Fatigue Failure Analysis of a Centrifugal Pump Shaft

This chapter deliberates on the systematic processes in failure investigation of engineering components and structures. The procedures are demonstrated in performing failure analysis of a centrifugal pump shaft. The chemical, microstructural, and fractographic analyses provide information on the material science aspects of the failure. The mechanical design analyses establish the cause of failure based on the stress calculations using the strength-of-materials approach. Fatigue analysis using the modified Goodman criterion is employed with consideration of yielding, under the fluctuating load. It is concluded that fatigue crack nucleated in the localized plastic zone at the threaded root region and propagated to cause the premature fatigue failure of the rotor shaft

Vapor pressure development in a FR4-CU composite structure during solder reflow

This article presents a study on the development of vapor pressure a FR4-Cu composite structure when heated to a solder reflow temperature of 215 °C. Abaqus® finite element software was used to develop a representative two-dimensional model of the composite structure and to simulate moisture absorption and desorption processes. Simulation of transient moisture absorption was performed to predict moisture concentration distribution in the structure after being preconditioned in 85°C/85 % RH environment for 15 days. Simulation of transient moisture desorption was carried out at the solder reflow temperature to predict the redistribution of the moisture. Results of the moisture desorption simulation were used to compute magnitude of the vapor pressure in the structure. It was found that the moisture redistributes itself during the solder reflow process. Moisture concentration in the vicinity of the FR4-Cu interface, below the longer copper trace increases during the solder reflow. The vapor pressure in nearly 70 % of the FR4 material and close to the FR4-Cu interface, below the longer copper trace is almost equal to the saturation pressure of vapor at 215 °C. Distribution of the vapor pressure is very similar to the new distribution of moisture concentration resulting from moisture desorption process

Mixed-Mode Delamination Failures of Quasi-Isotropic Quasi- Homogeneous Carbon/Epoxy Laminated Composite

This chapter characterised the delamination behaviour of a quasi-isotropic quasi-homogeneous (QIQH) multidirectional carbon/epoxy-laminated composite. The delaminated surface constituted of 45°//0 layers. Specimens were tested using mode I double cantilever beam (DCB), mode II end-notched flexure (ENF) and mixed-mode I+II mixed-mode flexure (MMF) tests at constant crosshead speed of 1 mm/min. Results showed that the fracture toughness increased with the mode II component. Specifically, the mode I, mode II and mixed-mode I+II fracture toughness were 508.17, 1676.26 and 927.52 N/m, respectively. When the fracture toughness values were fitted using the Benzeggagh-Kenane (BK) criterion, it was found that the best-fit material parameter, η, was attained at 1.21. Furthermore, fibre bridging was observed in DCB specimens, where the steady-state fracture toughness was approximately 80% higher compared to the mode I fracture toughness. Finally, through scanning electron micrographs, it was found that there was resin-rich region at the crack tip of the specimens. In addition, fibre debonding of the 45°layer was found to be dominant in the DCB specimens. Significant shear cusps were noticed in the ENF specimens. As for the MMF specimens, matrix cracking and fibre debonding of the 0°layer were observed to be the major failure mechanisms

Non-Fickian Absorption Characteristics of Adhesive Joints: Capillary Effects and Residual Properties

Mechanical performance of polymer-based adhesive joints is generally susceptible to moisture absorption. This study quantifies the effects of moisture content on the strength, stiffness, and energy properties of adhesive bonded joints. For this purpose, moisture absorption characteristics of structural adhesive joints (Araldite 2015) with different thicknesses (0.5, 1.0, and 1.5 mm) were firstly established under accelerated aging condition (deionized water at 60 oC). A thickness-dependent non-Fickian moisture absorption model was then used to characterize the moisture absorption of the adhesive joints. Results suggested that the moisture absorption of the adhesive joints was governed by the capillary action. Subsequently, adhesive joints with aluminum 6061 adherent and 0.5 mm-thick Araldite 2015 adhesive compound were subjected to dry, 0.1, 0.15, 0.18, and 0.2 pct of moisture content. The specimens were tested in shear and tension loadings at 1 mm/min. The resulting variations in the mechanical properties were fitted using a residual property model. It was noticed that all properties degraded upon moisture attack. For strength and energy properties, the degradation was more severe in tension. As for the stiffness, the decrease in the property was similar in both tensile and shear. The results from this study showed that moisture attack is an important aspect to be considered when designing for the service lifetime of adhesive bonded structures

Effect of fiber misalignment on tensile response of unidirectional cfrp composite lamina

Mechanical responses and failure of fiber-reinforced polymer (FRP) composite laminates could be predicted using the validated finite element (FE) simulation. The material constitutive and damage models employed in the simulation are developed based on the properties of the unidirectional lamina, including those obtained through tension tests. Such computational model assumes perfectly aligned fibers in the lamina. In this respect, this paper examined the effect of fabrication-inherited fiber misalignment on the tensile response of the unidirectional lamina. For this purpose, a series of tension tests are performed on unidirectional carbon fiber-reinforced polymer (CFRP) composite lamina specimens with different gage lengths ranging from 50 to 150 mm. Fiber misalignment is quantified to be 7o and represents the nominal deviation of the fibers from the reference longitudinal axis direction. Load-displacement responses of the specimens are compared. Results show that the nominal tensile strength of the lamina is 1089±33 MPa. The elastic modulus, however, increases from 36.96 to 55.93 GPa as the gage lengths vary from 50 to 150 mm, respectively. This is due to the induced bending effects on the reinforcing fibers that is greater for longer gage lengths. Multiple fiber fracture events, each is depicted in a noticeable load drop, are recorded throughout the tensile loading of long lamina specimens. Although the load at fracture is accurately reproduced by the FE simulation using the damage-based mesoscale model, the effect of fiber misalignment could not be captured

Effects of welding on the microstructural properties of AISI 43 ferritic stainless steel

Ferritic stainless steel (FSS) are engineering alloys with high strength, improved ductility and better corrosion resistance in environments containing various compounds of chloride, normally experienced in petrochemical and nuclear power industries. However ferritic stainless steel suffer some weldability issues like grain growth at heat effected zone (HAZ), martensite and carbide formation at grain boundaries, sensitization and intergranular stress corrosion cracking. In this study AISI 430 butt TIG welding is investigated for these issues. The investigations reveal the presence of martensites and carbides in the grain boundaries along with coarse grain structure in HAZ and FZ. The increased hardness and strength at weld zone causes FSS to have low ductility and prone to cracking in stress environment

Design And Development Of Auto-Steel Draw Forming Test Device

This work is concerned with the design and development of draw forming test device with double action draw forming mechanism.This device is designed to operate on universal testing machine (UTM).The dual phase auto-steel about 1.2 mm thick is used as deformable blank.The double action mechanism is generated by an external hydraulic system to equally apply the blank holder force (BHF).Hence,the punch force is driven by UTM’s hydraulic system.The design load and die displacement is initially predicted by FE simulation at maximum load of 123kN and 14 mm displacement respectively.Draw forming result shows the fracture is recorded at 108 kN of punch force and 9.5 mm of displacement depth

Effects of cell aspect ratio and relative density on deformation response and failure of honeycomb core structure

The extensive applications of honeycomb (HC) core in sandwich structures necessitates the influence of the cellular geometry and cell wall base material on the mechanical response to be quantified. In this respect, this paper establishes the mechanics of the deformation and the failure processes of the HC core under the out-of-plane compressive, tensile, and shear loading. The corresponding mechanical properties are determined and the mechanisms of failure of the HC core structure are identified. The influence of the relative density (ρ∗/ρ s) and the cell aspect ratio (H/c) of the hexagonal HC core on the compressive deformation response, the out-of-plane properties and the characteristic dissipation energy density (DED) of the structure is established. Results show that the compressive strength increases exponentially from 1.5 to 10.6 MPa over the relative density range of 0.028 ≤ (ρ∗/ρ s) ≤ 0.125. The out-of-plane shear modulus, G 13 and G 23 are 33.9 and 58.2 MPa, while the shear strength, τ 13 and τ 23 are 1.07 and 2.03 MPa, respectively. The HC core with a low aspect ratio (H/c < 2.64) failed due to the early debonding of the double-wall hexagonal cells, while at H/c ≥ 2.64, by elastic buckling of the cells. A phenomenological model is formulated to highlight the combined effects of both parameters on the compressive strength (σ c) of the HC cores, covering the range of 0.028 ≤ (ρ∗/ρ s) ≤ 0.056 and 2.5 ≤ (H/c) ≤ 5.62. Furthermore, the characteristic dissipation energy density (DED) under the out-of-plane compression varies linearly within the range of 2.5 < (H/c) < 5.62 for the HC core with ρ∗/ρ s = 0.056. The HC core with H/c = 3.96, but with twice higher ρ∗/ρ s exhibits about twice larger DED. These resulting properties and failure mechanisms of the anisotropic paper-based HC core are useful for the validation of the predictive computational models

Moisture absorption effects on mode II delamination of carbon/epoxy composites

It is necessary to consider the influence of moisture damage on the interlaminar fracture toughness for composite structures that are used for outdoor applications. However, the studies on the progressive variation of the fracture toughness as a function of moisture content M (%) is rather limited. In this regard, this study focuses on the characterization of mode II delamination of carbon/epoxy composites conditioned at 70 °C/85% relative humidity (RH). End-notched flexure test is conducted for specimens aged at various moisture absorption levels. Experimental results reveal that mode II fracture toughness degrades with the moisture content, with a maximum of 23% decrement. A residual property model is used to predict the variation of the fracture toughness with the moisture content. Through numerical simulations, it is found that the approaches used to estimate the lamina and cohesive properties are suitable to obtain reliable simulation results. In addition, the damage initiation is noticed during the early loading stage; however, the complete damage is only observed when the numerical peak load is achieved. Results from the present research could serve as guidelines to predict the residual properties and simulate the mode II delamination behavior under moisture attack

Effects of water-cement ratio and notches to the flexural strength of concrete

It is often assumed that flexural strength of concrete has less significance impact on overall concrete strength. However, from fracture mechanics point-of-view tensile is an element the mechanics always look into due to cracking does associate with tension. In the research, fracture is translated into physical laboratory experiment by introducing notches. Physical laboratory works on concrete beams with three-point bend test configuration under static load and calculating outputs from laboratory with numerical equations. Three-point bend test method is conducted because from the testing, tensile strength or also recognised as flexural strength of concrete for each water-cement ratio could be attain. Thus, the aim of this article is to reveal and discuss the pattern of flexural strength of concrete on different water-cement ratio. The testing follows conventional fracture three-point bend test on concrete but with revised version by testing notched concrete beams. Normal three-point bend tests were run on concrete beams with different notch sizes; 30 mm, 15mm, and 5 mm respectively. There were three water-cement ratio decided in concrete mix; 0.3, 0.4, and 0.5. Thus, the trend of flexural strength of concrete follows the trend of water-cement ratio. Flexural strength increases when water-cement ratio increases up to water-cement ratio 0.5