of limited activity at the University of Pisa on small stainless steel pipes containing axial cracks, in 1981 ENEA, the Italian Committee for Research and Development of Nuclear Energy and Alternative Energies, has started a massive research campaign on fracture of carbon and stainless steel piping containing through and part-through cracks loaded either under pressure or in bending. The purpose of the program was to develop a better understanding on pipes fracture behaviour in order to set new design criteria more realistic, yet conservative, than the guillotine break and prepare acceptance criteria for in-service flaws particularly under the growing pressure of IGSCC that has merciless affected worldwide practically any BWR piping system. The analysis of more than 100 tests carried out at CISE research centre, in Milano, on 4 inch, 6 inch, 8 inch and 10 inch pipes has indicated that unstable fracture requires at least 150° through wall crack under ASME maximum design stresses. The leak area, before instability takes place, is always less than 10% of the net cross section area of the pipe. This has led ENEA to consider a 10% break area as a reasonable value to calculate jet forces. Further, it was found that the net section collapse load criterion by far underestimates the actual collapse load and that 360° part-through cracks tend to switch from ductile to brittle failure mode of a pipe loaded in bending. Further work is planned for the next 3 years including high temperature tests, stainless steel weldments and HAZ tests, high compliance tests and eventually burst tests. Besides the ENEA's research program, Ansaldo AMN, the Italian Nuclear Architect Engineer, is developing theoretical studies and codes to treat the problem of pipe fracture.

Response spectrum techniques for three‐component earthquake design

AbstractAn evaluation is made of response spectrum techniques as applied to seismic analysis and design of steel template offshore platforms. Such structures are designed as braced space frames for several loading conditions, including the simultaneous action of three earthquake components. Base shears as well as gross forces and combined stresses in members of three different platforms are computed for 30 real, three‐component earthquakes and response spectrum predictions, obtained by several modal‐spatial combination methods, are compared to time history solutions. Results are presented in the form of error statistics.The three approximations examined are: (a) combination of modes for one component input, (b) combination of the three partial responses to obtain estimates of total response and (c) combination of gross forces to derive maximum design stresses at a section. Attention is focused on corner piles because these are among the most heavily penalized members by three‐component excitations.It is shown that commonly used spatial combination rules may underestimate gross forces in design controlling corner members by 15–30 per cent on the average. This is attributed to correlations between motion components that create additive effects along certain directions. Typical estimates of combined stresses, however, are found to be slightly conservative.