An Acoustic Emission Method for Assessing the Degree of Degradation of Mechanical Properties and Residual Life of Metal Structures under Complex Dynamic Deformation Stresses

An acoustic emission method for assessing the degree of degradation of mechanical properties under conditions of complex dynamic deformation stresses is proposed. It has been shown that changing the operating conditions of metal structures, peak loads, external collisions, and thermally changing loads, which cannot be taken into account, leads to uncertainty and unpredictable structural changes in the material. This in turn makes it difficult to identify the state of the structure material to ensure trouble-free operation of the equipment. Changes in the mechanical properties under difficult loading conditions are identified by polynomial approximation of the results of AE measurements and the construction of boundary curves separating the operability region from the fracture region. This is achieved by approximating the experimental dependences of the acoustic parameters for various types of loading. This approach significantly expands the capabilities of the technical means of identification systems of metal structures, and in particular, allows the current state of the equipment and its suitability for further operation to be assessed without stopping the equipment in real time. It is of interest not only to fix the damage, but also to diagnose the processes of reducing the mechanical properties during the operation of the equipment.

Fatigue analysis of a composite ring: Experimental and theoretical investigations

The behavior of composite rings against fatigue loading is analyzed. Experimental study is performed to evaluate the ultimate hoop strength of the composite ring as a requirement before fatigue testing. Then, fatigue tests are performed at three different load levels. Afterward, progressive damage modeling in the context of continuum damage mechanics is utilized to theoretically estimate fatigue lifetimes of the investigated rings. The modeling consists of three parts as stress analysis, damage estimation and degradation of mechanical properties. It is mainly aimed to reduce the required runtime for the accomplishment of fatigue analysis while the accuracy is at least compromised. Therefore, a manual technique is adapted for extracting stress components on the ring. Degradation of mechanical properties takes place either through gradual procedure or sets of sudden laws. The gradual degradation of mechanical properties is performed based on the damage progression as a function of cycle numbers and stress state. Sudden degradation is done after occurrence of failure. After reduction of mechanical properties, the model is updated and whole procedure repeats till the whole layers fail. Finally, the results of fatigue modeling are compared with performed experimental study and a very good agreement is observed.

Degradation and Damage of Composite Materials in Marine Environment

IIn spite the fact that composite materials have been in use in the maritime sector for over a half of century, classification societies regulations tend to limit the usage of composites at the larger scale. One of the reasons for such strict class rules is a lack of comprehensive analytical and numerical models representing the behaviour of composites in the sea environment. Understanding the process of degradation and damage of composite materials assisted by sea environment a crucial step in building such a model. This paper aims to give a critical review of the research advancements in assessments of the sea environment influence on the degradation of mechanical properties of composites with a special emphasis on developed models of processes containing water and moisture entering composite inner structure. The list of major references in the last five years is given and suggestions for future research are discussed.