Assessment Of Residual Strength Research Articles

Comparison of surface and bulk analytical techniques for the distinct quantification of a moderate thermal pre-load on a carbon fibre reinforced plastic material

This work provides a comparison of analytical techniques to separately determine temperature and duration of a thermal pre-load on a polymer matrix composite as well as its residual strength. The aim is to assess selected techniques applied on surfaces and for bulk material to characterize incipient heat damage. The methods are ideally non-destructive such as infrared spectroscopy (IR). A destructive method for bulk material is represented by thermogravimetric analyses (TGA). TGA can be applied independent of accessible surfaces and inhomogeneous polymer distribution. Empirical correlations of the recorded data with mechanical properties allow the assessment of residual strength for a composite with unknown thermal history. Multivariate (chemometric) analyses provide reliable values for time and temperature (average deviation < 10 °C) of the thermal pre-load and residual interlaminar shear strength (average deviation < 5%). Bench top and hand held attenuated total reflection (ATR) and diffuse reflectance (DR) IR spectrometers provide similar accuracy. A commercially available composite (HexPly® M18-1/G939) was investigated. Infrared spectroscopy of bulk material after grinding is identified to provide a high potential of in-service use in aviation.

Assessment of residual ultimate strength of cracked steel plates under longitudinal compression

This paper numerically deals with the ultimate strength reduction characteristics of steel plate due to crack damage under longitudinal compression. A series of nonlinear finite element analyses was carried out with varying the length, location, and orientation angle of cracks to examine their effects on the ultimate strength of cracked steel plates. Three types of cracks, namely transverse crack, longitudinal crack and inclined crack, are considered in the present study. It was assumed that the cracks are through-thickness, having no contact between their faces and propagation of cracks is not considered in the present study. It is found that the minimum and the maximum ultimate strength values are obtained for the transverse crack and longitudinal crack cases respectively when the crack length is constant. The projected length of the crack normal to loading direction is an influential parameter to the ultimate compressive strength of plate with central inclined crack. Based on the numerical results, simple empirical formula as a function of crack projected length are proposed to predict the ultimate strength of plate with central inclined crack under longitudinal compression.

Assessment of residual strength of repaired solid laminate composite materials through mechanical testing

Robust residual strength test methods are critical for assessing the validity of new repair techniques for restoring strength to damaged composite laminates. In this study, the strength of pristine, damaged and repaired solid laminate composite material has been investigated by performing four different mechanical tests. Impact damage was imparted to carbon fibre epoxy resin specimens using a drop tower instrument. Specimens were repaired using a novel resin injection technique employing a low viscosity adhesive as the repair resin. The compressive strength of specimens was determined using compression after impact (CAI) and large-scale CAI test methods. Tensile tests were performed to obtain tensile strength. Flexural strength was evaluated by four-point bend tests. The thoroughness of each test method in determining the success of the repair was investigated. This study demonstrates that the strength restoring capacity of a repair method is subject to the test method used to assess the residual strength. The four-point bend test was shown to be the best preliminary test method for screening repair techniques as it is not affected by loading anomalies. However, design criteria should always be considered when choosing a residual strength test method for assessing repair validity.

Water absorption behavior and residual strength assessment of glass/epoxy and glass-carbon/epoxy hybrid composite

Present investigation is aimed to study the water absorption behaviour and evaluation of residual strength of glass fibre/epoxy (GE) and alternate plies of glass- carbon/epoxy (GCE) hybrid composite. Both the composite systems were exposed to water at 70°C. Specimens were weighed after certain time periods to study the water uptake kinetic. Flexural tests were conducted after 4, 100 and 450 hours of ageing to evaluate the effect of hot water ageing on the mechanical properties of these potential materials. The water uptake kinetic was found to follow Fickian diffusion kinetic for GE as well as GCE hybrid composite but the rate of diffusion was higher for GE composite over GCE composite. The water content was also higher in GE composite over GCE composite after 450 hours of ageing. Significant decrement in flexural strength was observed with the increase in ageing time. Presence of water in the composite also imparted significant embrittlement to the matrix as reflected in the decrease in strain at peak for both the composite systems.

Ultimate strength of locally damaged steel stiffened cylinders under axial compression

This paper focuses on the load-carrying behaviour of large diameter thin-walled stiffened cylinders with local damage when subjected to axial compressive loading. The case considered in this study corresponds to the residual strength assessment of columns of floating offshore structures with damage resulting from collisions with supply vessels. Numerical simulations of axial compression tests, which examine the collapse behaviour and the ultimate strength of ring- and orthogonally stiffened cylinders dented by a knife-edged indenter, are presented. The behaviour of eight small-scale ring-stiffened cylinders and four orthogonally stiffened cylinder specimens is analysed. Finite element analyses were performed using the ABAQUS FEA software package, and a close agreement between the experimental test results and the numerical predictions was achieved. To assess the factors influencing the reduction in ultimate strength under axial compression and to clarify the progressive collapse behaviour, further analyses were performed on design examples of ring- and orthogonally stiffened cylinders, considering both intact and damaged conditions.

Corrosion damage in WC/Co

Ken Brookes reviews the PM2014 Hardmetals Keynote Paper: ‘Corrosion damage in WC/Co cemented carbides: residual strength assessment and 3D FIB-FESEM tomography characterization.’

Interrelation of the acoustic Q-factor and strength in limestone

Under analysis is the experimental testing of interrelation between the limit of strength and the acoustic Q-factor in terms of Kasimov deposit limestone. The limit of strength is found using two procedures, namely, direct method and interpolation, which are compared. The authors illustrate the advantage of the acoustic Q-factor procedure in assessment of damage and residual strength of rocks as against the method of elastic wave velocities. The resultant relations can be used in assessment of residual strength and remaining life of pillars and roofs in underground excavations.

Failure analysis of high strength pipeline with single and multiple corrosions

Corrosion will compromise safety operation of oil and gas pipelines, accurate determination of failure pressure finds importance in residual strength assessment and corrosion allowance design of onshore and offshore pipelines. This paper investigates failure pressure of high strength pipeline with single and multiple corrosions using nonlinear finite element analysis. On the basis of developed regression equations for failure pressure prediction of high strength pipeline with single corrosion, the paper proposes an assessment procedure for predicting failure pressure of high strength pipeline with multiple corrosions. Furthermore, failure pressures predicted by proposed solutions are compared with experimental results and various assessment methods available in literature, where accuracy and versatility are demonstrated.

Corrosion damage in WC–Co cemented carbides: residual strength assessment and 3D FIB-FESEM tomography characterisation

The effect of corrosion damage on cemented carbides was investigated. The study included residual strength assessment and detailed fractographic inspection of corroded specimens as well as detailed 3D FIB-FESEM tomography characterisation. Experimental results point out a strong strength decrease associated with localised corrosion damage, i.e. corrosion pits acting as stress raisers, concentrated in the binder phase. These pits exhibit a variable and partial interconnectivity, as a function of depth from the surface, and are the result of heterogeneous dissolution of the metallic phase, specifically at the corrosion front. However, as corrosion advances the ratio between pit depth and thickness of damaged layer decreases. Thus, stress concentration effect ascribed to corrosion pits gets geometrically lessened, damage becomes effectively homogenised and relatively changes in residual strength as exposure time gets longer are found to be less pronounced.

Residual ultimate strength assessment of stiffened panels with locked cracks

The residual ultimate strength of stiffened panels with locked cracks under axial compressive loading is analyzed. The influences of various geometrical characteristics of cracks and panels, such as the length and the orientation angle of cracks, are investigated by the nonlinear finite element analysis. The cracks are prevented from further propagation by holes with a diameter of 2mm drilled at their tips. The finite element model has two bays in the longitudinal direction, employing periodical symmetrical boundary conditions at the ends of the loading edge. Beam tension test results are used to define the true stress–strain relationship of the material, which is used in the FE analyses to account for the nonlinear material property of steel.

Post-Fire Nondestructive Evaluation of a Prestressed Concrete Double-Tee Joist Roof

AbstractPrestressed concrete exhibits resistance to damage induced by fire and associated elevated temperatures, often permitting reuse of structural elements following exposure to accidental fire. However, prudent determination of suitability for reuse or rehabilitation of fire-damaged prestressed concrete requires a post-fire structural evaluation, which can be greatly aided by application of nondestructive testing for quantitative assessment of residual material properties, structural strength, and serviceability. In this study, a suite of nondestructive inspection and evaluation methods including visual documentation, camber surveying, penetration resistance testing, and impact-echo are applied to fire-damaged and unaffected double-tee joists of a precast, prestressed roof system. Qualitative and quantitative measures of fire damage obtained through the nondestructive tests are presented and strong correlations, in particular between longitudinal wave speed estimates obtained in impact-echo testing an...

화해된 콘크리트의 잔존 강도 평가에 있어서 충격-반향 기법의 적용성

이 연구에서는 화해된 콘크리트의 잔존 강도 평가에 있어서 충격-반향 기법의 적용성을 알아보고자 하였다. 화해를 모사하기 위해 콘크리트 실험체에 대한 표준 화재 온도 가열 시험을 실시하고, 화해된 콘크리트 실험체에 대해 충격-반향 응답 실험 및 압축 강도 실험을 실시하였다. 화해된 콘크리트의 충격-반향 응답 특성과 압축 강도의 잔존 특성을 분석하였으며, 또한 충격-반향 응답으로부터 구한 초음파 속도와 잔존 압축 강도와의 상관관계를 분석하였다. 연구 결과 화해된 콘크리트의 초음파 속도를 충격-반향 기법으로 신뢰성 있게 계측할 수 있으며, 또한 잔존 강도 평가에 충격-반향 기법을 유효하게 적용 가능하다는 것을 알 수 있었다. In this study, the applicability of impact-echo method for assessment of residual strength of fire-damaged concrete is investigated. A series of standard fire test is performed to obtain fire-damaged concrete specimens. Impact-echo tests are executed on the specimens and the responses are analyzed. Compressive strengths of the fire-damaged concrete are evaluated and correlated with the ultrasonic wave velocities determined from the impact-echo responses. The effectiveness of impact-echo based ultrasonic wave velocity measurement for assessment of residual strength of fire-damaged concrete is discussed.

보강재 본딩접합 복합재 적층판구조 피로손상 균열진전 수명예측에 대한 연구

본 연구에서는 적층판 시편의 피로손상 균열진전 시험결과와 적층보강판 구조의 응력강도 해석결과를 기초로 충격손상을 모사한 원공과 노치손상을 내재한 보강재 본딩접합 적층보강판 구조의 피로손상 균열진전 수명예측에 대하여 고찰하였다. 그리고 적층보강판 구조시편에 대한 손상허용 시험결과와 손상진전 수명예측 해석결과를 비교분석한 결과 손상균열 길이 변화에 따라 최종파단에 대한 잔여강도를 예측하고 손상허용성 평가를 할 수 있었다. The prediction and analysis procedure of fatigue damage crack growth life for a stiffener bonded composite laminate panel including center hole and edge notch damage, was studied. It was performed on the basis of fatigue damage growth test results on a laminated skin panel specimens and the analysis results of stress intensity factor for the stiffener bonded composite panel. According to the comparison between experimental test and prediction results of fatigue damage growth life, it was concluded that the residual strength and damage tolerance assessment can be carried out along to the edge notch crack growth.

A Numerical Study to Quantify Delamination Damage of Composite Structures Using an Inverse Method

Existing vibration-based approaches for damage detection are qualitative. This paper presents a novel two-step approach for characterisation of laminar damage, such as delamination in composites and thickness reduction in metallic structures due to corrosion damage. This new approach first employs a gapped smoothing method to determine the location from curvature data. The severity of damage is then determined in the second step using an inverse method by matching predictions of finite element analysis with deflection (or curvature) data pertinent to low-frequency vibrational response. An assessment of various approaches for computing curvature reveals that wavelet transform is a promising method for simultaneously removing noise and computing curvature. Numerical simulations show that this new two-step approach is capable of quantifying the size and severity of structural damage to be used as input for a residual strength assessment.

Assessment of residual ultimate strength for wide dented stiffened panels subjected to compressive loads

The aim of the present paper is to study the influence of a local dent on the collapse behaviour of stiffened panels. A quasi-static nonlinear finite element analysis is used to simulate the production of the local dent which will model the residual stress and the springback effect of the stiffened panels. The effect of residual stress caused by the local dent on the collapse behaviour of stiffened panels is investigated. The material properties used in the finite element analysis have been evaluated by tensile tests. Stiffened panel models with three and two bays in the longitudinal direction are used to prescribe appropriately boundary conditions for the middle bay. The relationship of the maximum indentation load and length of plate are almost linear and the springback displacements converge to a constant with increasing final depth of the dent. The residual stress caused by the indentation affects slightly the ultimate strength of the dented stiffened panels under consideration.

Numerical and simplified analytical methods for analysis of the residual strength of ship double bottom

This paper presents a numerical simulation and simplified methods for estimating the residual strength of a damaged double bottom. A typical double-bottom structure from a shuttle tanker was modelled. The structure was idealised to a small degree. Imperfections were introduced to the whole structure according to design rules. The most severe situation of the fully loaded condition was investigated. Hull girder bending was considered. Damage was caused by a variety of indenters that were specially designed to obtain a desired damage profile. A total of 16 numerical-calculation cases were investigated using the explicit commercial code LS-DYNA 971. A simplified method was derived. This method includes elastic plus rigid-plastic analyses of a 3-span, single-stiffener model. Unlike Smith's method, the present approach takes damaged stiffened panels into account in the residual strength assessment. The elastic and rigid-plastic analyses were combined to provide the load-end shortening curve for the damaged stiffeners. A simplified damage mechanism for the tripping of stiffeners is presented, as is a 3-span single stiffener model with proper boundary conditions. Both the analytical and single stiffener models were used to estimate the residual strength of a damaged double bottom. Both methods were validated with a non-linear, finite-element analysis (NLFEA) simulation carried out using LS-DYNA 971.

Residual strength assessment and destructive testing of decommissioned concrete bridge beams with corroded pretensioned reinforcement

Summary of nondestructive testing results compared with postfailure breakout Beam typeBeam labelVisual inspectionElectro potential mapping westElectro potential mapping eastPostfailure breakoutLongi-tudinal crack-ing visible on side of webMaxi-mum crack width west,* mmMaxi-mum crack width east,* mmMaxi-mum in failure zoneAverage over 0.5 m in failure zoneMaxi-mum in failure zoneAverage over 0.5 m in failure zonePeak load, kNNumber of corroded strands † Failure location from center-line, mDomi-nant failure mode12 pretensioned strands, no expansion joint 14G Neither 0 0 282 254 272 246 346 04.5 northShear 3C Neither 0 0 187 177 205 184 338 04.5 northShear 18E Both >2 >2 621 526 573 532 266 4 2 north Flexural 21F Both 2 3 577 526 494 449 260 31.5 southFlexural 3D Both 5 4 555 452 577 445 246 3.291.3 southFlexural 2C Both 3 3 572 442 509 430 233 41.4 southFlexural 12 pretensioned strands, expansion joint 13F Neither 0 0 189 177 174 163 317 0Reached maximum stroke 1D Neither 0 0 171 124 190 178 310 0 2 north Flexural

Assessment of residual ultimate strength of an asymmetrically damaged tanker considering rotational and translational shifts of neutral axis plane

This paper provides two convergence criteria to find translational and rotational locations of the neutral axis plane (NAP) for intact and damaged vessels. Definition of three types of asymmetries of a ship section is proposed: material-, load-, and geometry-induced asymmetries. Concept of moment plane (MP) is introduced to define the heeling angle of ship section. It is suggested that force equilibrium and force vector equilibrium criteria are simultaneously necessary to determine new position of NAP due to both translational and rotational shifts. In order to verify the applicability of the convergence criteria, midship section of a VLCC is selected with two types of asymmetries: one is due to heeling of a section and the other due to hull damages. 0° and 30° heeling conditions and collision-induced and grounding-induced damage extents based on ABS Guides and DNV Ship Rules are taken into account. The various section properties are compared according to the area reduction ratios for each heeling and damage cases. It is shown that ultimate hull girder capacities are closely related to the area reduction due to the damages. Using new convergence criterion, mobility of NAPs and force centroids in elastic and inelastic regimes are visually provided.

Residual strength of laminated composites after impact

This article deals with the residual strength assessment on completely as well as partially penetrated laminated composites due to impact loads by idealizing the damage locations as holes and cracks. Modifications are made in the inherent flaw model (IFM) of Waddoups, Eisenman, and Kaminski (known as the WEK model) to correlate the fracture data of laminated composites. For velocities above complete penetration, the residual strength is identical to the static strength of the laminated composite with a hole having the same diameter as the impacting particle. For this case, the inherent flaw length ahead of the notch is correlated with notched and un-notched strengths through fracture parameters. For the case where the impact velocities are less than the penetration velocity, an empirical relation is proposed following the IFM for the residual strength in terms of kinetic energy of the impact. The adequacy of the modified IFM is demonstrated through comparison of fracture analysis results with tensile, compressive, and impact fracture strength of laminated composites containing holes and cracks.

Assessment of Residual Tensile Strength of Carbon/Epoxy Composites Subjected to Low-Energy Impact

This paper presents the results of an experimental study to investigate the effects of impact loading on the residual tensile strength of woven graphite epoxy laminates with a toughened resin system. In this study, both cross-ply, [0∕90]6, and angle-ply, [±45]6, laminate lay-up configurations were studied and compared. Test specimens were subjected to various levels of impact loading, after which tensile pull tests were performed to determine the residual tensile strength properties. The study results demonstrated that impact damage causes a significant reduction in tensile strength properties of woven cross-ply [0°/90°] laminates. For example, cross-ply laminated composite specimens subjected to the lowest impact level, 6.8J, exhibited a 25% decrease in ultimate tensile strength. Angle-ply woven laminates [±45°], however, exhibited an 18% increase in ultimate tensile strength after being subjected to 6.8(J) impact. This characteristic of increasing tensile strength in [±45°] specimens is an example of increased fiber reorientation in composite laminates with limited fiber damage.