scholarly journals Analysis of the influence of residual stresses on possible defects formed during production of carbon-epoxy composites

2020 ◽  
pp. 59-68
Author(s):  
Дарья Александровна Бондарчук ◽  
Борис Никитович Федулов ◽  
Евгений Викторович Ломакин
Keyword(s):  
Residual Stresses ◽  
Epoxy Composite ◽  
Free Edge ◽  
Defect Zone ◽  
User Subroutine ◽  
Stress Components ◽  
Energy Release Rates ◽  
History Of ◽  
Strain Stress ◽  
Residual Stresses And Strains

В настоящей работе изучено влияние наличия остаточных напряжений в образце углерод-эпоксидного композита, сформировавшихся в процессе его производства, на такие возможные дефекты как межслоевое расслоение. Исследование посвящено анализу НДС в регулярных образцах вблизи зоны дефекта в течение цикла отверждения, а также при образовании свободного края в материале после разреза в зависимости от длины трещины. Для моделирования процесса отверждения решалась связанная тепловая и прочностная задача в условиях плоской деформации. Для описания поведения композитного материала в процессе производства, включая процессы формования, полимеризации, развития остаточных напряжений и деформаций, была разработана и реализована специальная пользовательская подпрограмма для ПО ABAQUS. В частности, в данной работе была проанализирована история величин скоростей энерговыделения в режимах раскрытия трещины по механизму нормального отрыва и поперечного сдвига в процессе полимеризации и последующего разрезания с образованием свободного края. Обнаружен незначительный рост значений GI , GII в вершине трещины в процессе полимеризации и многократное превышение этих значений после механического среза. В результате численного моделирования выявлено, что остаточные напряжения не оказывают существенного влияния на рост дефекта в композите на этапе его изготовления, но при приложении дальнейшей нагрузки на образец могут способствовать интенсивному росту расслоения. In the present study, the effect of presence of residual stresses inherited during manufacturing on delamination defect in carbon-epoxy composite specimen is investigated. The research is devoted to understanding of strain-stress state in regular specimens near defect zone during cure cycle and after free edge cut depending on crack length. To describe the behavior of the composite material during manufacturing process- including processes of formation, polymerization, development of residual stresses and strains, the special user subroutine was developed and implemented in ABAQUS FEM software. The history of energy release rates under mode I, II ( GIc , GIIc) where analyzed over time during process of polymerization and free edge cut. A slight increase in the GI and GII values at the crack tip during polymerization and a multiple excess of these values after a mechanical cut is shown. Obtained by modelling values for stress components are essential and cannot be ignored in consequent structural analysis. The results of the study can be applied for prediction of residual stresses in composite structure by means of simulation and further understanding the nature of fracture of composites.

Fundamentals of Residual Stresses in Joints Between Dissimilar Materials

MRS Bulletin ◽  
1995 ◽  
Vol 20 (1) ◽  
pp. 37-39 ◽  
Author(s):  
B.H. Rabin ◽  
R.L. Williamson ◽  
S. Suresh
Keyword(s):  
Residual Stresses ◽  
Material Properties ◽  
Critical Stress ◽  
Failure Mechanisms ◽  
Dissimilar Materials ◽  
Free Edge ◽  
Structural Components ◽  
Failure Characteristics ◽  
Stress Components ◽  
Metal Joint

When a discontinuity in material properties exists across a bonded interface, stresses are generated as a result of any thermal or mechanical loading. These stresses significantly affect strength and failure characteristics and may be large enough to prevent successful fabrication of a reliable joint. The use of an interlayer material to successfully reduce mismatch stresses, thereby preventing joint failure or improving joint strength and reliability, requires knowledge of failure mechanisms and of the effects of interlayer properties on the critical stress components.The origin of residual stresses developed during cooling of a ceramic-metal joint from an elevated fabrication temperature is illustrated qualitatively in Figure 1. Away from edges, the in-plane (parallel to interface) stresses are typically compressive in the ceramic and tensile in the metal. These stresses can cause cracking perpendicular to the interface, leading to spalling or delamination failures. Such failures are frequently observed in thin-film and coating geometries. Where the interface intersects a free edge, large shear and axial (perpendicular to the interface) stresses are generated. The edge stresses are typically tensile within the ceramic and tend to promote crack propagation within the ceramic parallel and adjacent to the interface. This is the most commonly observed failure mode in bonded structural components.

scholarly journals Modeling and Calculating of Residual Stress and Strain of Butt Welded Joint

2021 ◽  
Vol 31 (5) ◽  
pp. 58-67
Keyword(s):  
Finite Element Method ◽  
Residual Stress ◽  
Finite Element ◽  
Residual Stresses ◽  
Welded Joint ◽  
The Finite Element Method ◽  
Force Method ◽  
Stress Components ◽  
Residual Stresses And Strains ◽  
Element Method

The non-uniform thermal expansion and contraction resulting from welding processes cause residual stresses and strains. Experimental studies on measuring welding residual stresses and strains of structure are costly and sometimes they are not possible. Previously, analytical methods with idealized models were developed to determine the welding residual stresses and strain. Recently, numerical methods are constructed to analyze the stresses and the strains in welded structures. This paper presents the calculation results of residual stress and welding strain in butt welded joint of S355J2G3 carbon steel of 5 mm thickness made by MAG welding process with a single pass. The calculation is performed by two methods: the imaginary force method and the finite element method. In the finite element method, the SYSWELD software is used to simulate and to determine residual stresses and strain of this welded joint. The results of finite element method are compared with those of imaginary force method to show the rationality and the advantages of finite element method. The study results have shown that in this welded joint, only the longitudinal and transverse stress components are important and the other stress components are negligible.

Fatigue Damage Accumulation under the Complex Varying Loading

2014 ◽  
Vol 617 ◽  
pp. 187-192 ◽  
Author(s):  
Boris Melnikov ◽  
Artem Semenov
Keyword(s):  
Damage Accumulation ◽  
Low Cycle Fatigue ◽  
Damage Model ◽  
Hysteresis Loops ◽  
Fatigue Analysis ◽  
Wave Loads ◽  
Fatigue Damage Accumulation ◽  
History Of ◽  
Strain Stress ◽  
Irregular Loading

Fatigue analysis of steel parts of structures, which are subjected to complex irregular loading programs caused by wind, thermal, wave loads, earthquakes and combined imposed actions, requires in some cases using special methods of stress-strain evaluation. The model of the low cycle fatigue nonlinear damage accumulation is developed with taking into account the history of the deformation process. The damage is defined on the base of considering the quasi-static accumulation of maximal strain (stress) and hysteresis loops. The identification of material constants of the model is discussed. Application of the damage model for fatigue analysis of the antennas, pipelines, basements and fasteners units is considered and a comparison with experiments is given.

Loading and Heating of a Simple Structure with Linear Work Hardening

1963 ◽  
Vol 67 (626) ◽  
pp. 92-102 ◽  
Author(s):  
E. H. Mansfield
Keyword(s):  
Residual Stresses ◽  
Work Hardening ◽  
Heat Load ◽  
Simple Structure ◽  
Tangent Modulus ◽  
Plastic Range ◽  
Repeated Applications ◽  
Residual Stresses And Strains

Summary:An analysis is made of the stresses and strains in a loaded two-bar tie when one of the bars is subjected to heating. The material of the bars is assumed to possess linear work hardening characteristics, i.e. a constant tangent modulus in the plastic range, and these characteristics are assumed to be independent of temperature. The following cycles of loading and heating are considered: load-heat-cool-unload, load-heat-unload-cool, heat-load-unload-cool, heat-load-cool-unload, and it is shown how, and when, these cycles produce differing stresses and strains and, in particular, differing residual stresses and strains. The effect of repeated applications of these cycles, when incremental shake-down may occur, is also considered.

Residual stresses and strains in molded plastics

1952 ◽  
Vol 7 (3) ◽  
pp. 244-252 ◽  
Author(s):  
W.H Markwood ◽  
H.M Spurlin
Keyword(s):  
Residual Stresses ◽  
Residual Stresses And Strains

A Limiting Defect Study of an Elbow

2011 ◽  
Author(s):  
Jinhua Shi ◽  
David Blythe
Keyword(s):  
Residual Stress ◽  
Residual Stresses ◽  
Hoop Stress ◽  
Defect Size ◽  
Welding Residual Stress ◽  
Central Section ◽  
Butt Welding ◽  
Wide Range ◽  
Stress Components ◽  
Hoop Stresses

In order to ensure the integrity of a seamless butt-welding elbow, both the central section and ends of the elbow need to be assessed, as the maximum stress is normally located at the central section of the elbow but there are no welding residual stresses. Furthermore, at the ends (welds) of the elbow, very high welding residual stresses exist if the welds have not been post weld heat treated but the primary stresses induced by the internal pressure and system moments are lower. For a 90 degree elbow welded to seamless straight pipe, both maximum axial and hoop stress components in the elbow can be calculated using ASME III NB-3685. At the ends of the elbow, axial and hoop stress components can be obtained using the stress equations presented in the paper of PVP2010-25055. In this paper, a series of limiting defect assessments have been carried out on an elbow assuming a postulated axial external defect as follows: • A number of assessments have been conducted directly using the axial and hoop stresses calculated based on ASME III NB-3685 for different system moments. • A series of assessments have been carried out using the axial and hoop stresses calculated using the stress equations presented in the paper of PVP2010-25055, a wide range of welding residual stresses and different system moments. A comparison of the assessment results in the elbow and at the ends of the elbow shows that when system moments are relatively low and the welding residual stress is high, the limiting defect size is located at the ends of the elbow; when the system moments are high and the welding residual stress is low the limiting defect size is located at the central section of the elbow. Therefore, it can be concluded that when assessing an elbow, the assessments should be carried out at both the central section and the ends of the elbow, in order to ensure the integrity of the elbow.

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