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Article

Pietro Lanzillotti, Julien Gardan, Ali Makke and Naman Recho

The purpose of this paper is the application and the improvement of a previous method based on an acrylonitrile butadiene styrene thread deposition in fused deposition…

Abstract

Purpose

The purpose of this paper is the application and the improvement of a previous method based on an acrylonitrile butadiene styrene thread deposition in fused deposition modeling. To gain up to 20 per cent of mechanical strength in comparison with a classical deposition, this method suggests a smart threads deposition in the principal stresses direction.

Design/methodology/approach

In this work, the authors use single edge notched bend specimens with mixed mode I+II loading cases to study the influence of the thread deposition on the fracture toughness of the specimens. For this purpose, finite elements simulations have been used to evaluate the fracture toughness of the specimens through the calculation of the J integral. The study presents a method to compare the optimized and classical specimens and also to gather data and suggest a numerical model for this optimized deposition. For this reason, tensile tests are carried out to characterize the mechanical behavior of the printed samples with respect to the raster angle. Extra attention has been paid to 45 per cent samples behavior that shows a pronounced plasticity before the fracture. This interprets partially the improvement in the fracture behavior of the single edge notched bend samples.

Findings

The results show an enhancement through this optimization which leads to an increase of the maximal force in fracture up to 20 per cent and the fracture toughness of the specimens with stress intensity factors KI and KII increases about 30 per cent.

Originality/value

Additive manufacturing is increasingly gaining importance not only in prototyping but also in industrial production. For this reason, the characterization and the optimization of these technologies and their materials are fundamental. An adaptive deposition through a smart material based on specific mechanical behaviors would be an advance.

Details

Rapid Prototyping Journal, vol. 25 no. 4
Type: Research Article
ISSN: 1355-2546

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Article

Kehang Yu, Chen Yang, Jun Wang, Jiabo Yu and Yi Yang

The purpose of this paper is to study the variation of the mechanical strength and failure modes of solder balls with reducing diameters under conditions of multiple reflows.

Abstract

Purpose

The purpose of this paper is to study the variation of the mechanical strength and failure modes of solder balls with reducing diameters under conditions of multiple reflows.

Design/methodology/approach

The solder balls with diameters from 250 to 760 µm were mounted on the copper-clad laminate by 1-5 reflows. The strength of the solder balls was tested by the single ball shear test and pull test, respectively. The failure modes of tested samples were identified by combing morphologies of fracture surfaces and force-displacement curves. The stresses were revealed and the failure explanations were assisted by the finite element analysis for the shear test of single solder ball.

Findings

The average strength of a smaller solder ball (e.g. 250 µm in diameter) is higher than that of a larger one (e.g. 760 µm in diameter). The strength of smaller solder balls is more highly variable with multiple reflows than larger diameters balls, where the strength increased mostly with the number of reflows. According to load-displacement curves or fracture surface morphologies, the failure modes of solder ball in the shear and pull tests can be categorized into three kinds.

Originality/value

The strength of solder balls will not deteriorate when the diameter of solder ball is decreased with a reflow, but a smaller solder ball has a higher failure risk after multiple reflows. The failure modes for shear and pull tests can be identified quickly by the combination of force-displacement curves and the morphologies of fracture surfaces.

Details

Soldering & Surface Mount Technology, vol. 31 no. 4
Type: Research Article
ISSN: 0954-0911

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Article

F.G.A. Silva, M.F.S.F. de Moura, N Dourado , F. A. M. Pereira , J.J.L. Morais , M. I. R. Dias, Paulo J. Lourenço and Fernando M. Judas

Fracture characterization of human cortical bone under pure mode I loading was performed in this work. The purpose of this paper is to validate the proposed test and…

Abstract

Purpose

Fracture characterization of human cortical bone under pure mode I loading was performed in this work. The purpose of this paper is to validate the proposed test and procedure concerning fracture characterization of human cortical bone under pure mode I loading.

Design/methodology/approach

A miniaturized version of the double cantilever beam (DCB) test was used for the experimental tests. A data reduction scheme based on crack equivalent concept and Timoshenko beam theory is proposed to overcome difficulties inherent to crack length monitoring during the test. The application of the method propitiates an easy determination of the Resistance-curves (R-curves) that allow to define the fracture energy under mode I loading from the plateau region. The average value of fracture energy was subsequently used in a numerical analysis with element method involving cohesive zone modelling.

Findings

The excellent agreement obtained reveals that the proposed test and associated methodology is quite effective concerning fracture characterization of human cortical bone under pure mode I loading.

Originality/value

A miniaturized version of traditional DCB test was proposed for cortical human bone fracture characterization under mode I loading owing to size restrictions imposed by human femur. In fact, DCB specimen propitiates a longer length for self-similar crack propagation without undertaking spurious effects. As a consequence, a R-curve was obtained allowing an adequate characterization of cortical bone fracture under mode I loading.

Details

International Journal of Structural Integrity, vol. 6 no. 3
Type: Research Article
ISSN: 1757-9864

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Article

Tao Wang, Zhanli Liu, Yue Gao, Xuan Ye and Zhuo Zhuang

The interaction between hydraulic fracture (HF) and natural fracture (NF) in naturally fractured rocks is critical for hydraulic fracturing. This paper aims to focus on…

Abstract

Purpose

The interaction between hydraulic fracture (HF) and natural fracture (NF) in naturally fractured rocks is critical for hydraulic fracturing. This paper aims to focus on investigating the development of tensile and shear debonding zone on the NF caused by the stresses produced by HF, and the influence of NF’s debonding behavior on the interaction between HF and NF.

Design/methodology/approach

Theoretically, tensile and shear debonding modes of NF are considered, two dimensionless parameters are proposed to characterize the difficulty of tensile and shear failure of NF, respectively. Numerically, a finite element model combining the extended finite element method and cohesive zone method (CZM) is proposed to study NF’s debonding behavior and its influence on the interaction between HF and NF.

Findings

Both theoretical analysis and numerical simulation show the existence of two debonding modes. The numerical results also show that the HF can cross, offset or propagate along the NFs depending on the parameters’ value, resulting in different fracture network and stimulated reservoir volume. When they are large, the NF’s debonding area is small, HF tends to cross the NF and the fracture network is simple; when they are small, the NF’s debonding area is large, HF will propagate along the NF. In addition, HF is easier to propagate along with NF under tensile debonding mode while it is easier to pass through NF under shear debonding mode.

Originality/value

The theoretical and numerical considerations are taken into account in the influence of the debonding of NFs on the interaction between HFs and NFs and the influence on the formation of the fracture network.

Details

Engineering Computations, vol. 36 no. 8
Type: Research Article
ISSN: 0264-4401

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Article

Bin Chen, Song Cen, Andrew R. Barron, D.R.J. Owen and Chenfeng Li

The purpose of this paper is to systematically investigate the fluid lag phenomena and its influence in the hydraulic fracturing process, including all stages of fluid-lag…

Abstract

Purpose

The purpose of this paper is to systematically investigate the fluid lag phenomena and its influence in the hydraulic fracturing process, including all stages of fluid-lag evolution, the transition between different stages and their coupling with dynamic fracture propagation under common conditions.

Design/methodology/approach

A plane 2D model is developed to simulate the complex evolution of fluid lag during the propagation of a hydraulic fracture driven by an impressible Newtonian fluid. Based on the finite element method, a fully implicit solution scheme is proposed to solve the strongly coupled rock deformation, fluid flow and fracture propagation. Using the proposed model, comprehensive parametric studies are performed to examine the evolution of fluid lag in various geological and operational conditions.

Findings

The numerical simulations predict that the lag ratio is around 5% or even lower at the beginning stage of hydraulic fracture under practical geological conditions. With the fracture propagation, the lag ratio keeps decreasing and can be ignored in the late stage of hydraulic fracturing for typical parameter combinations. On the numerical aspect, whether the fluid lag can be ignored depends not only on the lag ratio but also on the minimum mesh size used for fluid flow. In addition, an overall mixed-mode fracture propagation factor is proposed to describe the relationship between diverse parameters and fracture curvature.

Research limitations/implications

In this study, relatively simple physical models such as linear elasticity for solid, Newtonian model for fluid and linear elasticity fracture mechanics for fracture are used. The current model does not account for such effects like leak off, poroelasticity and softening of rock formations, which may also visibly affect the fluid lag depending on specific reservoir conditions.

Originality/value

This study helps to understand the effect of fluid lag during hydraulic fracturing processes and provides numerical experience in dealing with the fluid lag with finite element simulation.

Details

Engineering Computations, vol. 35 no. 5
Type: Research Article
ISSN: 0264-4401

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Article

Zequn Mei and Ali Eslambolchi

Multi‐layer surface finish, from the bottom to top, of electroless Ni, electroless Pd, and immersion Au (Ni/Pd/Au) have been introduced in the printed circuit board (PCB…

Abstract

Multi‐layer surface finish, from the bottom to top, of electroless Ni, electroless Pd, and immersion Au (Ni/Pd/Au) have been introduced in the printed circuit board (PCB) industry recently. This paper reports an evaluation of this surface finish from the perspective of solder joint attachment reliability, especially to see if the Ni/Pd/Au could be immune from the brittle interfacial fracture of PBGA on electroless Ni/immersion Au, recently observed and reported by us. PCBs with Ni/Pd/Au finishes, made from two vendors with varied Pd layer thickness were attached with PBGA packages, and tested in four‐point bending. When joint strength is strong, bending tests resulted in peeling off the PCB pads; otherwise, brittle fractures occurred at the interface between solder balls and PCB pads. After aging, solder joints on all Ni/Pd/Au and reference metal finishes failed by the same brittle fracture at the interface between Ni‐Sn and Au‐Sn intermetallic compounds. It is concluded that the interfacial fracture was controlled by something other than the Pd, and the existence of the Pd did not prevent the interfacial fracture. Also, the presence of Pd could not prevent the Au migration and subsequent fracture.

Details

Circuit World, vol. 25 no. 2
Type: Research Article
ISSN: 0305-6120

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Article

J. Seyyedi, B. Arsenault and J.P. Keller

Quasi shear and tensile mode stress‐rupture and quasi shear mode creep behaviours were investigated for aged production surface mount soldered connections of 127 mm pitch…

Abstract

Quasi shear and tensile mode stress‐rupture and quasi shear mode creep behaviours were investigated for aged production surface mount soldered connections of 127 mm pitch, rigid gullwing and J‐bend configurations at ambient and 60°C (on limited specimens) environments. These joints were manufactured by the vapour phase reflow soldering process using a 63Sn‐37Pb solder composition. Metallographic examinations and fractrographic studies were also performed on appropriate specimens to characterise the metallurgical attributes of the solder and the joint failure. A relatively coarse solder microstructure was observed with both joint configurations. The steady‐state creep data of both soldered joints exhibited two distinct creep regimes. A grain boundary‐controlled regime at low loads with a slope of 042 for gullwing and 0?50 for J‐bend joints was followed by a dislocation climb‐controlled regime at high loads with a slope of 0?13 and 0?24 for gullwing and J‐bend configurations, respectively. The log‐log plot of applied load varied linearly with rupture time for the entire load range for the respective soldered joints for both modes of testing at room temperature. A transgranular fracture morphology was found to predominate for the entire load regime for the quasi shear mode tested gullwing joints. A mixed‐mode fracture morphology with predominantly transgranular features was observed for both low and high loading conditions for quasi shear mode tested J‐bend specimens. The steady‐state creep elongation in shear showed a strong dependence on the applied load for both types of soldered joints. This was primarily attributed to the presence of relatively large creep transients, especially at higher loads.

Details

Soldering & Surface Mount Technology, vol. 3 no. 1
Type: Research Article
ISSN: 0954-0911

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Article

Michał Smolnicki, Mateusz Cieciura, Grzegorz Lesiuk, José Correia and Paweł Stabla

Engineered stone is a material which can be described as an artificial stone. The exemplary application area is sink production. There are very few research projects about…

Abstract

Purpose

Engineered stone is a material which can be described as an artificial stone. The exemplary application area is sink production. There are very few research projects about this type of material. In fact, most of them are research conducted by the manufacturing company, which are limited to the basic properties of the material. However, knowledge about fracture mechanic of this material may be crucial in terms of usage. The paper aims to discuss this issue.

Design/methodology/approach

Analysis of the inside structure was made using an optical microscope as well as SEM. In the paper, methods which can be used to obtain data about fracture behaviour of material are presented. Using eXtended Finite Element Method and experimental data from three-point bending of notched specimens stress intensity factors (SIFs) for I and II load modes were obtained. Finally, a comparison between the fracture initiation angle in the function of the ration of SIFs for I/II load modes and maximum tangential stress hypothesis prediction was presented.

Findings

Analysis of the inside structure proves that this type of material has an uneven distribution of particle size. This can follow to void and micronotches formation and, later, to the failure of the material. A method of obtaining stress intensity factors for the discussed type of material and specimens can be successfully applied to other similar material, as proposed in this work. Standard crack angle propagation criteria are not sufficient for this type of material.

Originality/value

There are very few research papers about this type of material. The subject of fracture mechanic is not properly discovered, despite the fact that IT is important in terms of the application area of these materials.

Details

International Journal of Structural Integrity, vol. 12 no. 1
Type: Research Article
ISSN: 1757-9864

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Article

Luciano Simoni and Stefano Secchi

This paper presents a mathematical model for the analysis of cohesive fracture propagation through a non‐homogeneous porous medium. Governing equations are stated within…

Abstract

This paper presents a mathematical model for the analysis of cohesive fracture propagation through a non‐homogeneous porous medium. Governing equations are stated within the frame of Biot's theory, accounting for the flow through the solid skeleton, along the fracture and across its sides toward the surrounding medium. The numerical solution is obtained in a 2D context, exploiting the capabilities of an efficient mesh generator, and requires continuous updating of the domain as the fractures enucleate and propagate. It results that fracture paths and their velocity of propagation, usually assumed as known, are supplied directly by the model without introducing any simplifying assumption.

Details

Engineering Computations, vol. 20 no. 5/6
Type: Research Article
ISSN: 0264-4401

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Article

K.T. Tsai, F‐L. Liu, E.H. Wong and R. Rajoo

This paper aims to present a new micro‐impact tester developed for characterizing the impact properties of solder joints and micro‐structures at high‐strain rates, for the…

Abstract

Purpose

This paper aims to present a new micro‐impact tester developed for characterizing the impact properties of solder joints and micro‐structures at high‐strain rates, for the microelectronic industry, and the results evaluated for different solder ball materials, pad finishes and thermal histories by using this new tester. Knowledge of impact force is essential for quantifying the strength of the interconnection and allows quantitative design against failure. It also allows one‐to‐one comparison with the failure force measured in a standard quasi‐static shear test.

Design/methodology/approach

An innovative micro‐impact head has been designed to precisely strike the specimen at high speed and the force and displacements are measured simultaneously and accurately during the impact, from which the failure energy may be calculated.

Findings

The paper demonstrates that, peak loads obtained from the impact tests are between 30 and 100 percent higher than those obtained from static shear tests for all combinations of solder alloy and pad finish. The SnPb solder alloy had the maximum energy to failure for all pad finishes. Of all the lead‐free solders, the SnAg solder alloy had the highest energy to failure. Static shearing induces only bulk solder failure for all combinations of solder alloy and pad finish. Impact testing tends to induce bulk solder failure for SnPb solder and a mixture of bulk and intermetallic failure in all the lead‐free solder alloys for all pad finishes. In general, the peak loads obtained for solder mask defined pads are significantly higher than those for non‐SMD (NSMD) pads. The results obtained so far have highlighted the vulnerability of NSMD pads to drop impact.

Practical implications

The work provides a new solution to the microelectronics industry for characterizing the impact properties of materials and micro‐structures and provides an easy‐to‐use tool for research or process quality control.

Originality/value

The new micro‐impact tester developed is able to perform solder ball shear testing at high speeds, of up to 1,000 mm/s, and to obtain fracture characteristics similar to those found in drop impact testing using the JEDEC board level testing method JESD22‐B111 – but without the complexity of preparing specialized boards. This is not achievable using standard low‐speed shear testers.

Details

Soldering & Surface Mount Technology, vol. 18 no. 2
Type: Research Article
ISSN: 0954-0911

Keywords

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