Comparison of Calculated Crack Growth Values Using Unloading Compliance and d-c EP During SENT Testing

2016 ◽  
Author(s):  
Y. Hioe ◽  
S. Kalyanam ◽  
G. M. Wilkowski
Keyword(s):  
Crack Growth ◽  
Fracture Resistance ◽  
Structural Integrity ◽  
The Arctic ◽  
Test Results ◽  
Weld Defect ◽  
Pros And Cons ◽  
Unloading Compliance ◽  
Exxon Mobil

SENT testing has become increasingly important in the characterization of the base, girth weld, and HAZ structural integrity for pipelines that are operational in the low temperature regions, such as the arctic. While the SENB and CT specimens have been used traditionally in the fracture toughness characterization and assessment of pipeline materials and welds, the SENT specimen is better representative of the constraint behavior of surface cracks found in service. Further, the SENT specimen is closer in representing the ductile-to-brittle transition temperature region for the pipe operation. For strain-based design, ECA, and stress-based fracture analyses of girth weld defects, SENT test results have been found to be more representative of the constraint of a surface crack in a pipe and hence better reflects the material toughness. Typically the CTOD as a function of crack growth is used in girth weld defect analyses, but J-R curves can be calculated at the same time. While several procedures for SENT testing (DNV, Exxon Mobil, CANMET) are currently used in the industry and are based on reliable constitutive behavior, plasticity, and fracture theories and experimental methods, more recently a British Standard (BS8571:2014) has been published. In these procedures, either the d-c EP method or the unloading compliance technique are used to determine the start of ductile tearing and crack growth to arrive at fracture resistance CTOD-R and J-R curves. This paper presents results from comparisons of crack growth predictions where in both techniques were used simultaneously when conducting the SENT tests. Other unique aspects of the comparative methodologies, pros and cons of each of the two methods, guidelines for fracture resistance curve development from SENT testing, and its impact on girth weld, HAZ testing are also discussed.

Improved Incremental J-Integral Equations for Determining Crack Growth Resistance Curves

2012 ◽  
Vol 134 (5) ◽  
Author(s):  
Xian-Kui Zhu
Keyword(s):  
Fracture Mechanics ◽  
Crack Growth ◽  
Integral Equations ◽  
Structural Integrity ◽  
Test Procedure ◽  
Fracture Toughness Test ◽  
J Integral ◽  
Integrity Assessment ◽  
Growth Increments ◽  
Unloading Compliance

The J-integral resistance curve is the most important material properties in fracture mechanics that is often used for structural integrity assessment. ASTM E1820 is a commonly accepted fracture toughness test standard for measuring the critical value of J-integral at the onset of ductile fracture and J-R curve during ductile crack tearing. The recommended test procedure is the elastic unloading compliance method. For a stationary crack, the J-integral is simply calculated from the area under the load-displacement record using the η-factor equation. For a growing crack, the J-integral is calculated using the incremental equation proposed by Ernst et al. (1981, “Estimations on J-integral and Tearing Modulus T From a Single Specimen Test Record,” Fracture Mechanics: Thirteenth Conference, ASTM STP 743, pp. 476–502) to consider the crack growth correction. For the purpose of obtaining accurate J-integral values, ASTM E1820 requires small and uniform crack growth increments in a J-R curve test. In order to allow larger crack growth increments in an unloading compliance test, an improved J-integral estimation is needed. Based on the numerical integration techniques of forward rectangular, backward rectangular, and trapezoidal rules, three incremental J-integral equations are developed. It demonstrates that the current ASTM E1820 procedure is similar to the forward rectangular result, and the existing Garwood equation is similar to the backward rectangular result. The trapezoidal result has a higher accuracy than the other two, and thus it is proposed as a new formula to increase the accuracy of a J-R curve when a larger crack growth increment is used in testing. An analytic approach is then developed and used to evaluate the accuracy of the proposed incremental equations using single-edge bending and compact tension specimens for different hardening materials. It is followed by an experimental evaluation using actual fracture test data for HY80 steel. The results show that the proposed incremental J-integral equations can obtain much improved results of J-R curves for larger crack growth increments and are more accurate than the present ASTM E1820 equation.

Crack Growth Life Estimating for MSD Panel

2008 ◽  
Vol 33-37 ◽  
pp. 175-180 ◽  
Author(s):  
Jian Yu Zhang ◽  
Rui Bao ◽  
Li Bin Zhao ◽  
Li Ping Long ◽  
Bin Jun Fei
Keyword(s):  
Crack Growth ◽  
Structural Integrity ◽  
Relative Size ◽  
Initial Crack ◽  
Fast Method ◽  
Test Results ◽  
Multiple Site Damage ◽  
Fatigue Crack Growth Life ◽  
Aircraft Panels ◽  
Initial Cracks

The problem of multiple site damage (MSD) has got more attention in ageing structures. Cumulative effects of interacting cracks may significantly degrade the damage tolerance capacity of structures. Cracks caused by MSD are extremely difficult to detect and greatly reduce the residual strength, fatigue life and overall structural integrity of aircraft panels. This paper presents a simple numerical method, which use the principles of fracture mechanics and the computation results, to predict the fatigue crack growth life of MSD structure. Comparing with calculating crack growth life cycle by cycle, this method will save much time. To verify the validity of the proposed method, experiment was conducted and reported with simulation specimen of representative MSD structure with 5 details. The comparison between the calculated a-N curves and the crack growth lives and the test results shows that the prediction result with this fast method is acceptable. A discussion was carried out by numerical analysis; in with typical MSD structures with different initial crack length were adopted. Crack interaction effect was found obviously, but it occurred mainly in the last part of the crack growth lives. The relative size of MSD cracks depends significantly on the distribution of the initial cracks.

Evolution of Plasticity in Relation to Ductile Tearing in 304(L) Stainless Steel

2010 ◽  
Author(s):  
Andrew P. Wasylyk ◽  
Andrew H. Sherry
Keyword(s):  
Fracture Toughness ◽  
Plastic Zone ◽  
Crack Growth ◽  
Structural Integrity ◽  
Plastic Zone Size ◽  
Compact Tension ◽  
Image Correlation ◽  
Ductile Tearing ◽  
Integrity Assessment ◽  
Unloading Compliance

In the structural integrity assessment of structures containing defects, ductile tearing and plastic collapse are treated as competing failure mechanisms. The validity of fracture toughness measurements in test specimens is limited by the development of plasticity ahead of the crack tip. Compact Tension (CT) specimens are commonly used to characterise the ductile fracture toughness. Two sizes of CT specimens (thickness 25 and 15mm) were tested using the unloading compliance technique and the J-Resistance curve characterised. Concurrently, the development of the plastic zone was monitored on the surface of specimens using digital image correlation. This enabled the plastic zone size to be correlated with the evolution of crack growth. It was found that in both specimens no crack growth had occurred prior to plastic yielding of the un-cracked ligament on the specimen surface.

Determination of the Region of Steady-State Crack Growth From Impact Tests

2002 ◽  
Author(s):  
Gery M. Wilkowski ◽  
David L. Rudland ◽  
Yong-Yi Wang ◽  
David Horsley ◽  
Alan Glover ◽  
...  
Keyword(s):  
Steady State ◽  
Ductile Fracture ◽  
Crack Growth ◽  
Fracture Resistance ◽  
Crack Tip ◽  
Opening Angle ◽  
Test Results ◽  
Crack Tip Opening Angle ◽  
Linepipe Steels ◽  
Crack Tip Opening

Large-diameter gas pipelines typically have a design requirement to ensure that the toughness is sufficient to avoid brittle or ductile fractures from occurring. New pipeline design requirements with richer gases, higher-grade steels, higher operating pressures, and in some cases lower operating temperatures require considerable extrapolation of the current ductile fracture design equations. To obtain a better understanding of ductile fracture arrest toughness, TCPL has funded efforts to assess the steady-state fracture toughness from specimens that can be used in mill applications. This paper reviews past efforts to assess the regions of steady-state ductile crack growth in test specimens, as well as current test results from numerous highly instrumented impact specimens. The new test results were for X52, X70, and X80 linepipe steels, whereas the past efforts were from linepipe steels, aerospace materials, as well as ferritic and austenitic nuclear piping steels. All of these results show that there is a limited region over which the steady-state fracture resistance can be determined. The fracture energy associated with steady-state fracture is the total energy minus; (1) the energy associated with initiation of the crack (including indentation energy and global yielding of the specimen), (2) the transient crack growth from initiation to reaching steady-state fracture, and (3) a non-steady-state fracture region at the end of the test record. Instrumented load versus load-line displacement data were linked to high-speed digital video data of the crack growth, crack-tip-opening angle (within 2 mm of the crack tip), and crack-mouth-opening displacement. These data allowed for comparison of J-R curves and crack-tip-opening angle values during crack growth to help determine the regions of steady-state crack growth. The results from these efforts are an important consideration in the development of a single test specimen method that can be used for determining the ductile fracture resistance of high-strength and high-toughness linepipe steels.

Improved Incremental J-Integral Equation for Determining Crack Growth Resistance Curves

2010 ◽  
Author(s):  
Xian-Kui Zhu ◽  
Brian N. Leis
Keyword(s):  
Integral Equation ◽  
Crack Growth ◽  
Structural Integrity ◽  
Test Procedure ◽  
Fracture Toughness Test ◽  
J Integral ◽  
Integrity Assessment ◽  
Growth Increments ◽  
Specimen Test ◽  
Unloading Compliance

The J-integral resistance curve is the most important material property used in structural integrity assessment. ASTM E1820 is a commonly used fracture toughness test standard for measuring the critical value of J-integral at the onset of ductile fracture and J-R curve. The recommended test procedure is the elastic unloading compliance method where multiple points are obtained from a single specimen test. For a stationary crack, the J-integral is simply calculated from the area under the load-displacement record using the η-factor equation. For a growing crack, the J-integral is calculated using the incremental equation proposed by Ernst et al. (1981) to consider the crack growth correction. In order to obtain accurate J-integral values, ASTM E1820 requires small and uniform crack growth increments. To allow larger crack growth increments in the unloading compliance test, an improved J-integral estimate equation is needed. Thus, this paper proposes a new incremental J-integral equation for determining J-R curves. An analytic approach is then developed and used to evaluate the accuracy of the proposed incremental equation using single edge bending and compact specimens for different hardening materials. Followed is an experimental evaluation using actual fracture test data for HY80 steel. The results show that the proposed incremental J-integral equation can obtain much improved results of J-R curves for larger crack growth increments, and thus is more accurate than the present ASTM E1820 equation.

Neuropharmacological Characterization of Dioclea altissima Seed Lectin (DAL) in Mice: Evidence of Anxiolytic-like Effect Mediated by Serotonergic, GABAergic Receptors and NO Pathway

2020 ◽  
Vol 26 (31) ◽  
pp. 3895-3904
Author(s):  
João R.C. Araújo ◽  
Adriana R. Campos ◽  
Marina de Barros M.V. Damasceno ◽  
Sacha A.A.R. Santos ◽  
Maria K.A. Ferreira ◽  
...  
Keyword(s):  
Structural Integrity ◽  
Elevated Plus Maze ◽  
Biological Activities ◽  
Plant Lectins ◽  
Plus Maze ◽  
Marble Burying ◽  
Gabaergic Receptors ◽  
The Central Nervous System ◽  
Hole Board

Background: Plant lectins have shown promising biological activities in the central nervous system (CNS). Objective: This study evaluated the effect of DAL, a lectin isolated from the seeds of the Dioclea altissima species, having binding affinity to D-glucose or D-mannose residues, on mice behavior. Methods: Mice (n=6/group) were treated (i.p.) with DAL (0.25, 0.5 or 1 mg/kg) or vehicle and subjected to several tests (open field/OFT, marble-burying/MBT, hole-board/HBT, elevated plus maze/PMT, tail suspension/ TST, forced swimming/FST or rotarod/RRT). Pizotifen, cyproheptadine, flumazenil, L-NAME, 7-NI, Larginine or yohimbine were administered 15 min before DAL (0.5 mg/kg) and the animals were evaluated on PMT. It was also verified whether the DAL effect depended on its structural integrity and ability to interact with carbohydrates. Results: The results showed there were no neurobehavioral changes in the mice at the RRT, FST and locomotion in the OFT. DAL (0.25, 0.5 or 1 mg/kg) increased the behavior of grooming and rearing in the OFT, head dips in the HBT, pedalling in the TST and decreased the number of marbles hidden in the MBT. In the PMT, DAL (0.25, 0.5 and 1 mg/kg) and Diazepam increased the frequency of entries in the open arms and the time of permanence in the open arms without affecting the locomotor activity. The effect of DAL was dependent on carbohydrate interaction and protein structure integrity and it prevented by pizotifen, cyproheptadine, flumazenil, L-NAME and 7-NI, but not by L-arginine or yohimbine. Conclusion: DAL was found to have an anxiolytic-like effect mediated by the 5-HT and GABAergic receptors and NO pathway.

Improved Compliance Solutions for C(T), SE(B) and Clamped SE(T) Specimens Including Side-Grooves, Varying Thicknesses and 3-D Effects

2014 ◽  
Author(s):  
Gustavo Henrique B. Donato ◽  
Felipe Cavalheiro Moreira
Keyword(s):  
Crack Growth ◽  
Plane Strain ◽  
Plane Stress ◽  
Potential Drop ◽  
Crack Size ◽  
Growth Conditions ◽  
Size Estimation ◽  
Unloading Compliance ◽  
Integrity Assessments ◽  
Elastic Unloading

Fracture toughness and Fatigue Crack Growth (FCG) experimental data represent the basis for accurate designs and integrity assessments of components containing crack-like defects. Considering ductile and high toughness structural materials, crack growing curves (e.g. J-R curves) and FCG data (in terms of da/dN vs. ΔK or ΔJ) assumed paramount relevance since characterize, respectively, ductile fracture and cyclic crack growth conditions. In common, these two types of mechanical properties severely depend on real-time and precise crack size estimations during laboratory testing. Optical, electric potential drop or (most commonly) elastic unloading compliance (C) techniques can be employed. In the latter method, crack size estimation derives from C using a dimensionless parameter (μ) which incorporates specimen’s thickness (B), elasticity (E) and compliance itself. Plane stress and plane strain solutions for μ are available in several standards regarding C(T), SE(B) and M(T) specimens, among others. Current challenges include: i) real specimens are in neither plane stress nor plane strain - modulus vary between E (plane stress) and E/(1-ν2) (plane strain), revealing effects of thickness and 3-D configurations; ii) furthermore, side-grooves affect specimen’s stiffness, leading to an “effective thickness”. Previous results from current authors revealed deviations larger than 10% in crack size estimations following existing practices, especially for shallow cracks and side-grooved samples. In addition, compliance solutions for the emerging clamped SE(T) specimens are not yet standardized. As a step in this direction, this work investigates 3-D, thickness and side-groove effects on compliance solutions applicable to C(T), SE(B) and clamped SE(T) specimens. Refined 3-D elastic FE-models provide Load-CMOD evolutions. The analysis matrix includes crack depths between a/W=0.1 and a/W=0.7 and varying thicknesses (W/B = 4, W/B = 2 and W/B = 1). Side-grooves of 5%, 10% and 20% are also considered. The results include compliance solutions incorporating all aforementioned effects to provide accurate crack size estimation during laboratory fracture and FCG testing. All proposals revealed reduced deviations if compared to existing solutions.

Optimization and characterization of flavonoids extracted from Cannabis sativa fibers

2021 ◽  
pp. 004051752110277
Author(s):  
Qilu Cui ◽  
Jiawei Li ◽  
Chongwen Yu
Keyword(s):  
Chemical Structure ◽  
Cannabis Sativa ◽  
Ethanol Concentration ◽  
Extraction Process ◽  
Test Results ◽  
Hemp Fiber ◽  
Hemp Fibers ◽  
Structure Surface ◽  
Degumming Process

In this paper, the extraction process of flavonoids from hemp fibers was studied. Response surface methodology (RSM) analysis of the extraction parameters indicated that optimized results would be ethanol concentration 76 vol.%, bath ratio 1:50, and reaction time 139 min; therefore, an optimal extraction rate of flavonoids of 0.2275% can be obtained. The chemical structure, surface morphology and element composition of flavonoid extracts were analyzed. The test results indicated that hemp extract contains flavonoids, which can be used to extract flavonoids from hemp fiber, so as to comprehensively develop hemp fiber and reduce the discharge of waste liquid in the traditional degumming process.

scholarly journals Design and Experimental Characterization of L-CADEL v2, an Assistive Device for Elbow Motion

Sensors ◽  
2021 ◽  
Vol 21 (15) ◽  
pp. 5149
Author(s):  
Marco Ceccarelli ◽  
Mykhailo Riabtsev ◽  
Axel Fort ◽  
Matteo Russo ◽  
Med Amine Laribi ◽  
...  
Keyword(s):  
Elderly People ◽  
Operating Performance ◽  
Assistive Device ◽  
Test Results ◽  
Experimental Characterization ◽  
Elbow Motion ◽  
Laboratory Prototype

An experimental characterization is presented for an improved version of a wearable assistive device for elbow motion. The design is revised with respect to requirements for elbow motion assistance, looking at applications both in rehabilitation therapies and exercising of elderly people. A laboratory prototype is built with lightweight, portable, easy-to-use features that are verified with test results, whose discussion is also provided as a characterization of operating performance.

scholarly journals Characterization of Mechanical Heterogeneity in Dissimilar Metal Welded Joints

Materials ◽  
2021 ◽  
Vol 14 (15) ◽  
pp. 4145
Author(s):  
He Xue ◽  
Zheng Wang ◽  
Shuai Wang ◽  
Jinxuan He ◽  
Hongliang Yang
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Welded Joints ◽  
Structural Integrity ◽  
Material Interfaces ◽  
Mechanical Heterogeneity ◽  
Finite Element Software ◽  
Dissimilar Metal ◽  
Stress Changes

Dissimilar metal welded joints (DMWJs) possess significant localized mechanical heterogeneity. Using finite element software ABAQUS with the User-defined Material (UMAT) subroutine, this study proposed a constitutive equation that may be used to express the heterogeneous mechanical properties of the heat-affected and fusion zones at the interfaces in DMWJs. By eliminating sudden stress changes at the material interfaces, the proposed approach provides a more realistic and accurate characterization of the mechanical heterogeneity in the local regions of DMWJs than existing methods. As such, the proposed approach enables the structural integrity of DMWJs to be analyzed in greater detail.

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