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principal directions. Thus, Measurements Group (2000) suggests that when the directions of the principal strains are unknown, a rectangular or delta rosette is always required and the rosette can be installed without regard to orientation. With respect to the above guidelines, Khan and Hsiao (1984) have used strain gauge rosettes to measure stress concentration in the intersection region of straight cylinder shells. Three element rosettes have been used in the immediate vicinity of the intersection region where appreciable values of shear stresses are expected. Two element rosettes or tee rosettes are used at locations which are not in the immediate vicinity of the intersection because before that they measure the magnitude of shear stresses which are small even around the intersection region. In the process of investigating the feasibility of extending onshore composite repair techniques to offshore risers by developing integrated analytical and experimental methods, Alexander (2007a) installed tee strain rosettes on the flat bottomed notch steel pipe as well as on the outside of the repair. Under different series of tests, such as pressure test, pressure-tension test and pressure-tension bending test, Alexander (2007a) claims that the gauges which have provided the greatest information, relative to the performance of the repair, are those located in the centre of the corrosion groove beneath the repair. Those gauges also indicate the level of reinforcement provided by the composite material in terms of load being transferred from the steel to the composite material. However, the results are still sceptical because, according to Measurements Group (2000), for this type of application the rectangular strain gauge (RSG) rosette is more suitable than the tee rosette. In a current research study on a new bonding integrity of a composite repair system using the experimental approach, Murad et al. (2011) have made a preliminary study, firstly in terms of choosing the right type of strain gauges before carrying out the experiment. Based on the above and other literature, RSG rosettes have been chosen since the experimental pipe specimen contains some irregularities such as notch and welded joints. This method has shown the ability to evaluate the actual level of load transfer despite being in the elastic region and will be discussed further in the following chapters. Actually, other techniques such as the photo elastic method can provide an 50
accurate simulation of loading especially in the study of stress concentration, as explained by Bahai and Esat (1994). However, this method is expensive and time- consuming and can only be justified for validation purposes or when strain gauging is impractical to be installed, for example in the study of complex stress distribution in threaded connectors. There are also a few important parameters that need to be highlighted in this experimental approach section. Firstly, the repair system that is used in this experiment is fully qualified to the relevant standards governing the use of composite repairs, ISO/TS 24817 and ASME PCC-2 (Frost, 2010a). Secondly, a package of knowledge skill and competency in installing strain gauges, and acquiring data using the Compact Rio system/Labview software is considered to be one of the main ingredients to produce more accurate and sensible data. With reliable experimental data, the numerical result using ABAQUS can be validated accordingly and a completely integrated SHM approach can be implemented successfully. 2.9 Why is SHM important in the composite repair? Lesmana (2010) reports there are two application techniques that are available for the repair of pipelines using composite: 1) Wet wrap application (wet applied cloth) 2) Full cure application Wet wrap application: A flexible cloth, woven from E-glass (e.g. based on the product of Technowrap from Walker Technical Resources Ltd) or carbon (e.g. Black Diamond from Citadel Technologies) is impregnated with resin on the repair site. The fibre provides the strength needed in the repair and the resin provides the bonding matrix to hold the repair in place. 51
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CRANFIELD UNIVERSITY MAHADI ABD MUR
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ABSTRACT One of the most common pro
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TABLE OF CONTENTS ABSTRACT ........
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3.7.1 Introduction ................
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5.6 Summary and Conclusions .......
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Figure 3.1: Schematic diagram of th
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Figure 5.4: The average temperature
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NOMENCLATURES ACFM Alternating Curr
Page 21 and 22: 1 INTRODUCTION One of the most comm
Page 23 and 24: 1.1 Objectives Knowing this backgro
Page 25 and 26: The methodology of this integrated
Page 27 and 28: Chapter 6 contains the summary and
Page 29 and 30: period of the major part of the exi
Page 31 and 32: Figure 2.2: Reported interest in de
Page 33 and 34: Figure 2.4: Dent damage caused by v
Page 35 and 36: presented current practices, recent
Page 37 and 38: Energy Workforce Sdn Bhd (2011) cla
Page 39 and 40: available provides real time detect
Page 41 and 42: 2.3.3 Reliability Analysis of Infor
Page 43 and 44: Figure 2.9: Pipeline failure probab
Page 45 and 46: 2.3.3.1 NDT Reliability and POD cur
Page 47 and 48: increase in the yield limit of stee
Page 49 and 50: the SCC assessment in their integri
Page 51 and 52: Manufacturers such as Walkers Techn
Page 53 and 54: Company L.P, 2005); Aquawrap ® pro
Page 55 and 56: monitoring, inspection, and damage
Page 57 and 58: 2.6.2 Aims of Structural Health Mon
Page 59 and 60: Figure 2.16: Application fields and
Page 61 and 62: egistered by the piezoelectric sens
Page 63 and 64: discretization error. Round-off err
Page 65 and 66: notches and Neuber‘s is better fo
Page 67 and 68: maximum local stress at discontinui
Page 69: De Carvalho (2005) concludes that t
Page 73 and 74: Based on the above facts, the opera
Page 75 and 76: 3 FINITE ELEMENT ANALYSIS (FEA) IN
Page 77 and 78: Figure 3.2: Schematic diagram of th
Page 79 and 80: In this modelling work (i.e. compos
Page 81 and 82: This partition toolset also helps u
Page 83 and 84: Figure 3.6: Mesh control using Swee
Page 85 and 86: Figure 3.7: Schematic representatio
Page 87 and 88: discretization. Therefore, in this
Page 89 and 90: According to Staten et al. (2010b),
Page 91 and 92: 3.5 The influence of pressure on th
Page 93 and 94: each pressure value remains constan
Page 95 and 96: Axial Stress, σa (S22) was referre
Page 97 and 98: Figure 3.14 shows a graph of analyt
Page 99 and 100: the notch defect is found to be in
Page 101 and 102: One of the contributions of this st
Page 103 and 104: Table 3.4: Convergence tests on var
Page 105 and 106: Figures 3.16 and 3.17 show that the
Page 107 and 108: Figure 3.20 shows that as the relat
Page 109 and 110: 3.7.4 Concluding Remarks A biaxial
Page 111 and 112: yarns change and lateral contact be
Page 113 and 114: For predicting E2 and Gl2, a number
Page 115 and 116: Where: Ar = weight of one sheet of
Page 117 and 118: Where; The Stiffness matrix is trad
Page 119 and 120: simulations for the hoop strain at
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Figure 3.24: Finding the hoop stres
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Table 3.8: The effect of repair len
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four up to 18 layers. In this study
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hoop and axial stress concentration
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Table 3.11: Predicted Elastic Const
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Table 3.13: Axial Stress v/s L/W ra
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Hoop Stress (MPa) Figure 3.3: Hoop
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However, Frost (2008) and Alexander
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Table 3.17: Ratio of Axial Stress N
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axial load (e.g. buried pipelines t
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3.10 Numerical Strain Analysis of C
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Figure 3.36 shows the contours befo
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Stress Concentration Factor 2 1.8 1
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In fact, for Notch 40 with 18 plies
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this second approach (i.e. the expe
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4.2.2 Strain Gauge Selection and Cr
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Finally, a method used to calculate
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Where, and are the maximum and mini
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should be between 20 and 28 bar and
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welded weld neck flange at both end
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Figure 4.7: Sensor and heating elem
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Figure 4.9: A summary of data acqui
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One of the objectives of doing this
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Figure 4.14: A schematic diagram of
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Table 4.1: Strain gauge readings at
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microstrain 3.00E-04 2.50E-04 2.00E
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However, the axial load transfer is
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Mircostrain 500 450 400 350 300 250
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Since the defect is not a flat notc
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Again, the epoxy resin plays a sign
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Table 4.4: Study at the defect area
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Mircostrain 300 250 200 150 100 50
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Mircostrain 600 500 400 300 200 100
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14.25% in hoop strain and 23.5% in
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consideration for the selection of
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5.4 Methodology of Thermal Expansio
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Figure 5.1: Some preventive measure
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5.4.1 The Fundamentals of the Therm
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5.5 Analysis of Results 5.5.1 The t
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Thermal Output (strain ) 0.0002 0.0
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(Strain ,ε) Figure 5.12: Coefficie
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(Strain ,ε) 0.0002 0.00018 0.00016
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Table 5.1: The strain readings afte
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maximum shear strain increase as th
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The above results show that shear s
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shear strains becomes more stable a
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for future safe design and operatio
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has been fully cured. Poor surface
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6.3 Primary PhD Achievements The ea
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In Chapter 5, the CTE was determine
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ASM International (2002), "Thermal
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Bucinell, R. B. (2001), Calculating
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Proceedings of OMAE'01 20th Interna
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Greenwood, R. (2002), UKOPA Pipelin
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Kotrechko, S. A., Krasovskii, A. Y.
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Mousavi, S. E., Xiao, H. and Sukuma
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Raju, I. S. and Newman, J. C. (1986
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Tennyson, R. C. and Mufti, A. A. (2
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Xue, L., Widera, G. E. O. and Sang,
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General Technical Specifications: T
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Photos of the Design and Build of t
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Composite Installation Process usin
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APPENDIX 3 - STRAIN GAUGE INSTALLAT
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Figure 7: Mylar tape was stuck onto
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Figure 19: Repeating the above proc
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2) Electrical Insulation Test Resul
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