Multiple heat isothermal stress rupture correlations for type 316L(N) stainless steel and their use Part 2 – Applications for nuclear grade type 316L(N) stainless steel base metal and its weld metal

Abstract

The 'reference' multiple heat isothermal stress rupture correlations for stainless steel types 316 and 316L(N) base metals derived in Part 1 are used for establishing those for a specific 316L(N) stainless steel base metal and also its weld, both candidates for the forthcoming prototype fast breeder reactor at Kalpakkam. The phases that form in the weld metal during creep are the same as those in the base metal; however, the uniformly distributed δ ferrite ( ~ 7 ferrite number) in vermicular morphology present in the initial microstructure accelerates their formation and increases their quantities, resulting in poorer stress rupture properties. A simple modification allows for correlating and extrapolating the weld data to long rupture lives using the multiple heat isothermal correlations developed for the base metal.     

Interlaminar Stresses at the Delamination Fronts in Tubular Adhesive Joints with Delaminated Composite Adherends

The use of composite materials has been extensively increasing in the recent decades, mainly due to their high strength and stiffness to weight ratios, as well as their non-corrosive attribute. Adhesive joints are used effectively to join composites to composites or to dissimilar materials. Components made of composites may contain some defects in the form of delaminations that may adversely affect their overall behavior and response when subjected to different loading systems. Interlaminar stresses (including out-of-plane stresses) are caused by the mismatch in material properties, especially in Poisson's ratio and the so-called 'coefficient of mutual influence' (between adjacent layers). The goal of this paper is to evaluate the interlaminar stresses that exist at the delamination fronts in a composite pipe, hosting a small delamination, adhesively bonded to an aluminum pipe. The aim is also to study the effect of various parameters (such as delamination length, depth, fiber orientation angles, and stacking sequence) that influence the performance, using the finite element method. The system is subjected to a torsional moment, which can be considered as a critical loading condition in tubular adhesive joints. Results of the study provide valuable information about the behavior of adhesive joints with delaminated composite adherends, and reveal the nature and distribution of interlaminar stresses along various delaminated fronts under torsional moments.     

An energy-based failure criterion for delamination initiation in electronic packaging

The significance of interfacial delamination as a crucial failure mechanism in electronic packaging has been documented in many papers. A number of failure criteria have been used to solve the problems with a pre-crack at the interface. However, in real electronic packages, the size and location of the cracks or/and delamination cannot be predicted. It is not easy to use the traditional fracture criteria to deal with more complicated 3D delamination problems. The epoxy molding compound (EMC)/copper leadframe interface was selected in this study. A series of button shear tests were conducted to evaluate the interfacial adhesion between the EMC and copper. In each test, the failure load acting on the EMC of the button shear sample was measured at different shear angles and a finite element model was used to evaluate the stresses at the EMC/copper interface. In this paper, an energy-based failure criterion is proposed using both the interfacial distortional and hydrostatic strain energy densities as two failure parameters. Stresses were extracted from the numerical simulation in order to calculate the interfacial distortional strain energy density, U _d, and the interfacial hydrostatic strain energy density, U _h, related, respectively, to the shear and tensile modes. U _d and U _h were averaged within a selected region of the finite element model where it exhibits high interfacial strain energy density values.     

Study of adhesion failure due to molding compound additives at chip surface in electronic devices

Today the microelectronics market requires devices with failure levels approaching zero. To attain this goal all production processes must be subjected to extreme quality control. Molding is one of the most critical assembly processes in power plastic packages. This is related to the complexity of phenomena which may occur at the interfaces involved in this process. This paper reports an adhesion study of epoxy-phenolic molding compounds to the most relevant surfaces encountered in power devices assembled in plastic packages such as copper oxide-hydroxide, nickel oxide-hydroxide, aluminium oxide-hydroxide, and silicon 'nitride'. The study was carried out by combining delamination (scanning acoustic microscopy) and pull strength data with the interface chemistry studied using ESCA. Different adhesion failure mechanisms were found to be operative in these systems. These mechanisms are related to either the chemical nature and thickness of the inorganic layer or the segregation of various additives such as wax, polyoxyalkylene ethers, and alkylsiloxanes, contained in the molding compound.     

An experimental investigation of the effect of interface adhesion on the fracture characteristics of a brittle-ductile layered material

The effect of interface adhesion on the failure characteristics of brittle-ductile layered material was experimentally investigated. Single-edge-notched fracture specimens were prepared by bonding two Homalite-100 layers to a thin aluminum layer using three different types of adhesives. The specimens were loaded under three-point bending and photoelasticity was used for full-field observation of the failure process. Fracture tests revealed two competing modes of failure: delamination along the Homalite-aluminum interface, and crack re-initiation in the Homalite layer across the reinforcing aluminum layer. The failure modes were directly influenced by the characteristics of the adhesive bond. Maximum load retention and energy dissipation capability during the fracture process was observed for a urethane based adhesive that formed an interfacial bond that was resistant to delamination, and additionally exhibited low modulus and large strain-to-failure, thereby suppressing crack re-initiation.     

Investigation of Damage Growth in Single Lap Joints of Composite Laminates

In this paper, growths of different types of failures including adhesion, cohesion and delamination for a single lap joint (SLJ) of composite laminates were investigated using three-dimensional geometrically nonlinear finite element analysis and by adopting a suitable modeling technique. A unique damage modeling method called sub-laminate modeling was employed for the modeling of damages of different failure modes so as to avoid the oscillatory stress and displacement fields around the damage front. The strain energy release rate (SERR) parameter was used for studying the damage growth and the individual and total components of the SERR along the various damage fronts are evaluated using the virtual crack closure technique (VCCT) based on the linear elastic fracture mechanics (LEFM) approach. This study reveals: that the opening mode is the dominant mode of the propagation for the adhesion and delamination damages, while the sliding mode is dominant for the cohesion failure; that the cohesion failure grows at a faster rate than the adhesion failure; and that the delamination front entrapped within the overlap region in the top adherend of the SLJ grows faster when the delamination damages are present simultaneously in both the adherends. This is particularly true when the delamination centers are exactly aligned with the overlap ends of the joint.     

Investigation of moisture diffusion in electronic packages by molecular dynamics simulation

Moisture-related failure is one of the main concerns in the integrated circuit (IC) package design. To minimize such failure in multi-layered electronic assemblies and packages, it is important to develop a better understanding of the reliability at a molecular level. In this paper, molecular dynamics (MD) simulations were conducted to investigate the respective moisture diffusion into the epoxy molding compound (EMC) and at the EMC/Cu interface. Moisture diffusion coefficients into the bulk EMC material and at the EMC/Cu interface can be derived from the mean-squared displacements calculated from MD simulations. The MD results showed that the seepage along the EMC/Cu interface is more prevalent when compared to moisture diffusion into the bulk EMC and, thus, rendering it a dominant mechanism causing moisture induced interfacial delamination in plastic packages.     

Wear behaviour of Fe3 Al intermetallic particle reinforced PM based iron metal matrix composites

Abstract

The wear behaviour of unreinforced and reinforced PM based iron metal matrix composite, the latter containing 10 and 20 vol.-% nano sized Fe₃Al intermetallic particles, was studied as a function of sliding distance under two different loads and dry lubricated conditions. The intermetallic Fe₃Al nanoparticles were prepared by mechanical alloying and used as particle reinforcement with 10 and 20 vol.-% in the matrix. The processing of the composites included mixing and cold compaction followed by sintering at 1120°C. The influence of Fe₃Al additions on the dry sliding wear behaviour was studied at loads 20 and 40 N over sliding distances 2160, 3240, 4320 and 6480 m. The study showed that the composite exhibited a lower wear rate than that of the unreinforced matrix and the wear rate was influenced by the volume percentage of Fe₃Al particles. It is understood that iron aluminide reinforcement has a beneficial effect on the wear properties. Delamination and microcutting were the chief mechanisms of wear for the composites.