A numerical approach to determine fiber orientations around geometric discontinuities in designing against failure of GFRP laminates

2019 ◽  
Vol 10 (3) ◽  
pp. 371-379 ◽  
Author(s):  
Roselita Fragoudakis
Keyword(s):  
Stress Concentration ◽  
Plastic Zone ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Load Condition ◽  
Content Type ◽  
Geometric Discontinuities ◽  
Failure Theories ◽  
Laminated Structures ◽  
Minimum Moment

Purpose Determining fiber orientations around geometric discontinuities is challenging and simultaneously crucial when designing laminates against failure. The purpose of this paper is to present an approach for selecting the fiber orientations in the vicinity of a geometric discontinuity; more specifically round holes with edge cracks. Maximum stresses in the discontinuity region are calculated using Classical Lamination Theory (CLT) and the stress concentration factor for the aforementioned condition. The minimum moment to cause failure in a lamina is estimated using the Tsai–Hill and Tsai–Wu failure theories for a symmetric general stacking laminate. Fiber orientations around the discontinuity are obtained using the Tsai–Hill failure theory. Design/methodology/approach The current research focuses on a general stacking sequence laminate under three-point bending conditions. The laminate material is S2 fiber glass/epoxy. The concepts of mode I stress intensity factor and plastic zone radius are applied to decide the radius of the plastic zone, and stress concentration factor that multiplies the CLT stress distribution in the vicinity of the discontinuity. The magnitude of the minimum moment to cause failure in each ply is then estimated using the Tsai–Hill and Tsai–Wu failure theories, under the aforementioned stress concentration. Findings The findings of the study are as follows: it confirms the conclusions of previous research that the size and shape of the discontinuity have a significant effect on determining such orientations; the dimensions of the laminate and laminae not only affect the CLT results, but also the effect of the discontinuity in these results; and each lamina depending on its position in the laminate will have a different minimum load to cause failure and consequently, a different fiber orientation around the geometric discontinuity. Originality/value This paper discusses an important topic for the manufacturing and design against failure of Glass Fiber Reinforced Plastic (GFRP) laminated structures. The topic of introducing geometric discontinuities in unidirectional GFRP laminates is still a challenging one. This paper addresses these issues under 3pt bending conditions, a load condition rarely approached in literature. Therefore, it presents a fairly simple approach to strengthen geometric discontinuity regions without discontinuing fibers.

scholarly journals Selection of fiber orientation around geometric discontinuities in designing against failure of GFRP laminates

2018 ◽  
Vol 188 ◽  
pp. 01010
Author(s):  
Roselita Fragoudakis
Keyword(s):  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Fiber Orientation ◽  
Failure Theory ◽  
Geometric Discontinuities ◽  
Lamination Theory ◽  
Failure Theories ◽  
Maximum Stresses ◽  
Minimum Moment ◽  
Selection Of

Determining fiber orientation around geometric discontinuities is challenging and simultaneously crucial when designing laminates against failure. This study presents an approach for selecting the fiber orientations in the vicinity of a geometric discontinuity. Maximum stresses in the discontinuity region are calculated using Classical Lamination Theory and the stress concentration factor. The use of the Tsai-Hill and Tsai-Wu failure theories estimate the minimum moment to cause failure in a lamina. Fiber orientations around the discontinuity are obtained using the Tsa-Hill failure theory.

scholarly journals A Study on The Effect Of Defect Location On Stress In Bending Pipe

2021 ◽  
Vol 12 (6) ◽  
pp. 802-806
Author(s):  
Jin-Bong KIM
Keyword(s):  
Boundary Condition ◽  
Stress Concentration ◽  
Plastic Zone ◽  
Boundary Conditions ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Stress Difference ◽  
Secondary Root ◽  
Defect Location ◽  
Minimum Value

In this study, the stress that generated when the first or second root of a corrugated pipe is defective is analyzed. The model is analyzed using F.E.M. code. The boundary conditions of deflection or torsion on the opposite side of the defect in the corrugated pipe are changed. The effect of the defect is evaluated using the change of the stress magnitude and the stress concentration factor(K) according to those conditions. As a result of comparing the stress magnitude, K around the flaw at the secondary root is larger than K around the flaw at the first root. Based on the position of the defect, the stress difference in the 1st root increases depending on the boundary condition of bending deflection. However, when the 2nd root is defective, the stress magnitude is similar in both cases regardless of the bending deflection. The magnitude of the stress generated in the corrugated pipe is the highest when the second root is defective. And the stress magnitude is the lowest when there is no defect. In the absence of defects, the stress gradually increases after the stress reaches the minimum value as the amount of deformation increases. However, if there is a defect, stress continues to increase, and when it passes through the plastic zone, the stress gradually increases.

Isogeometric Analysis Prediction of Stress Concentration Factor of Trivariate NURBS-Based Rectangular Plate with Central Elliptical Hole

2014 ◽  
Vol 556-562 ◽  
pp. 742-746
Author(s):  
Yusuf Olatunbosun Tafa ◽  
Gang Zhao ◽  
Wei Wang
Keyword(s):  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Isogeometric Analysis ◽  
Concentration Factor ◽  
Three Dimensional ◽  
Elliptical Hole ◽  
The Body ◽  
Geometric Discontinuities ◽  
Trivariate Nurbs ◽  
Good Agreement

Experimental, analytical and finite element techniques are commonly known methods used in determining highly localized stress occurring in the body under loading as a result of geometric discontinuities. In this study, we use NURBS-based isogeometric analysis (IGA) to investigate the stress concentration factor (SCF) on three-dimensional geometry with discontinuity feature. The results show that IGA technique is in good agreement with analytical values, thus providing a more effective realistic way of determining SCF.

Analysis of strain and stress concentrations in micro-lattice structures manufactured by SLM

2019 ◽  
Vol 26 (2) ◽  
pp. 370-380 ◽  
Author(s):  
Laura Boniotti ◽  
Stefano Foletti ◽  
Stefano Beretta ◽  
Luca Patriarca
Keyword(s):  
Mechanical Properties ◽  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Image Correlation ◽  
Stress Concentrations ◽  
Content Type ◽  
Lattice Materials ◽  
Geometrical Imperfections

Purpose Additive manufacturing (AM) enables the production of lightweight parts with complex shapes and small dimensions. Recent improvements in AM techniques have allowed a significant growth of AM for industrial applications. In particular, AM is suitable for the production of materials shaped in lattice, which are very attractive for their lightweight design and their multi-functional properties. AM parts are often characterised by geometrical imperfections, residual porosity, high surface roughness which typically lead to stress/strain localisations and decreasing the resistance of the structure. This paper aims to focus on the study of the effects of geometrical irregularities and stress concentrations derived from them. Design/methodology/approach In this paper, several technique were combined: 3D tomography, experimental tests, digital image correlation and finite elements (FE) models based on both the as-designed and the as-manufactured geometries of lattice materials. The Digital Image Correlation technique allowed to measure local deformations in the specimen during the experimental test. The micro-computed tomography allowed to reconstruct the as-manufactured geometries of the specimens, from which the geometrical quality of the micro-structure is evaluated to run FE analyses. Findings Experimental and numerical results were compared by means of a stress concentration factor. This factor was calculated in three different specimens obtained from three-different printing processes to compare and understand their mechanical properties. Considering the as-designed geometry, it is not possible to model geometrical imperfections, and a FE model based on an as-manufactured geometry is needed. The results show that the mechanical properties of the printed samples are directly related to the statistical distribution of the stress concentration factor. Originality/value In this work, several techniques were combined to study the mechanical behaviour of lattice micro-structures. Lattice materials obtained by different selective laser melting printing parameters show different mechanical behaviours. A stress concentration factor can be assumed as a measure of the quality of these mechanical properties.

scholarly journals A novel thread connection structure of slimehole drilling tool in ultra-deep natural gas well

2021 ◽  
Vol 104 (2) ◽  
pp. 003685042110264
Author(s):  
Zhang Ying ◽  
Lian Zhanghua ◽  
Gao Anqi ◽  
Yang Kun
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Sensitivity Coefficient ◽  
Notch Sensitivity ◽  
Sensitivity Factor ◽  
Drilling Tool ◽  
Gas Well ◽  
Thread Connection

The thread connection’s root fillet radius of 0.038″ size is the greatest weakness of the API NC type joints and thread. During the slimehole drilling, especially in the deep and ultra-deep gas well, its stress concentration factor and notch sensitivity factor are very high A novel thread connection design (TM) of a drilling tool is proposed to decrease the fatigue failure of the slimehole drilling tool in the deep and the ultra-deep gas well in the Tarim oilfield China. The novelty in the TM thread structure is, reducing the threads per inch, extending the distance from the last engaged thread to the external shoulder of the pin and adding three threads to the conventional connection. The novel thread connection will improve the slimehole drilling tool’s anti-fatigue life due to its improved elasticity and rigidity. Furthermore, the TM can transfer the maximum stress at the connection root to the loaded surface, which can effectively lower the fatigue notch’s sensitivity coefficient. In this paper, the finite element method (FEM) is applied to carry out the detailed comparative analysis of the TM with existing thread connection NC38, TX60 and TH90. The TM has the lowest stress concentration factor and fatigue notch sensitivity coefficient, so its anti-fatigue life is the highest. In addition, TM is manufactured and is tested at Tarim oilfield in China.

Stress Concentration of Periodic Collinear Square Holes in an Infinite Plate in Tension

2015 ◽  
Vol 137 (5) ◽  
Author(s):  
Changqing Miao ◽  
Yintao Wei ◽  
Xiangqiao Yan
Keyword(s):  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Infinite Plate ◽  
Numerical Approach ◽  
Numerical Examples ◽  
Calculated Stress ◽  
Bueckner’S Principle

A numerical approach for the stress concentration of periodic collinear holes in an infinite plate in tension is presented. It involves the fictitious stress method and a generalization of Bueckner's principle. Numerical examples are concluded to show that the numerical approach is very efficient and accurate for analyzing the stress concentration of periodic collinear holes in an infinite plate in tension. The stress concentration of periodic collinear square holes in an infinite plate in tension is studied in detail by using the numerical approach. The calculated stress concentration factor is proven to be accurate.

Fracture of Inoculated Iron Under Biaxial Stresses

1955 ◽  
Vol 22 (2) ◽  
pp. 172-174
Author(s):  
I. Cornet ◽  
R. C. Grassi
Keyword(s):  
Cast Iron ◽  
Stress Concentration ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Gray Cast Iron ◽  
Energy Criterion ◽  
Gray Cast ◽  
Published Data ◽  
Thin Wall ◽  
As Stress

Abstract Data are presented on the fracture of inoculated-iron thin-wall tubes, investigated under various ratios of axial to tangential stress, ranging from pure tension to pure compression. These data are consistent with published data on gray cast iron. It may be assumed that in cast-iron, plates of friable graphite in an iron matrix, act like solid iron with respect to compressive stresses, but they act as stress-concentrating cavities with respect to tensile stresses. This gives a stress-concentration factor, which is easily determined experimentally. Stress-concentration factors obtained were 3.2–3.3 for gray cast iron, and 2.4–2.5 for inoculated cast iron. A distortion-energy criterion for fracture, modified by this stress-concentration factor, is consistent with the experimental data. It appears that the concentration of the dispersed graphite, and the shape and size of this brittle phase, affect the fracture strength under combined stresses.

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