scholarly journals Effect of the Cyclic Crack Opening-Closure during Epoxy-Curing Period of a CFRP Strengthening System Bonded on Concrete Substrate

2022 ◽  
Vol 3 (1) ◽  
pp. 88-102
Author(s):  
Marc Quiertant ◽  
Claude Boulay ◽  
Laurent Siegert ◽  
Christian Tourneur
Keyword(s):  
Fatigue Test ◽  
Cyclic Load ◽  
Crack Opening ◽  
Experimental Studies ◽  
Control Sample ◽  
Fatigue Loading ◽  
Curing Period ◽  
Rc Structure ◽  
Epoxy Curing ◽  
Cracked Specimens

This article investigates the potential detrimental effects of cyclic load during the installation of externally bonded (EB) carbon fiber-reinforced polymer (CFRP) on a damaged reinforced concrete (RC) structure. Four RC specimens were tested in three point bending to study the consequences of crack cyclic opening-closure during epoxy-curing period. A first RC specimen (without bonded CFRP) was loaded monotonically up to failure to serve as undamaged control sample. The three other specimens were pre-cracked before being subjected to a fatigue loading procedure to simulate service condition of a damaged RC structure. Two of the three pre-cracked specimens were strengthened by EB CFRP. One specimen was repaired before the fatigue test while the other one was repaired during the fatigue test. Finally, remaining capacities of all three pre-cracked specimens were measured through monotonic bending tests until failure. It was found that, although bonding of CFRP reinforcement during cyclic load can induce some interesting features with regard to serviceability, cyclic crack opening and closing alters the cure process of epoxy located below the initial crack and decreases the effectiveness of the strengthening at ultimate state. Extended experimental studies are then needed to assess reliable safety factor for the design of repairing operations in which the bridge has to be maintained in service during CFRP installation.

scholarly journals Full Scale Fatigue Test and Failure Analysis of Advanced Jet Trainer Wing

2018 ◽  
Vol 188 ◽  
pp. 04023
Author(s):  
Vaclav Horak ◽  
David Novotny
Keyword(s):  
Fatigue Life ◽  
Fatigue Test ◽  
Current Method ◽  
Fatigue Loading ◽  
Eddy Current Method ◽  
Verification Method ◽  
Fuel Tanks ◽  
Strain Data ◽  
Non Destructive ◽  
Test Control

A verification method for the fatigue life of the jet trainer wing with integrated fuel tanks is presented. The test was performed to identify the critical points of the structure, to determine strain data and to proof fatigue life of the wing. During the test the non-destructive inspection methods for the identification and evaluation of the critical failures were employed; i.e. visual, ultrasonic and eddy current method. The failures were classified according to significance and reparability. The special test rig was designed to redistribute the load on the structure and to determine test data. The load control system MTS AeroSTTM was used for fatigue test control. The fatigue load sequences with multilevel profiles of static and fatigue loading were applied. During the test, more than 230 failures were identified. The critical failures were repaired when found using two types of repair (metal and composite). The repairs were monitored during subsequent fatigue test run and evaluated to utilize in service.

High Temperature Fatigue Assessment of a SiCf/SiC Ceramic Matrix Composite Using Advanced Monitoring Techniques

2019 ◽  
Author(s):  
Christopher D. Newton ◽  
Steven P. Jordan ◽  
Martin R. Bache ◽  
Louise Gale
Keyword(s):  
Silicon Carbide ◽  
Crack Opening ◽  
Ceramic Matrix Composite ◽  
Fatigue Loading ◽  
Cyclic Stress ◽  
Image Correlation ◽  
Material System ◽  
Damage Initiation ◽  
Macro Scale ◽  
Stress States

Abstract Laboratory based experiments to assess the “damage tolerance” of any new material system are a pre-requisite to engineering design, especially for aerospace components. In the case of CMCs, macro-scale specimens are preferred containing representative fibre-matrix architectures that support the definition of mechanical properties under service representative stress states. The combination of complex internal structure and inevitable processing artefacts within CMCs provides numerous sites for damage initiation. Damage then progresses in an inhomogeneous manner prior to ultimate failure at some critical location. Traditional techniques employed for strain measurement (extensometry/strain gauges) prove to be ineffective tools when testing these advanced composites. More complex characterization is essential in order to assess the localised response of the material. Advanced techniques, specifically digital image correlation and acoustic emission, have been applied to the evaluation of an CVI/MI silicon carbide reinforced/silicon carbide CMC tested at the elevated temperature of 800°C under fatigue loading. The spatial and temporal indications of damage were correlated to the observable forms of damage initiation and progression. Ancillary use of an in-situ SEM loading stage provided insight into the crack opening and closing mechanisms active within this material when under cyclic stress.

Effects of environmental conditions on the axial tension–compression fatigue behavior of carbon/epoxy plain-weave laminates containing flaws

2020 ◽  
Vol 54 (27) ◽  
pp. 4215-4230
Author(s):  
Marc-Claudel Deluy ◽  
Mohamed Khay ◽  
Anh Dung Ngo ◽  
Martine Dubé ◽  
Rajamohan Ganesan
Keyword(s):  
Fatigue Life ◽  
Environmental Conditions ◽  
Cyclic Load ◽  
Fatigue Testing ◽  
Fatigue Behavior ◽  
Real Life ◽  
Compressive Load ◽  
Fatigue Loading ◽  
Plain Weave ◽  
Strain Increase

The objective of this work is to investigate the effects of environmental conditions on the axial fatigue behavior of a carbon/epoxy plain-weave laminate with an embedded flaw subjected to a partially reversed cyclic load (stress ratio R = −0.1) in tension–compression. This specific material is more commonly used in aerospace engineering for the manufacturing of aircraft structural parts, which are directly exposed to various environmental conditions during service. Specific environmental and loading conditions that are appropriate to simulate real-life conditions are considered to observe and collect information about the material's behavior. For the investigation, dry and wet coupons were submitted to room temperature, 82 and 121 ℃ under loading frequencies of 7 and 15 Hz. A maximum allowable strain increase criterion is used to monitor the flaw growth threshold or delamination onset, during fatigue testing. The ultrasonic imaging (C-scan) technique is used to verify and confirm the delamination onset. Results show that the delamination onset strain increase criterion, along with fatigue life, generally decreased as the operating temperature and humidity were increased and that frequency had little effect on the delamination onset fatigue life. The S– N curves obtained from the tension–compression fatigue data were then compared to those of a previous work carried out in tension–tension fatigue loading. Results show a clear degradation in the delamination onset fatigue life of the coupons tested under tension–tension cyclic loading when the minimum tensile component of the cyclic load was replaced with a compressive load of the same magnitude.

ACOUSTIC EMISSION BEHAVIOUR OF OVER-REINFORCED CONCRETE BEAMS

2019 ◽  
pp. 4-12 ◽  
Author(s):  
V. V. Bardakov ◽  
A. I. Sagaydak ◽  
S. V. Elizarov
Keyword(s):  
Acoustic Emission ◽  
Reinforced Concrete ◽  
Cyclic Load ◽  
Concrete Beams ◽  
Experimental Studies ◽  
Reinforced Concrete Beams ◽  
Emission Data ◽  
Point Bend ◽  
Destructive Processes ◽  
The Relationship

The paper presents the results of the conducted experimental studies on three-point bend testing of over-reinforced concrete beams with incremental cyclic load, up to destruction, using the acoustic emission method. In total 3 RC beams differ from each other in reinforcement type, concrete composition and ultimate load were tested. Special attention is paid to the investigation of the relationship between destructive processes occurring during the testing of reinforced concrete beams and the evolution of acoustic emission data registered during the test. The analysis described in the article makes it possible, on the basis of acoustic emission data, recorded during the tests, to distinguish the stages corresponding to the different technical state of over-reinforced concrete structures.

Experimental Evaluation of Corrosion Effect on Bond Between Steel and Concrete in Presence of Cyclic Action

2009 ◽  
Vol 417-418 ◽  
pp. 345-348 ◽  
Author(s):  
Luca Giordano ◽  
Giuseppe Mancini ◽  
Francesco Tondolo
Keyword(s):  
Reinforced Concrete ◽  
Cyclic Load ◽  
Crack Opening ◽  
Concrete Structures ◽  
Electrochemical Corrosion ◽  
Reinforced Concrete Structures ◽  
Reinforcing Bars ◽  
Cyclic Action ◽  
In Series ◽  
Ultimate Condition

Corrosion modifies the steel-concrete interface in reinforced concrete structures. The efficiency of the connection between the two materials is reduced and the structural behavior both in service and in ultimate condition is affected. Moreover in structures subjected to cyclic load, a simultaneous mechanical deterioration due to the load is present. In this work an experimental analysis on reinforced concrete structures under both cyclic load and corrosion of reinforcing bars is presented. Three couples of reinforced concrete ties are connected in series and subjected to the same stress variation in order to produce the cracking conditions and to activate the bond mechanism. However, while one of the two reinforced concrete ties is only subjected to cyclic load, the second one is also corroded using an accelerated electrochemical corrosion process. The simultaneous effect of the cyclic load and corrosion is evaluated monitoring the crack opening on the structures during the test and by means of visual inspection of the sample. The test results show the correlation between the mechanism of bond and the average level of stresses for an amplified stress range.

STRUCTURAL FEATURES OF DAMAGES ACCUMULATION IN CONDITIONS OF COMBINED CYCLIC LOADING

2019 ◽  
Vol 85 (5) ◽  
pp. 46-51 ◽  
Author(s):  
L. L. Smirnova ◽  
A. V. Zinin
Keyword(s):  
Elastoplastic Deformation ◽  
Structural Changes ◽  
Experimental Studies ◽  
Fatigue Loading ◽  
Structural Features ◽  
Subsequent Stage ◽  
Preliminary Loading ◽  
Second Stage ◽  
Fatigue Durability ◽  
Damage To The Material

A significant part of the elements of machines and structures along with stationary fatigue is subjected to combined impacts of low-cycle and multi-cycle fatigue loading in operation. The physical nature of their fracture in these conditions depends on the ratio of the mode parameters and entails the necessity of advanced research. The predominance of this or that process determines the nature of the damage accumulation which leads to the destruction. Under such conditions, i.e., preliminary cyclic elastoplastic deformation followed by subsequent fatigue loading, the material subjected to preliminary loading at the first stage can be considered the "new material" with the new properties acquired upon cyclic elastoplastic loading which then undergoes further fatigue loading at the second stage. Hence, at the second stage, the new properties of the material are determined by the level of structural changes and damages earlier accumulated in the material. In this case, the damage to the material is considered on the basis of the well-known statement about the staging character of plastic flow, two main processes, i.e., shear, caused by the interaction of dislocations, and destructuring, attributed to violation of the continuity or integrity of the metal. Experimental studies of changes in the durability of cyclically hardened and cyclically softened steel specimens at different levels of preliminary elastoplastic deformation with varying number of cycles and amplitudes of preliminary elastoplastic strain showed the occurrence of an additional damage to the material when combination of loading modes leads to change in the fatigue durability at the subsequent stage of the basic multi-cycle loading. It is shown that correlation between changes in the fatigue durability and structural state of the material, caused by accumulated damage upon preliminary overloads, and, moreover, those changes can be characterized by the ratio of plastic and destructive strains as a Q-factor of the material.

Crack Width Evolution of R/C Structures Subject to Corrosion and Fatigue

2010 ◽  
Vol 452-453 ◽  
pp. 417-420
Author(s):  
Luca Giordano ◽  
Francesco Tondolo
Keyword(s):  
Reinforced Concrete ◽  
Service Life ◽  
Crack Width ◽  
Cyclic Load ◽  
Crack Opening ◽  
Reinforced Concrete Structures ◽  
Chemical Attack ◽  
Experimental Campaign ◽  
Simultaneous Loading ◽  
Concrete Interface

Corrosion modifies the steel-concrete interface in reinforced concrete structures. Moreover in structures subjected to cyclic load, a simultaneous mechanical deterioration due to the load is present. Both phenomena can lead to an evolution of cracks width during the service life. In order to evaluate the crack openings increase, an experimental campaign on reinforced concrete ties subjected to simultaneous loading and corrosion have been realized. Transversal crack opening, initially due to loading and longitudinal corrosion cracks evolution is monitored. Results highlight the differences in terms of corroded and uncorroded specimens, static and cycling test and also different loading amplitude. Finally it can be observed as the growing of the damage is significantly different when a cycling action, combined with a chemical attack is present.

ENSURING TIGHTNESS IN PRESSURE COUPLING PARTS

2021 ◽  
Vol 2021 (11) ◽  
pp. 51-59
Author(s):  
Nikolay Kurnosov ◽  
Aleksandr Tarnopol'skiy ◽  
Yuliya Nakashidze
Keyword(s):  
Mechanical Properties ◽  
Cyclic Load ◽  
Experimental Studies ◽  
Physical And Mechanical Properties ◽  
Accelerated Testing ◽  
Dynamic Loads ◽  
Surface Material ◽  
Urgent Problem ◽  
Mating Surface ◽  
The Impact

Work objective is to solve the urgent problem of increasing the tightness and reliability of pressure couplings during their operation under dynamic loads. Theoretical and experimental studies assessing the impact on the tightness due to roughness nature of mating surfaces and three types of coatings: soft, double-layer and hard have been undertaken. The joints were tested under the influence of axial cyclic load and torque on a bench for accelerated testing. It is established that tightness of pressure couplings during operation under dynamic loads significantly depends on the parameters of microgeometry and physical and mechanical properties of the mating surface material that determine their actual contact area. Recommendations for preparing the surfaces of parts before pressure coupling assembling have been developed. It is proved that the use of regular microrelief and soft galvanic coatings of mating surfaces have a significant effect on the tightness of pressure couplings.

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