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Mechanical properties of solids
Published in Marios Soutsos, Peter Domone, Construction Materials, 2017
Cyclic loading is very common, for example, wind and wave loading, vehicle loading on roads and bridges. We can define the characteristics of the loading as shown in Figure 2.18, in which p = period of loading, ∴ frequency = 1/p (e.g. in cycles/s or Hertz)σmax = maximum applied stress and σmin = minimum applied stressσm = mean stress = (σmax + σmin)/2S = stress range = (σmax − σmin)
Influence of airfield pavement roughness and ponding on gear life and safety of commercial aircraft
Published in Andreas Loizos, Imad L. Al-Qadi, A. (Tom) Scarpas, Bearing Capacity of Roads, Railways and Airfields, 2017
Solid materials when subjected to repeated cyclic load may exhibit structural damage by the fatigue mechanism. The fatigue failure happens due to the repetitions of large numbers of cycles of load. Fatigue manifests in the form of initiation of a crack followed by its growth until the critical crack size of the parent material under the repeated operating load is reached, which leads to crack and rupture. In general, the MLG are affected by two kinds of vibrations: (1) transient vibrations, which originate from the bumps, potholes, and rutting or depressions in the runway or unexpected changes in case of braking action and (2) continuous self-sustaining vibrations associated with a roughness wavelength with very high amplitude, which can initiate early MLG fatigue failure. Therefore, longitudinal roughness and other pavement distresses and irregularities play important roles on the structural performance and life of an aircraft’s main landing gear system.
Damage Mechanics for Static and Fatigue Applications
Published in Raul D.S.G. Campilho, Strength Prediction of Adhesively-Bonded Joints, 2017
Ian A. Ashcroft, Aamir Mubashar
Fatigue is the failure of a structure under a repetitive or cyclic loading regime in which the loads involved are considerably lower than those involved in instantaneous, or quasi- static, failure. Long periods can be spent in an initiation phase of fatigue damage, in which there may be no outward signs of damage. Fatigue damage can be initiated or accelerated by many factors, such as accidental impact, over-loading, corrosion, abrasion etc. and failure can occur rapidly in the final stages. The long time durations, effect of external and internal factors and stochastic nature of fatigue failure makes it difficult to predict accurately. Hence, it is very difficult to design against fatigue failure without resorting to large safety factors, and thus incurring structural inefficiencies. Monitoring fatigue damage can also be difficult, particularly if initiation is in an inaccessible location or if the critical crack size before rapid fracture is very small. However, progressive damage models can help in predicting the sequence of events leading to failure and the associated effects that could be used in structural health monitoring, e.g. changes in stiffness or modal response.
Enhancing shear behaviour of the exterior beam-column joint using sufficient reinforcement details or ultra-high-performance fiber-reinforced concrete
Published in European Journal of Environmental and Civil Engineering, 2023
Sayed Ahmed, Heba A. Mohamed, Talaat Ryad, Ayman Abdo
BCJ samples were placed on the test device to enable testing. The displacement measuring device was placed at the free end of the top, and the loading device was placed below the free end of the beam (Figure 5). This setup provides suitable boundary conditions for BCJ as in practice. The specimen’s column is loaded with a constant axial load of 100 kN to match the dead and live loads of the prototype structure. A servo-controlled hydraulic jack is applied to simulate a gravitational load from the upper floors. Then a 350 kN actuator is used to apply cyclic loading at the beam’s free end in the displacement control mode. The cyclic load pattern used in this study is one-way at the end of the beam (Ahmed et al., 2019). A cyclic load consists of repeated loading and unloading cycles (the load returns to zero), as shown in Figure 6c. The actuator applied each target displacement in a semi-constant and monotonous position (5 kN, 10 kN, 15 kN, ……) until sample collapse occurred. The LVDT was attached to the beam’s free end to measure the deflection, as shown in Figure 5a-65.
Assessment of remaining fatigue life based on temperature-evolution measurements
Published in Nondestructive Testing and Evaluation, 2022
Atsushi Akai, Yuka Kojima, Yasumoto Sato
Engineering structures and components are often subjected to cyclic loading, which ultimately leads to fatigue failures. Under time, cost and labour constraints, engineering structures and components are inevitably worked out until their effective performance limits are reached. To guarantee the long-term use of engineering structures and components, their remaining fatigue lives must be assessed. Since a part of the energy imparted to a material under cyclic loading above the fatigue limit (fatigue loading) dissipates in the form of heat, fatigue loading increases the material temperature. In the recent studies pertaining to thermography-based techniques, the fatigue behaviour has been investigated in terms of the energy dissipation derived from temperature signals measured using infrared thermography. The corresponding energy dissipation component was obtained using several approaches, such as lock-in thermography [1–6], calorimetric analysis [7,8], specific heat loss [6,9,10] and thermoelastic phase analysis (TPA) [3,11].
A comparative study on hybrid fatigue stress-life model of RC beams strengthened with NSM CFRP
Published in Mechanics Based Design of Structures and Machines, 2022
Fatigue is an accumulative process of minor damages to a material followed by a sudden failure due to cyclic loading. The structural components of bridges are frequently subjected to repetitive application of traffic loads. A 40-years old Class-A highway bridge might experience no less than 58 × 108 cycles of traffic loading over its design service life (Heffernan 1997); even at stresses below the yield strength of the used material, this might result in cyclic stresses that lead to physical microscopic damage. As load cycles continue, microscopic damage builds up until it becomes a crack (Dowling 2007). Once these minor cracks combine into a major crack, the cross-sectional area of the structural member will be essentially decreased. Over time, the cumulative damage can lead to a sudden failure when the applied load causes stress higher than what the cross-sectional area can withstand (Sobieck, Atadero, and Mahmoud 2015). Fatigue failures are dangerous because they occur without any warning.