Damage Initiation in Unidirectional Polymeric Composites with Manufacturing Induced Irregularities

In this work, the initiation of the first failure event in unidirectional polymer composites subjected to different loading conditions is studied. Two energy based point failure criteria – critical dilatational and critical distortional energy densities – are considered. Local stress fields are calculated by finite element models using micromechanical simulations to evaluate damage initiation in the matrix by a brittle failure mechanism (cavitation) and by an inelastic (yielding) process. The disorder in the fiber distribution induced by manufacturing is quantified by defining the degree of nonuniformity (NU) of fiber distribution in the composite cross section. An algorithm to create simulations of the nonuniform distribution of fibers at different overall fiber volume fractions (FVFs) and different degrees of nonuniformity is developed. Representative volume elements (RVEs), with their minimum size determined on the basis of statistical analysis of interfiber distances are established for different fiber volume fractions. Under tension applied normal to the fibers, brittle cavitation is found to occur before yielding in the matrix. This first failure event is assumed to induce local debonding of the fiber/matrix interface. Effects of variables such as the degree of nonuniformity and the fiber volume fraction, as well as the ratio of matrix to fiber stiffness modulus, on the initiation of brittle cavitation are studied. Combined loading consisting of transverse tension and axial shear applied to unidirectional composites is studied next. It is found that under certain axial shear/transverse tensile stress ratios brittle cavitation requirements are fulfilled. When only axial shear is imposed, cavitation requirements are not satisfied. Instead, matrix yielding is found to occur. A parametric study of the matrix/fiber stiffness ratio shows that the mechanical strain to onset of cavitation under transverse tension increases as this ratio increases and approaches a constant value at high ratios under given fiber volume fractions and degree of nonuniformity. Also, under these conditions and under axial shear, the mechanical strain at which yielding initiates is found to increase with increasing the matrix/fiber stiffness ratio. A limited study of the effects of matrix voids was also conducted and the preliminary results showed that the presence of voids affects the initiation of brittle cavitation by altering the local stress fields near the fiber/matrix interfaces

A Hybrid Analytical-Numerical Model of Heat Generation and Distribution in Friction Stir Welded AA2024 Butt Joints

Being a solid-state process, friction stir welding (FSW) is considered a candidate technique for welding critically-microstructure-sensitive materials such as heat-treatable aluminum alloys. A hybrid computational model that employs both analytical and numerical approaches was used to estimate the amount of heat generated in the FSW of AA2024-T4 butt-welded sheets and how it is distributed as a function of time using a 3D transient heat transfer finite element analysis (FEA). Experimental procedures were used to validate the heat distribution in the welded butt joints using candidate rotational and travel speeds from the numerical model. The model outcomes show that rotational speed less than 600 rpm gives insufficient heat input when the optimum travel speed is 25 mm/min while higher rpm would cause overheating and flash formation. Structural and mechanical joint characterizations were performed to ensure the validity of the optimized process parameters. The model recommended parameters give the defect-free butt joints with the best efficiency in terms of ultimate strength. The Vickers hardness profile (W-shaped) for the welds’ cross-sections shows that 600 rpm gives the highest values in all different weld zones compared to that welded at 400 and 800 rpm

تحقيق معايير الاستدامة الاجتماعية لمسارات المشاة داخل مرکز المدينة "دراسه حاله (شارع الحسينـي البحري بمدينة المنيا ) " Criteria for Achieving Social Sustainability for pedestrian paths in the city center Case study :Al-Hussein El Bahari Street in Minya city

The human being is the real wealth of any society, and it is the main goal of sustainability. It is the creation of an appropriate environment that enables people and seeks to invest their abilities, rehabilitate them and create an opportunity for creativity, which makes them able to participate effectively in society. This research discusses pedestrian paths because of their great importance as an urban element within the city centre, where pedestrian paths play an important social role in the urban environment, thus clarifying the importance of achieving social sustainability for path users, whether residents or visitors in cities, and it can be achieved by studying the pedestrian’s human need and their money from Impact on the quality of the tracks. It aims Research to restore the role of pedestrian paths to achieve standards of social sustainability and its impact on the spatial structure of the city, and the research proposes a set of standards that achieve social sustainability for pedestrian paths within the city centre and restore the functional and social role of pedestrian paths, then study these proposed standards on the applied case: Al-Husseini Al-Bahari Street in the governorate Minya. The research was divided into three axes, the first axis clarifying the concept of social sustainability in the built environment. The second axis: Designing the general framework for indicators and mechanisms to achieve social sustainability for pedestrian paths, and for the purpose of testing the hypothesis, the indicators of the theoretical framework were applied to a case study (Al-Husseini Al-Bahari Street in Minya Governorate), in order to research a framework for achieving social sustainability and activating them for pedestrian paths, within the third axis (the applied study) and analyse the results of the application.   يناقش هذا البحث مسارات المشاة لما لها من أهمية بالغة کعنصرعمراني داخل مرکز المدينة, حيث تؤدي مسارات المشاة دوراً اجتماعياً هاماً في البيئة العمرانية ,فقضايا التفاعل بين الإنسان والعمران والتأثير المتبادل بينهم أصبحت من أهم القضايا العمرانية ,وبذلک يظهر أهمية تحقيق الاستدامة الاجتماعية لمستخدمي المسار سواء من السکان أوالزوار في المدن، ويتم ذلک عن طريق دراسة السلوک والاحتياجات الانسانية للمشاة ومالها من تأثير علي مستوي الاستدامة الاجتماعية للمسارات. لقد تضائل دور مسارات المشاة داخل مراکز المدن منذ بداية الثورة الصناعية في استيعاب الأنشطة والإحتياجات المختلفة للمستخدمين وذلک للاهتمام بالمتطلبات والاحتياجات المادية الخاصة بحرکة السيارات, لذلک يهدف البحث لاستعادة دور مسارات المشاة لتحقيق معايير الاستدامة الاجتماعية وتأثير ذلک علي الترکيب الفراغي للمدينة ,ويقترح البحث مجموعة من المعايير التى تحقق الاستدامة الاجتماعية لمسارات المشاة داخل مرکز المدينة واستعادة الدور الوظيفى والاجتماعى لمسارات المشاة ثم دراسة هذه المعايير المقترحة علي الحالة التطبيقية : شارع الحسيني البحري في محافظة المنيا . تم تقسيم البحث إلى ثلاث محاور، المحور الأول توضيح مفهوم الاستدامة الاجتماعية في البيئة العمرانية. المحور الثاني بناء الإطار العام لمؤشرات وآليات تحقيق الاستدامة الاجتماعيـة لمسارات المشاة ,ولغرض اختبار الفرضية طبقت مؤشرات الإطار النظري على حالة دراسية ( شارع الحسيني البحري في محافظة المنيا )، لکي يخرج البحث بمعاييرحول أليات تحقيق الاستدامة الاجتماعية وتفعيلها لمسارات المشاة ، وذلک ضمن المحور الثالث (الدراسة التطبيقية) وتحليل نتائج التطبيق