Experimental Stress Analysis Research Articles

Degradation mechanism for mechanical property of carbon fiber reinforced epoxy composite under simulated seawater absorption coupled with flexural load

Property evolution of carbon fiber reinforced epoxy composite used in marine environment was investigated in this paper. The moisture absorption and flexural properties of carbon fiber composite laminate were studied under the combined pretreatment condition of simulated seawater and three-point flexural load. An in-situ observation system was used during mechanical test to analyze damage initialization and development on dry and wet composites. Theoretical analysis considering hydro-mechanical coupling was conducted, based on experimental data, moisture simulation and stress analysis. Stress distribution under flexural load was discussed using finite element method, and its effects on moisture diffusion and failure process were analyzed based on the theoretical and experimental results. It demonstrates that moisture absorption of composites is inhibited as flexural load is applied during moisture absorption. It is attributed to compressive stress concentration of composite on the loading region. The retention of flexural property shows slight increase under moisture coupled with flexural load, which is resulted from decreased moisture content. Failure process of composite during three-point flexural test after immersion is different from that of dry composite, especially for the position and number of crack formation and propagation. Weakened interlaminar interface and more large cracks are found after immersion coupled with flexural load, which are explained based on water degradation and initial damage at stress concentration region. It denotes that more attentions should be paid on failure process of wet composite structure in marine field.

Numerical and experimental residual stress analysis of dissimilar metals of Inconel 718 and AISI 316 developed in GTAW process

Numerical and experimental residual stress analysis of dissimilar metals of Inconel 718 and AISI 316 developed in GTAW process

Experimental Stress Analysis of Spherical Roller Bearing for High-Speed Trains Using Photoelasticity

Experimental Stress Analysis of Spherical Roller Bearing for High-Speed Trains Using Photoelasticity

Experimental Analysis of Residual Stresses in CFRPs through Hole-Drilling Method: The Role of Stacking Sequence, Thickness, and Defects

Carbon fiber reinforced plastics (CFRPs) gained high interest in industrial applications because of their excellent strength and low specific weight. The stacking sequence of the unidirectional plies forming a CFRP laminate, and their thicknesses, primarily determine the mechanical performance. However, during manufacturing, defects, e.g., pores and residual stresses, are induced, both affecting the mechanical properties. The objective of the present work is to accurately measure residual stresses in CFRPs as well as to investigate the effects of stacking sequence, overall laminate thickness, and the presence of pores on the residual stress state. Residual stresses were measured through the incremental hole-drilling method (HDM). Adequate procedures have been applied to evaluate the residual stresses for orthotropic materials, including calculating the calibration coefficients through finite element analysis (FEA) based on stacking sequence, laminate thickness and mechanical properties. Using optical microscopy (OM) and computed tomography (CT), profound insights into the cross-sectional and three-dimensional microstructure, e.g., location and shape of process-induced pores, were obtained. This microstructural information allowed for a comprehensive understanding of the experimentally determined strain and stress results, particularly at the transition zone between the individual plies. The effect of pores on residual stresses was investigated by considering pores to calculate the calibration coefficients at a depth of 0.06 mm to 0.12 mm in the model and utilizing these results for residual stress evaluation. A maximum difference of 46% in stress between defect-free and porous material sample conditions was observed at a hole depth of 0.65 mm. The significance of employing correctly calculated coefficients for the residual stress evaluation is highlighted by mechanical validation tests.

Experimental Stress Analysis and Stress Concentration Factor – A Review

A machine component goes through various stress conditions and it is essential for a designer to analyze the stresses generated in the component accurately. Experimental stress analysis plays a vital role in designing a component.

Stress concentration effect on deflection and stress fields of a master leaf spring through domain decomposition and geometry updation technique

Abstract Theoretical and experimental large deflection and stress analysis of a master leaf spring considering stress concentration effect of clamping is reported. The non-uniformly curved master leaf spring under three point bending subjected to moving boundaries is modeled. Geometrically nonlinear strain-displacement relations, as necessary for the theoretical analysis, are derived through visualization of physics behind the large deformation problem. An embedded curvilinear coordinate system is considered, to study the combined effects of non-uniform curvature, bending, stretching and shear deformation including cross-sectional warping. Governing equation of the non-uniformly curved beam system is derived in variational form using energy method, based on linear material constitutive relations and the derived nonlinear kinematic relations. An iterative solution scheme through successive geometry updation is developed and executed in MATLAB® software to solve the governing equation involving strong geometric nonlinearity together with complicating moving boundary effect. Experimental deflection profiles under static loading are obtained through manual image processing technique using AutoCAD® software. Whereas, strain measurements are performed using strain gauges with data acquisition system (HBM-MX840B). Comparison between the theoretical and experimental results lead towards observation on stress concentration effect due to presence of geometric discontinuity in form of a small hole in the physical system. A modified formulation is proposed using domain decomposition method incorporating effect of geometric discontinuity through an equivalent curved beam geometry of variable cross-section. The modified theoretical model is validated successfully with the experimental results, and observations on stress characteristics and effect of hole diameter to beam width ratio are made.

55 Years of Holographic Non-Destructive Testing and Experimental Stress Analysis: Is there still Progress to be expected?

Holographic methods for non-destructive testing, shape measurement, and experimental stress analysis have shown to be versatile tools for the solution of many inspection problems. Their main advantages are the non-contact nature, the non-destructive and areal working principle, the fast response, high sensitivity, resolution and precision. In contrast to conventional optical techniques such as classical interferometry, the holographic principle of wavefront storage and reconstruction makes it possible to investigate objects with rough surfaces. Consequently, the response of various classes of products on operational or artificial load can be examined very elegantly. The paper looks back to the history of holographic metrology, honors the inventors of the main principles, discusses criteria for the selection of a proper inspection method, and shows exemplary applications. However, the main focus is on modern developments that are inspired by the rapid technological process in sensing technology and digitization, on current applications and future challenges.

Mechanical characterization of adhesive layer using Double strap joint specimens

In practical applications, most of our mechanical and civil structures are subjected to either oscillatory or static load. To design those structures, stress analysis is needed to withstand the design loads. In experimental stress analysis, strain gauges are mounted on those structures to determine stress at a point. Usually, strain gauges are mounted on the substrate using proper adhesives. The quality of strain data is a function of proper mounting. The thickness of adhesives used for mounting techniques should be optimum and very thin to ensure quality results. The underlying adhesive layer acts as an interface between the substrate and the strain gauge. This adhesive layer receives the maximum shear stress when the member is loaded in tension. Therefore, in this research work, the main focus is on characterizing the Araldite adhesive material. A tension test was conducted on the prepared bulk specimen to characterize the adhesive. The Double Strap Joint (DSJ) tests were conducted to investigate the interfacial shear strength and failure modes according to ASTM D 3528 standards. Two sets of specimens, such as plain and knurled straps, were used in this research work. The failure mode in the plain strap joint shows cohesive failure, and the knurled strap joint shows adhesive failure.

Experimental and numerical stress and strain analysis of the boiler reversing chamber tube plate

Boilers are one of the most used units for both heat generation plants and industry systems. Their operation is subjected to different working loads and maintenance requirements. Exploitation experience points out critical boiler zones where failures and break downs typically occur. This paper analyzes critical zones in hot water fire-tube boiler. Experimental procedure was performed on the model of this type of boilers and its critical element. The tube plate of hot water boiler was identified as the most critical one. Experimental analysis and numerical model verification were performed using Aramis system based on 3-D digital image correlation method. Numerical analysis was done in ANSYS software package and verification of results was done based on measurements obtained by strain gauges and local measurements performed by the Aramis system. Stress-strain analysis indicates the critical zones of boiler tube plate. The character of change parameters such as strain and stress occurring in the critical zones can be verified both by experimental and numerical data. The paper presents a novel approach in experimental and numerical analyses that can be conducted in similar units and used for existing unit optimization, as well as for new product testing on different loads and provide opportunity for further development and improvement for practical industrial application.

Strength calculations and fatigue tests of welded bus bodywork nodes

Laboratory fatigue life tests were performed for several structural variants of welded nodes of thin-walled profiles of a bus bodywork. The laboratory fatigue tests were supported by FEM calculation and strain gauge experimental stress analysis. S-N curves were evaluated and used to predict the fatigue life of these structural nodes under random operational loading of the vehicle bodywork. Measuring systems for on-line monitoring of stresses in the vehicle bodywork have been developed and applied.

Effect of speckle size on surface crack detection via digital image correlation

Digital image correlation (DIC) is an experimental stress analysis technique used in nondestructive tests. The accuracy of DIC in crack detection depends on various factors such as the sizes of speckles and pixels. In the current study, a speckle pattern based on the spreading of nanoparticles with small speckles is compared with a conventional sprayed pattern to understand whether crack detection via DIC is improved by reducing the sizes of speckles and pixels. Owing to the small size of nanoparticles, an optical microscope is used for magnification. The spreading method for crack detection is first investigated experimentally. Results show that cracks can be detected easily when a 250 nm opening appears in the crack edges. Subsequently, the spreading method is compared with the conventional DIC, in which the spraying method is used for patterning, in terms of crack detection. Results show that by reducing the speckle size and closely analyzing the speckle pattern, the DIC technique is considerably better than the conventional technique in detecting small cracks. Moreover, the conventional method is more suitable for detecting large cracks.

Research on electrical strain gages and experimental stress analysis: Case study for a full wheatstone bridge

This study investigated electrical strain gage technology, which is widely used in experimental stress measurement, on an application. Strain gages are used to precisely measure strain directly in a system. This method is carried out to verify the numerical and analytical calculations performed or to record the strain data generated during the active duty of a system and to investigate the fatigue damage. In particular, verifying numerical calculations in the strength-material recovery optimizations of mass-produced systems contributes to the development of the system. In this study, strain measurement using strain gage and strain measurement technology is presented on an application. Information was given about strain gages. A full bridge wheatstone bridge consisting of 4 linear gages was created on a prototype. The system was tested with a load cell validation. Structural finite element analysis of the prototype and analytical calculation of the fullbridge strain gage connection were performed. The results showed that the measurement with the strain gauge differed 1.20% and 1.40% from the analytical and numerical results, respectively. Thus, precision strain measurement technology was successfully presented in engineering systems.

Theoretical and Experimental Analysis of Inter-Layer Stresses in Filament-Wound Cylindrical Composite Structures.

This paper analyses the issues relative to the modelling of tubular (cylindrical) composite structures. This paper aims to describe the design of a multi-layer structure of filament-wound composite pipes where, after loading, the hoop-stress distribution would be as uniform as possible. That would allow the mass of the composite to decrease while maintaining the proper mechanical strength. This publication presents the development of a calculation model dedicated to mono- and multi-layered tubular composite structures. The equations describing the stress pattern were based on the Lamé Problem, whereas to describe the modelled structures, an anisotropy coefficient was introduced and interlayer pressures values were determined. To verify the calculations, experimental studies were performed. The test specimens were fabricated by winding fibre bundles around a steel core (as rings with an internal diameter of 113 mm and a height of 30 mm). For the test, the method of pressing a conical ring into a split ring, which acts on the internal surface of the tested cylindrical sample, was selected. The operation of the test rig (test stand) was simulated using the Finite Element Method (FEM). Measurements with strain gauges were conducted during the experiments.

Finite Element and Experimental Analysis of Residual Stresses in Electron Beam Welded Nickel-Based Superalloys

In this paper, two different nickel-based superalloys, namely Inconel 718 and Nimonic 80A were joined using electron beam welding techniques with three different welding parameters. A finite element analysis (FEA) using Abaqus software was carried out to calculate the residual stresses due to welding. Both transverse and longitudinal residual stresses were determined. Also, an X-ray residual stress measurement system, μ-X360 Ver. 2.5.6.2 was used for measuring transverse residual stress along and across the weld centerline. The transverse residual stress found by FEA and that measured experimentally was nearly the same thus validating the FEA. Also, the peak values of longitudinal residual stress found using the FEA were close to the yield strengths of the base metals as found elsewhere.

3D FE modeling and experimental analysis of residual stresses and machining characteristics induced by dry, MQL, and wet turning of AA6061-T6

The present research study aimed to investigate the influences of turning environments and parameters on machining temperature (MT), machining forces (MFs), and axial surface residual stresses (ASRS) in turning operation of AA6061-T6. Turning environments included DRY, minimum quantity lubrication (MQL), and WET modes, and turning parameters consisted of cutting speed (), feed rate (), depth of cut (), tool nose radius (), side cutting edge angle (SCEA), and back rake angle (BRA). A 3D finite element (FE) model was developed to predict MT, MFs, and ASRS for different turning environments and parameters and was validated by experimental measurements. The results showed that increasing feed rate led to a higher tensile ASRS while using tools with a nose radius of 0.4 resulted in lower ASRS. In addition, the deviation of SCEA from 0° to positive or negative values caused higher tensile ASRS. ASRS increased with decreasing BRA from 0° to –15°. The variation of ASRS was found to be more sensitive to thermal effects than to mechanical ones. The results further confirmed that in a turning process, the competition between the machining forces and temperature was the fundamental factor that determined the extent of residual stresses.

Experimental analysis of mechanical behaviour and residual stresses of EN-36C alloy steel with and without tempering

The intense demands of nickel chromium case hardened steel (EN-36C) alloy steel in different engineering applications are increasing day by day due to its cheap and easy availability. The effect of different stages of tempering on EN-36C alloy steel has been carried out to check the mechanical behavioural, microstructural properties and residual stresses in the present work. The effect of tempering on response variables viz., material removal rate, surface roughness, tool tip temperature and residual stresses are evaluated. The cosα method is used to measure the residual stresses in the specimen using two-dimensional detectors such as imaging plates. Further, the influence of tempering on mechanical properties such as tensile strength, hardness, toughness and percentage elongation has been observed. Experimental results depicted that the ductility and toughness are improved without significant change in hardness in the specimen tempered at 500°C. The mechanical properties of specimens tempered at 500°C are found to be a tensile strength of 680.42 MPa, hardness 92 Rockwell hardness of scale B and toughness 187 J. The maximum value of material removal rate (12596.80 mm3/min), minimum tool tip temperature (61.33°C), average surface roughness ( Ra = 1.93, Rq = 2.36, Rz = 10.30) and lowest residual stress 217 MPa are observed in the specimens tempered at 500°C.

Experimental Analysis and Prediction Model of Milling-Induced Residual Stress of Aeronautical Aluminum Alloys

Aeronautical thin-walled frame workpieces are usually obtained by milling aluminum alloy plates. The residual stress within the workpiece has a significant influence on the deformation due to the relatively low rigidity of the workpiece. To accurately predict the milling-induced residual stress, this paper describes an orthogonal experiment for milling 7075 aluminum alloy plates. The milling-induced residual stress at different surface depths of the workpiece, without initial stress, is obtained. The influence of the milling parameters on the residual stress is revealed. The parameters include milling speed, feed per tooth, milling width, and cutting depth. The experimental results show that the residual stress depth in the workpiece surface is within 0.12 mm, and the residual stress depth of the end milling is slightly greater than that of the side milling. The calculation models of residual stress and milling parameters for two milling methods are formulated based on regression analysis, and the sensitivity coefficients of parameters to residual stress are calculated. The residual stress prediction model for milling 7075 aluminum alloy plates is proposed based on a back-propagation neural network and genetic algorithm. The findings suggest that the proposed model has a high accuracy, and the prediction error is between 0–14 MPa. It provides basic data for machining deformation prediction of aluminum alloy thin-walled workpieces, which has significant application potential.

Investigating the effects of post-heat treatment on residual stress in AlSi12 parts processed with Selective Laser Melting

Residual stresses are the stresses that remain on a part after the original cause of any stress has been removed. In Selective Laser Melting (SLM), an additive manufacturing process, residual stress occurs in the created part due to rapid melting and rapid solidification; these stresses are responsible for distortion, which must therefore be minimised or eliminated. Residual stresses can be reduced in SLM built parts by the application of post heat treatment, and this process is investigated in this study. X-ray diffraction was employed for the experimental analysis of the residual stresses in AlSi12 parts processed by SLM that were then subjected to heat treatments at different temperatures, ranging from 200 °C to 500 °C, in order to investigate how residual stresses and microstructure changes vary with heat treatment temperatures.

Estimation of Correct Long-Seam Mismatch Using FEA to Compare the Measured Strain in a Non-Destructive Testing of a Pressurant Tank

This paper discusses the design criterion of a pressurant steel tank made of HSLA 15CDV6 and proof pressure test (PPT) as a non-destructive examination. An inverse Ramberg-Osgood relation is used to represent the stress-strain curve of the material. Elasto-plastic finite element analysis (FEA) has been carried out to examine the adequacy of the design. Experimental stress analysis has been carried out from the measured strains and found maximum effective stress is at LS joint (max. measured strain location). Strain obtained from FEA is compared reasonably well with the proof pressure test (PPT) data at most of the strain gauge locations except at one long-seam (LS) joint. So, to explain the causes of difference in strains near one LS, parametric studies have been performed in a 3D FEA with varying LS mismatch to find the correct mismatch as a reverse engineering problem. It is found that a mismatch value of 0.9 mm will give the required strain at PPT, which is measured only 0.4 mm. The failure pressure estimated through nonlinear FEA/analytical expressions found to meet the design.

Effect of crystallization on the macro and micro residual stress of enamel coating

In this paper, we investigate microstructural and mechanical properties of enamel coating after different heat treatment periods. The results show that the refractory BaAl2Si2O8, CaAl2Si2O8 and MgCr2O4 crystals precipitate from parent enamel, and crystallization volume fraction reaches saturation at 40 % after heat treatment 32 h. Moreover, from the experimental and theoretical analysis of residual stress, the macro and micro compressive residual stresses increase with increasing the crystallized volume fraction. And, the continuous macro compressive residual stress and small-scale microstructure inhomogeneities could significantly lead to the shear stress concentration near the enamel coating surface, which results in the typical fish-scaling failure of enamel. Meanwhile, we also find that a slit method with geometric phase analysis (GPA) under focused ion beam scanning electron microscopy (FIB/SEM) system could more reliably characterize residual stress of enamel coating because of phase transformation than traditional X-ray diffraction (XRD) method.