Measurement of Bulk Mechanical Properties and Modeling the Load-Response of Rootzone Sands. Part 1: Round and Angular Monosize and Binary Mixtures

The bulk mechanical properties of two different types of rootzone sands (round and angular) were measured using a cubical triaxial tester. Two monosize sands (d 50 = 0.375 mm and 0.675 mm) and their 50:50 binary mixtures (d 50 = 0.500 mm) were studied. The compression, shear, and failure responses of the above-mentioned six compositions were analyzed, compared, and modeled. Two elastic parameters (bulk and shear moduli) and two elastoplastic parameters (swelling and consolidation indices) of the six sand compositions were also calculated and compared. The angular sand was more compressible than round sand during isotropic compression. In addition, the angular sands tended to have lower initial bulk density and high porosity values. Among the three different size fractions, the 0.375 mm mixture was least compressible for both sand shapes. The failure strength and shear modulus of the angular sand were higher than the round sands. In addition, due to their simplicity, phenomenological models were developed to predict the compression and shear behavior of the sands. The prediction models were validated using subangular and subround sands. Average relative difference values were calculated to determine the effectiveness of the prediction models. The mean average relative difference values for compression profiles, i.e., volumetric stress vs. volumetric strain, were from 16 % to 39 %, except for the initial load-response portion (< 1 % volumetric strain). The predictive models were effective in reproducing the failure responses: at 17.2 kPa confining pressure, the mean of average relative difference was 23 %; at 34.5 kPa , the mean difference was 24 %.     

Thermal and hygroscopic reliability of flip-chip packages with an anisotropic conductive film

Thermal and hygroscopic reliability of anisotropic conductive film (ACF) joints in relation to flip-chip bonding force was evaluated by thermal shock and constant temperature/humidity testing. The failure mode by thermal shock testing varied with increasing bonding force, i.e., (1) formation of a conduction gap between conductive particles and Au bump or Ni/Au plated Cu pad at low bonding force and (2) delamination of adhesive matrix from the plated Cu pad on the flexible substrate at high bonding force. The delamination initiated as a crack under a conductive particle and propagated sideward resulting in a complete delamination of the ACF from the Cu pad. However, delamination was observed between the ACF and Au bump on the chip side after the constant temperature/humidity testing for 500 h. A theoretical calculation was also conducted to predict the connection resistance of the ACF joint before and after reliability tests. The calculation showed the importance of the bonding gap between the electrodes.     

Theoretical and experimental studies for the failure criterion of adhesively bonded joints

The objective of this work was to develop a criterion for predicting the failure strength of joints bonded by ductile adhesives. To obtain the criterion, first, fracture tests were carried out on T-peel joints and single-lap joints with various joint geometries, adhesives, and adherend materials. Then using the fracture loads obtained in the tests, a finite element analysis was performed by which the stresses in the adhesive joints were calculated. It is concluded that the failure of an adhesively bonded joint occurs when the maximum of the ratio of the mean to effective stresses exceeds a certain value, which can be considered a new material constant of a ductile adhesive.     

A failure criterion for debonding between encapsulants and leadframes in plastic IC packages

A failure criterion for debonding initiation between molding compounds and copper leadframes in plastic encapsulated integrated circuit (IC) packages is proposed. The leadframe pull-out test is used to evaluate the bond strengths between molding compounds and leadframes in plastic encapsulated IC packages. The normal and shear stress fields along the interface are analyzed using the finite element method. An average stress approach is employed for the interface failure criterion and the tensile and shear interface bond strengths are obtained from the experimental failure loads. In a parametric study, the effects of specimen loading geometry, moisture, and surface contamination of copper leadframes on the interfacial bond strengths are specifically analyzed. The results show that the interface bond strengths determined for the two specimen geometries are consistent.     

Strength and failure of bulky adhesive joints with adhesively-bonded columns

Strength and failure properties of bulky (i.e. with thick substrate) adhesive joints with adhesively-bonded columns (ABCs) subjected to external loads were investigated experimentally and analytically. From the experimental results, it was found that the strengths of the bulky adhesive joints with ABCs increased considerably when they were subjected to external tensile loads or lateral bending loads. And the joint strengths increased with increasing depths of the blind holes. The failure process of the joints with ABCs was simulated by the technique of element birth and death developed in the finite element method (FEM). The conclusions obtained from FEM coincide with those obtained from the experiments.     

Failure analysis of some petrochemical plant components

Abstract

Failure analysis of five sections of plant (the cooling elbow of a chlorination reactor, electrolyte feed pipelines, tubes from an ethylene cracking furnace, the upper pressure cover of the chlorination reactor and heat exchanger tubing) in a petrochemical factory were investigated. Their microstructures were observed using optical and scanning electronic microscopy with compositional analysis measured using energy dispersive X-ray analysis. Mass loss experiments in the laboratory using selected materials and the working environment were also conducted. The main causes of the corrosion of the parts are discussed. Based on the results of the failure analysis, methods to improve the life of the parts are suggested. For example, by selection of suitable substitute alloys the working life of the parts may be increased.     

Finite Element Based Design and Adhesion Failure Analysis of Bonded Tubular Socket Joints Made with Laminated FRP Composites

This paper deals with Finite Element Analysis of bonded Tubular Socket Joints (TSJs) made with laminated Fibre Reinforced Plastic (FRP) composite structures. The effective coupling length for suitable performance of the joint is determined based on the Tsai–Wu failure criterion. The analysis revealed the three-dimensional nature of the stresses and are found to be concentrated in the close vicinity of the free edges and junction of the adherends in the coupling region of the bonded TSJ. Shear stress ( τ_r ), though comparatively small in magnitude, is found to be extremely sensitive to three-dimensional effects as compared to stresses τ_zr and σ_r . Failure indices at different critical interfaces are determined using Quadratic Failure Criterion (QFC) within the adhesive and Tsai–Wu coupled stress criterion for the adherend–adhesive and socket–adhesive interfaces. Based on the latter criterion, locations prone to adhesion failure initiation are identified to be existing near the free edges of the adherend–adhesive interfaces in the coupling region of the bonded TSJ. Strain Energy Release Rate (SERR) calculated using Modified Crack Closure Integral (MCCI) vis-à-vis Virtual Crack Closure Technique (VCCT) has been used as the characterizing parameter for assessing the growth of adhesion failures. The adhesion failure damages have been observed to propagate at the same rate in a self-similar manner mainly in the in-plane shearing mode. Quasi-isotropic and angle-ply orientations of the FRP composite laminates are more resistant to opening mode growth of failure, whereas cross-ply and unidirectional oriented socket/adherends offer better resistance to in-plane shearing mode of adhesion failure damage growth. Plies oriented in the direction of the applied load, especially Graphite/Epoxy (Gr/E) [90]₁₆, are found to offer the best resistance to all types of adhesion failure growth modes and hence are the most preferred fibre orientations for the bonded TSJ under tension. Increasing the degree of anisotropy of the composite socket/adherends improves the adhesion failure damage growth resistance of the bonded TSJ. Boron/Epoxy (B/E) FRP composites are found to be the best in slowing down the growth rate of the adhesion failures among the various FRP composite socket/adherends considered in the present study.     

Risk assessment in pressure equipment inspection: review of recent applications in Jiangsu

Abstract

The application of risk based inspection (RBI) technology in five typical cases in Jiangsu Province, China was summarised and reviewed. Based on 10 year experiences of risk assessment, some key problems, which require special attention in the process of publicising and applying RBI technology in China, were put forward, and the integrity management of pressurised equipment and the qualification requirement for organisation undertaking the RBI projects were emphasised as well. Responses to RBI demands from Chinese petrochemical enterprises were analysed and recommended to be categorised into three groups. To conduct RBI successfully in China, the importance of combining a first rank RBI software and a well organised RBI team is proposed. A sinicised database of materials and chemicals owing to Chinese intellectual property is suggested to be built gradually as well.     

Mechanical and fatigue behaviour of laser and resistance spot welds in advanced high strength steels

Abstract

A study was carried out on laser and resistance spot welds in overlapped sheets of dual phase advanced high strength steel (DP780) and deep drawing steel (DC04) of 2˙0 mm in thickness. The aim of the study was to investigate the fatigue performance of these joints under tensile shear loading as well as the monotonic performance for applications in the automotive industry. The mechanical properties, failure behaviour and fatigue life analyses of spot welds in similar and dissimilar joints were investigated by experimental and numerical methods. The structural stress concept was used to describe the fatigue lives of spot welded specimens. The results revealed different failure types with different fatigue behaviours for laser and resistance spot welds under the application of cyclic loads at 'high load' and 'low load' levels.