Uniform Compressive Stress Research Articles

A novel shell-like structure Zn-5Mn alloy with high strength and high plasticity for degradable oil fracturing tools

Fracturing tools for oil and gas exploitation require high mechanical properties and degradability. Zn alloys are possible to have good mechanical properties and much lower cost than widely used rare-earth Mg alloys, so it is worthy to develop Zn alloys as alternative materials. In this paper, a novel shell-like microstructure of Zn-5Mn alloy has been realized by bottom circulating water cooling. MnZn9 phase appears by the first time in Zn-Mn alloys with Mn < 6.4 wt%. This phase leads to the formation of hard MnZn9/MnZn13 core/shell structure with a high volume fraction of 76 %, dispersed uniformly in soft Zn phase. The alloy has excellent compressive properties without fracture even when stress and strain reach 2776 MPa and 80 %, respectively. Its ultimate uniform compressive stress and strain are 865 MPa and 56 % respectively, beyond widely used dissoluble Mg alloys. Weight loss rate of the Zn-5Mn alloy is two times that of pure Zn, immersed in 3 wt% KCl solution at 93°C. The shell-like Zn-5Mn alloy provides guiding significance of applying Zn alloys in fracturing tools for oil and gas exploitation.

Effects of laser non-uniform shock peening on the microstructure and fatigue performance of SUS 304 stainless steel welded joints

Residual tensile stresses and microstructural heterogeneity in welded joints are primary factors that degrade fatigue performance. As an effective post-weld strengthening method, Laser Shock Peening (LSP) can address these issues. Given the personalized demands of different regions, this paper proposes a Laser Non-Uniform Shock Peening (LNUSP) technique. This approach involves applying high pulse energy to the weld zone (WZ) and heat-affected zone (HAZ), and low pulse energy to the base material (BM) to achieve a more uniform residual compressive stress distribution and refined microstructure, thereby improving overall performance and service life. Results indicate that LSP transforms residual tensile stresses on the weld surface into compressive stresses. Compared to original samples, uniformly LSP-treated samples, and locally LSP-treated samples, LNUSP-treated samples exhibit more uniform residual stress and hardness distribution. LSP significantly increases surface hardness, with LNUSP-treated samples achieving a maximum hardness of 308.3 HV. Additionally, LSP induces martensitic transformation in the BM and WZ areas, alters grain orientation, and promotes dislocation movement, resulting in dislocation tangling, dislocation networks, and twin structures, which refine grain size. Consequently, LSP markedly improves joint fatigue performance, delaying fatigue crack propagation. The fatigue life of LNUSP-treated samples is increased by 25.41 % compared to original samples, reaching levels comparable to high-energy large-area impacts. This enhancement is attributed to the uniform residual stress and refined grain structure.

Analysis of three-dimensional cracks horizontally placed in transversely isotropic FGMs under interior compressive stresses

This paper develops the dual boundary element method (DBEM) using a new fundamental singular solution. This new solution is the elastic fields of transversely isotropic multilayered materials of infinite extent under point concentrated loads. The discretization technique is utilized to approximate arbitrary variations of functionally graded materials (FGMs) with transverse isotropy in a graded direction. The proposed DBEM is used to analyze the three-dimensional crack problems in FGM halfspaces. The penny-shaped and elliptical cracks are horizontally placed on the interface between the FGM layer and homogeneous halfspace and are subjected to uniform compressive stresses on crack surfaces. The stress intensity factors are provided to understand the fracture behaviors of transversely isotropic FGMs. An influential factor is defined to describe the influence of the anisotropy of the FGMs on stress intensity factors. Results show that the anisotropy and heterogeneity of materials exert an obvious influence on the fracture properties of crack problems.

An Improved Radial Buckling Analysis Method and Test Investigation for Power Transformer Under Short Circuit Impact

The inner winding of the power transformer is subjected to uniform compressive stress in the radial direction during the short circuit, which makes circular radial stability a crucial component of reliability. The radial stability evaluation system currently needs more state characteristic judgment quantity considering the manufacturing deviations(MD) and assembly gaps. Thus, there is a significant deviation in the transformer design, which seriously endangers the operation safety of the power system. This paper proposes an improved radial buckling analysis method (IRBAM) to investigate the circular radial stability of inner winding. The IRBAM is implemented by defining two characteristic parameters: equivalent flexibility and MD. Besides, the relative change ratio of impedance (RCRI) is proposed as the buckling judgment for ending each short-circuit test. The destructive short-circuit tested transformer is designed with the rated power of 50 MVA and the high-voltage (HV) rated voltage of 110 kV. Then, 73 cumulative short-circuit tests are performed until impedance exceeds the permissible value based on the judgment. Finally, it is verified that IRBAM can effectively match the winding failure modes by comparing the buckling phenomena and calculation results. Further, the IRBAM can provide a reference for similar designs and verification with more minor deviations.

Interfacial delamination for an orthotropic thin film/substrate system

In this study, the interface behavior of an orthotropic thin film bonded imperfectly to an orthotropic substrate is considered. The analytical method employs the integro-differential formulation with the aid of membrane assumption. The loading scenarios include either a constant temperature rise applied to the film or a uniform compressive stress applied to the film edges. The sensitivity of the film stresses as well as the shear stress singularity factor to the different material combination are extracted. The results indicate that the shear stress singularity factor dramatically increases as the delamination length exceeds 50% of the film length. The results of this study would be useful for the design engineers focused in flexible and stretchable electronic devices

A flexible bearing plate based on steel plate and rubber mat

The bearing plates used in plate load test for highway engineering are typically rigid. However, due to limitations in obtaining the accurate distribution of compressive stress at the bottom of the bearing plate, there is often a significant deviation between the measured subgrade resilient modulus and the actual condition. To address this issue, a flexible bearing plate can be used to test the subgrade and obtain a more accurate resilient modulus. In this study, we use variance and degree of mean deviation to quantitatively evaluate the distribution uniformity of compressive stress. To create a rigid-flexible bearing plate that is similar to a flexible bearing plate, we explore the combinatorial design of steel plates and rubber mats. We examine factors such as the thickness (10, 20, and 30 mm) of the steel plate, elastic modulus (5, 10, and 20 MPa) and thickness (10, 20, and 30 mm) of the rubber mat, friction coefficient (μ:0, 0,2, 0.4, 0.6, 0.8, ∞) between the bearing plate and subgrade, and the combined shape characteristics of the rubber mat and steel plate. To reduce friction between the rubber mat and subgrade, we use lubricant, and through our design process, we develop a flexible bearing plate with relatively uniform compressive stress. Our computations show that when μ = 0.05, the variance is 0.0001, and the degree of mean deviation is 0.0780. These results indicate that the distribution uniformity of the compressive stress is very close to the uniform distribution load, which meets the necessary accuracy requirements for engineering applications.

Study on the Residual Stress Distribution of Bi-Directional Cold Expansion Process Performed on Open Holes

AbstractTraditional unidirectional cold expansion technology usually generates non-uniform distribution of residual stress in the thickness direction of holes, which is harmful to the improvement of fatigue life of holes. The present work proposed a bi-directional cold expansion procedure to realize the homogenization of residual stress in the thickness direction of the cold expanded hole, thereby further improved antifatigue performance of cold expanded hole. For this aim, a series of finite element (FE) simulations were carried out to investigate the effectiveness of the bi-directional cold expansion procedure and optimize the process parameters. The results showed that the optimized bi-directional cold expansion process generated a more uniform distribution of residual circumferential compressive stress in the thickness direction comparing to the simplified bidirectional cold expansion process using a single mandrel. For the Aluminum alloy 7050-T7451, when the first interference level I1 = 1.8%, the largest and the most uniform residual circumferential compressive stress was achieved, which suggested the best anti-fatigue performance.

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.

Core-shell heterostructure-enabled stress engineering in vanadium dioxide nanobeams

In strongly correlated materials (SCMs), especially for vanadium dioxide (VO2), manipulating physical properties through stress engineering is an important issue for the use of ultrafast metal-insulator transition (MIT) in device applications. Recent research efforts have mainly focused on modulation and related phenomena of physical properties by epitaxial and mechanical stresses in VO2 films or anisotropic nanocrystals. However, inhomogeneous stress in such planar and nanocrystal systems leads to complications induced by phase competitions or the creation of intermediate phases. Here, we demonstrate the core-shell heterostructures-enabled stress engineering on MIT, which provides accommodation of uniform axial stress and control of phase transition pathways in VO2 nanobeams. Specifically, the VO2 nanobeams with an amorphous Al2O3 shell undergo a simple and direct MIT at lower temperatures without intermediate phases, distinctly different from pristine nanobeams with coexisting phases. For the core-shell nanobeams, the VO2 core sustains a uniform compressive stress state along the nanobeam length caused by shell formation, which can be attributed to the different thermal behaviors coupled to the elastic modulus between the VO2 and shell. Our results can lead to better engineering of phase transitions in SCMs, providing the beneficial effect of suppressing inhomogeneities during the MIT process.

New Design Proposal for Stiffened Curved Plates under Compression

AbstractIn this paper, the stability behaviour of longitudinally stiffened, transversally curved steel plates under uniform compressive stresses is investigated and new design guidelines are proposed to extend the scope of the current European standards for flat plated structures to stiffened curved plates. For this purpose, a numerical model is built in Abaqus, which is verified with own test results and numerical results from the literature. It incorporates geometric imperfections based on the modification of node coordinates using sinusoidal functions, and is further used in a comprehensive parametric study based on nonlinear numerical analysis (GMNIA). The parametric study investigates the effects of curvature, slenderness of the plate, size of stiffeners and shape of initial imperfections on the ultimate resistance of the stiffened curved plates. From the results, some important conclusions are drawn regarding the structural behaviour and the positive effects of curvature on the cross‐sectional resistance. In particular, it is found that stiffened curved plates are less sensitive to the shape of the initial imperfections compared to flat stiffened plates, and the introduction of curvature generally adds a reserve of resistance to the stiffened panel under compressive stresses. Based on numerical results, design rules are proposed for longitudinally stiffened curved plates subjected to compressive stresses. The rules are in accordance with the formalism of EN 1993‐1‐5 for flat plated structures and follow the effective width concept. The maximum loads obtained from numerical analysis are compared with the new design rules and a good correlation is obtained.

Incomplete contact between a coated elastic substrate and rigid foundation perturbed by a rigid disc

This paper investigates an axisymmetric and frictionless contact problem of a coated elastic substrate pressed onto a rigid foundation with a rigid disc by remoted uniform compressive stress. Such an incomplete contact problem is formulated as a three-parts mixed boundary values problem (MBVP). By means of Hankel transform technique and a new solution derived for a multilayered elastic solid subjected to surface displacement (dislocation), the MBVP is converted to a system of triple integral equations. A series expansion method characterized by expressing the unknown surface displacement as Bessel function series is adopted to solve the triple integral equations. Explicit analytical expressions for contact stress, resultant contact force and Mode-I stress intensity factor are obtained. The accuracy of the present solutions is verified by comparing to the results available in the literatures for the simple cases of a single layer and a homogeneous half space. Numerical studies are also performed to investigate the contact mechanics of coated material under incomplete contact. Results from this study are valuable for the design of coating to protect engineering machine components against third-body abrasive particles or solid contaminants induced contact damage.

Humerus osteology, myology, and finite element structure analysis of Cheloniidae.

Adaptation of osteology and myology lead to the formation of hydrofoil foreflippers in Cheloniidae (all recent sea turtles except Dermochelys coriacea) which are used mainly for underwater flight. Recent research shows the biomechanical advantages of a complex system of agonistic and antagonistic tension chords that reduce bending stress in bones. Finite element structure analysis (FESA) of a cheloniid humerus is used to provide a better understanding of morphology and microanatomy and to link these with the main flipper function, underwater flight. Dissection of a Caretta caretta gave insights into lines of action, that is, the course that a muscle takes between its origin and insertion, of foreflipper musculature. Lines of action were determined by spanning physical threads on a skeleton of Chelonia mydas. The right humerus of this skeleton was micro-CT scanned. Based on the scans, a finite element (FE) model was built and muscle force vectors were entered. Muscle forces were iteratively approximated until a uniform compressive stress distribution was attained. Two load cases, downstroke and upstroke, were computed. We found that muscle wrappings (m. coracobrachialis magnus and brevis, several extensors, humeral head of m. triceps) are crucial in addition to axial loading to obtain homogenous compressive loading in all bone cross-sections. Detailed knowledge on muscle disposition leads to compressive stress distribution in the FE model which corresponds with the bone microstructure. The FE analysis of the cheloniid humerus shows that bone may be loaded mainly by compression if the bending moments are minimized.

Strengthening mechanism of Nd: Yag laser shock peening for commercially pure titanium (CP-TI) on surface integrity and residual stresses

Abstract In the present work, an attempt has been made to investigate the effect of generating shock waves through direct and confined ablation modes of plasma method of massive laser shock peening (MLSP) on surface integrity of cast dumbbell shaped and cylindrical cast specimens of commercially pure titanium (CP-Ti) and to compare with those of untreated CP-Ti. The MLSP is usually performed in a massively peening mode to induce uniform compressive residual stress and surface deformation across the entire specimens. After MLSP, tensile testing was carried out to obtain the tensile strength, modulus of elasticity and percentage elongation. The microstructural and surface topography investigations of the laser shock peened material were carried out using digital, optical microscopy and SEM equipped with an energy dispersive spectrometer (EDS) and XRD. The results show that laser shock peened with confined ablation make the surface of CP-Ti with improved change in microstructure, increase in tensile strength, microhardness (73.08%), surface roughness and compressive residual stresses (−420 MPa) which prolongs the mastication ability and dimensional stability of dental implant restorative materials.

Counterion Exchange in Peptide-Complexed Core-Shell Microgels.

The complexation of polyvalent macroions with oppositely charged polyelectrolyte microgels can lead to core-shell structures. The shell is believed to be highly deswollen with a high concentration of counter-macroions. The core is believed to be relatively free of macroions but under a uniform compressive stress due to the deswollen shell. We use cryo-scanning electron microscopy (SEM) with X-ray microanalysis to confirm this understanding. We study poly(acrylic acid) (PAA) microgels which form a core-shell structure when complexed with a small cationic antimicrobial peptide (L5). We follow the spatial distribution of polymer, water, Na counterions, and peptide based on the characteristic X-ray intensities of C, O, Na, and N, respectively. Frozen-hydrated microgel suspensions include buffers of known composition from which calibration curves can be generated and used to quantify both the microgel water and sodium concentrations, the latter with a minimum quantifiable concentration less than 0.048 M. We find that as-synthesized PAA microgels are enriched in Na relative to the surrounding buffer as anticipated from established ideas of counterion shielding of electrostatic charge. The shell in L5-complexed microgels is depleted in Na and enriched in peptide and contains relatively little water. Our measurements furthermore show that shell/core interface is diffuse over a length scale of a few micrometers. Within the limits of detection, the core Na concentration is the same as that in as-synthesized microgels, and the core is free of peptide. The core has a slightly lower water concentration than as-synthesized controls, consistent with the hypothesis that the core is under compression from the shell.

Stability of stiffened cruciform steel columns under shear and compression by the complex finite strip method

This paper focuses on the stability of steel columns with cruciform section under uniform compressive and shear stresses. The complex finite strip method (CFSM) is employed to solve the buckling of open thin-walled steel columns. CFSM results are validated against other numerical techniques. CFSM has high convergence, accuracy and superior computational efficiency. Due to the use of complex functions, it can also capture shear buckling. The influence of longitudinal stiffeners and section geometry on the buckling behavior of stiffened cruciform sections is investigated. The buckling behavior of cruciform sections is compared against U, I, and T section steel columns.

Texture and microstructure improvement of hot-deformed magnets with platelet-like nano h-BN addition

The microstructure of ribbons interface was optimized by doping the hexagonal boron nitride nanoplatelets (h-BNNP) in hot-deformed magnets. The remanence increased markedly and reached to a maximum value of 14.06 kGs. The coercivity and the energy product exhibited similar variation trends to the remanence, showing maxima of 16.92 kOe and 49 MGOe, respectively. Microscopy observations revealed that surface grains of ribbons tended to align with the interior grains due to the uniform local compressive stress induced by h-BNNP with relatively large flat surface, resulting in hot-deformed magnets with microscopically homogeneous structure and improved texture.

Flange local buckling of pultruded GFRP box beams

An experimental program investigating the flange local buckling (FLB) behavior of pGFRP box-sections is reported. The commonly accepted design equation based on plate theory was validated although importance of accurate assessment of the rotational stiffness of the web-flange junctions was identified. It is concluded that the lower bound solution, assuming the flange is a simply-supported plate subject to uniform compressive stress, results in uniformly conservative predictions of the critical FLB moments. The theoretical solution accounting for flange plate edge support stiffness based only on web stiffness, material and geometric properties of the cross section over predicts the support stiffness resulting in unconservative predictions of FLB behavior. The rotational stiffness of flange-web junction of the pGFRP box-section is also investigated experimentally. It is found that the actual rotational stiffness of flange-web junction is relatively low, closer to the simply-supported boundary condition. The role of fiber architecture at the web-flange junction is identified as affecting this behavior. The conclusions of this study support the use of the lower bound solution for design of pGFRP box-sections.

Development and Use of a Small Laboratory Intensive Quenching (IQ) System

Abstract Intensive quenching (IQ) has been defined as “those quenching conditions that lead to uniform maximum surface compressive stresses,” which provide maximum surface compressive stresses with correspondingly optimized distortion control. An earlier paper described the design and construction of a laboratory system that provides sufficient heat transfer rates to be classified as an IQ system. This paper describes the experimental work conducted with this laboratory IQ system. Particular focus will be on construction and use of this laboratory device to quench SAE 5160 spring steel under IQ conditions and the corresponding cooling curves, heat transfer rates, and compressive stresses obtained.

Measurement of microscale residual stresses in multi-phase ceramic composites using Raman spectroscopy

A methodology is described for characterizing the spatial distribution of thermal mismatch stresses at grain level in B4C-SiC-Si ceramic composites using Raman spectroscopy. Unlike traditional methods to detect residual stresses (e.g., X-ray diffraction) which provide average values of stress over the entire specimen surface, Raman peak-shift analysis provides residual stress distributions within the microstructure at high spatial resolution. While classical formulation predicts uniform compressive stress within a Si-phase surrounded by the ceramic matrix, the Raman measurements revealed non-uniform residual stress distributions in Si when the particle size was larger than 5 microns. For large irregular shaped particles, the two methods coincide only along the interface between the particle and matrix, but vary drastically both in magnitude and nature in the interior of the particle where large tensile stresses have been measured. The presence of anomalous tensile stress in the interior of the minor Si-phase results in defect generation and structural disorder which has been confirmed by TEM analysis. Raman spectroscopic mapping was also used to compute an average macroscale residual stress value for a given material composition allowing links to be drawn between processing, microstructure and properties. The average residual stress within the microstructure was found to correlate well with the estimates based on volume fraction of the constituents and material properties.

THE LATTICE PARAMETERS AND RESIDUAL STRESSES IN BULK NANOCRYSTALLINE AND ULTRAFINE-GRAINED TITANIUM

Lattice parameters and residual stresses in the bulk nanocrystalline/ultrafine-grained titanium were studied by X-ray diffraction methods. The investigated samples were prepared using the method of the cryomechanical grain structure fragmentation with multiple rolling at the temperature of liquid nitrogen to the true strain value |e| = 3. Phasic change of the a and c parameters has been found with increasing degree of cryoreduction. This change was stronger for the parameter a. The observed change parameters associated with a relative slip and twinning activity (initial cryo-reduction stage) as well as the formation of the nanocrystalline state (at higher degree of deformation). The most likely source of residual stresses arising in titanium at cryorolling is heterogeneous plastic deformation. The production of nanocrystalline / ultrafine-grained titanium using cryomechanical grain fragmentation method is accompanied by the formation of uniform compressive residual stresses in the informative deformable layer of billet.