Search results

Understanding the effect of process parameters on interfaces and interfacial bonding between two materials during multi-material additive manufacturing (MMAM) is crucial to the fabrication of high-quality and strong multi-material structures. The purpose of this paper is to conduct an experimental and statistical study to investigate the effect of process parameters of soft and hard materials on the flexural behavior of multi-material structures fabricated via material extrusion-based MMAM.

Sandwich beam samples composed of a soft core and hard shells are fabricated via MMAM under different printing conditions. A design of experiments is conducted to investigate the effect of the print speed and nozzle temperature on the flexural behavior of soft-hard sandwich beams. Analysis of variance and logistic regression analysis are used to analyze the significance of each process parameter. The interfacial morphology of the samples after the flexural tests is characterized. Thermal distributions during the MMAM process are captured to understand the effect of process parameters on the flexural behavior based on inter-bonding formation mechanisms.

Experimental results show that the soft-hard sandwich beams exhibited two different failure modes, including shell failure and interfacial failure. A transition of failure modes from interfacial failure to shell failure is observed as the nozzle temperatures increase. The samples that fail because of interfacial cracking exhibit a pure adhesive failure because of weak interfacial fracture properties. The samples that fail because of shell cracking exhibit a mixed adhesive and cohesive failure. The flexural strength and modulus are affected by the nozzle temperature for the hard material and the print speeds for both hard and soft materials significantly.

This paper first investigates the effect of process parameters for soft and hard materials on the flexural behavior of additively manufactured multi-material structures. Especially, the ranges of the selected process parameters are distinct, and the effect of all possible combinations of the process parameters on the flexural behavior is characterized through a full factorial design of experiments. The experimental results and conclusions of this paper provide guidance for future research on improving the interfacial bonding and understanding the failure mechanism of multi-material structures fabricated by MMAM.

This paper presents an application of the physics‐of‐failure design philosophy to flip‐chip bonds in a microelectronic package. The physics‐of‐failure philosophy utilises knowledge of the life‐cycle load profile, package architecture and material properties to identify potential failure mechanisms and to prevent operational failures through robust design and manufacturing practices. The potential failure mechanisms and failure sites are identified in this paper for flip‐chip bonds, and an approach is presented to prevent the identified potential failure mechanisms by design. Finally, quality conformance issues are discussed to ensure a robust manufacturing process and qualification issues are addressed to evaluate the reliability of the designed flip‐chip bond.

Fibre reinforced polymer composites (FRPs) are finding increasing usage in many industrial sectors. Adhesive bonding is often the most attractive joining technique for these materials in terms of structural efficiency and cost of manufacture. However, concerns regarding the lack of reliable design methods, the long term ageing behaviour and the difficulties in non‐destructive evaluation and repair of bonded joints has led to a reluctance to use adhesives in primary structures. DERA has been involved in the assessment of adhesive bonding for joining FRPs for many years. This paper focuses on investigations at DERA into the effects that environment and fatigue loading have on the performance of bonded composite joints, and briefly reviews current approaches to strength and lifetime prediction. It is seen that adhesively bonded composite joints can be significantly affected by the service environment, however, this is highly dependent on the joint type and materials involved.

Assembling items to achieve bigger parts seems to be the solution to counterbalance the dimension limits of 3D printing. This work aims to propose an approach to achieve optimal assembling.

Acrylonitrile butadiene styrene polymer samples were printed using fused deposition modelling (FDM). These samples were assembled and the precise contribution of interfacial shearing and tension was measured using simple tensile experiments.

The results achieved show the correlation between the printing orientation and the assembling angle. It could be proved that rupture by an interfacial decohesion mechanism of glued parts can be avoided by simple adaptation of the assembling junction.

Design of large parts using FDM is no more a limitation if assembling configurations are adapted based on the knowledge gained about the interfacial phenomena occurring at the junction position.

The unbalanced contribution of shearing and tension at the interface defines new assembling profiles that exclude flat junctions.

Near-surface mounted (NSM) fiber-reinforced polymer (FRP) rod is extensively applied in reinforced concrete (RC) structures. The mechanical performances of NSM FRP-strengthened RC structures depend on the bond behavior between NSM reinforcement and concrete. This behavior is typically studied by performing pull-out tests; however, the failure behavior, which is crucial to the local debonding process, is not yet sufficiently understood.

In this study, a three-dimensional meso-scale finite element method considering the cohesion and adhesion failures is presented to model the debonding failure process in pull-out tests of NSM FRP rod in concrete. The smeared crack model is used to capture the cohesion failures in the adhesive or concrete. The interfacial constitutive model is applied to simulate the adhesion failures on the FRP-adhesive and concrete-adhesive contact interfaces.

The present method is first validated by two simple examples and then applied to a practical NSM FRP system. This work studied in detail the debonding process, the bond failure types, the location of peak bond stress, the transmitting deformation in adhesive and the morphology of contact zone. The developed method provides a practical and convenient tool applicable for further investigations on the debonding mechanism for the NSM FRP rod in concrete.

A three-dimensional meso-scale finite element method considering the cohesion and adhesion failures is presented to model the debonding failure in NSM FRP-strengthened RC structures. The smeared crack model and the interfacial constitutive model are introduced to develop a convenient approach to analyze the failures in adhesive, concrete and related interfaces. The developed numerical method is applicable for studying the debonding process, the bond failure types, the location of peak bond stress, the transmitting deformation in adhesive and the morphology of contact zone in detail.

Due to its inexpensive production costs, low stress concentration and maintenance-friendliness, the adhesive bonded pipe joint is frequently utilized for pipe connection. However, further theoretical analysis is needed to understand the debonding failure mechanism of such bonded pipe joints under axial tension.

In this study, based on the bi-linear cohesive zone model, the integrated closed-form solutions were derived by considering the axial stiffness ratio and failure stage to determine the relative interfacial slip, interfacial shear stress and relationship of tension–displacement in the bonded pipe joint.

Additionally, solutions for the critical bonded length and the ultimate load capacity were put forth. Besides, the numerical study was conducted to verify the theoretical solutions regarding the load–displacement relationship. The interfacial shear stress distribution at different failure stages was presented to understand the interfacial shear stress transmission and debonding process. The effect of bonded length on the ultimate load and ductility of pipe joints was also discussed.

The findings in this study can give a reference for the design of bonded pipe joints in their actual engineering applications.

The purpose of this paper is to present a novel high speed impact testing method for evaluating the effects of low temperatures on eutectic and lead‐free solder joints. Interfacial cracking failure of Sn‐based and Pb‐free solders at subzero temperatures is of significant concern for electronic assemblies that operate in harsh environments.

This paper presents a newly designed low temperature control system coupled with an Instron micro‐impact testing machine, which offers a package level test for solder bumps, and that is used at subzero temperature ranges as low as −40°C. This study examined the failure characteristics of 63Sn‐37Pb (Sn37Pb) and 96.5Sn‐3Ag‐0.5Cu (SAC305) solder joints at temperatures ranging from room temperature (R.T.) to −40°C, and at impact speeds of 1 m/s.

Three types of failure mode were identified: M1 interfacial fracture with no residual solder remaining on the pad (interfacial cracking); M2 interfacial fracture with residual solder persisting on the pad (mixed mode failure); and M3 solder ball fracture (bulk solder cracking). The experimental results indicated that the energy to peak load for both types of solders decreased significantly, by approximately 35 percent to 38 percent when the test temperature was reduced from R.T. to −40°C. In addition, the peak load of the Sn37Pb solder joint increased noticeably with a decreasing test temperature. However, the peak load of the SAC305 specimen remained virtually unchanged with a reduction in the temperature. The Sn37Pb solder joints failed in an M3 failure mode under all the considered testing temperatures. The SAC305 solder joints displayed both M1 and M2 failure modes at R.T.; however, they failed almost exclusively in M1 mode at the lowest test temperature of −40°C.

This paper presents a novel technique for evaluating high‐speed impact strength and energy absorbance of Sn‐based and Pb‐free solders at the chip level within a low temperature control system. To overcome the drawbacks experienced in other studies, this study focused specifically on cryo‐impact testing systems and the performed experimental steps to improve the accuracy of post‐test analysis.

This paper gives a bibliographical review of the finite element methods (FEMs) applied to the analysis of ceramics and glass materials. The bibliography at the end of the paper contains references to papers, conference proceedings and theses/dissertations on the subject that were published between 1977‐1998. The following topics are included: ceramics – material and mechanical properties in general, ceramic coatings and joining problems, ceramic composites, ferrites, piezoceramics, ceramic tools and machining, material processing simulations, fracture mechanics and damage, applications of ceramic/composites in engineering; glass – material and mechanical properties in general, glass fiber composites, material processing simulations, fracture mechanics and damage, and applications of glasses in engineering.

Plastic ball grid array packages were aged for up to 2000 hours. Various solder ball pad metallurgies were studied and solder ball shear tests were conducted at a range of ageing times. The solder ball shear strength was found to decrease after an initial hardening stage. The deterioration of solder ball shear strength was found to be mainly caused by the formation of intermetallic compound layers, together with microstructural coarsening and diffusion related porosity at the interface. For the ball pad metallurgy, two distinct intermetallic compound layer structures were observed to have formed after ageing. Once two continuous intermetallic compound layers formed fracture tended to occur at their interface. For the ball pad metallurgies which do not form two continuous intermetallic compound layers, the shear strength still decreased, due to the coarsening of the microstructure, intermetallic particle formation and diffusion related porosity at the surface of the Ni₃Sn₄.

Glass is a promising interposer substrate for 2.5 D integration; yet detailed analysis of the interfacial reliability of through-glass vias (TGVs) has been lacking. The purpose of this paper is to investigate the design and material factors responsible for the interfacial delamination in TGVs and identify methods to improve reliability.

The interfacial reliability of TGVs is studied both analytically and numerically. An analytical solution is presented to show the dependence of the energy release rate (ERR) for interfacial delamination on the via design and the thermal mismatch strain. Then, finite element analysis (FEA) is used to investigate the influence of detailed design and material factors, including the pitch distance, via aspect ratio, via geometry and the glass and via materials, on the susceptibility to interfacial delamination.

ERR for interfacial delamination is directly proportional to the via diameter and the thermal mismatch strain. Thinner wafers with smaller aspect ratios show larger ERRs. Changing the via geometry from a fully filled via to an annular via leads to lower ERR. FEA results also show that certain material combinations have lower thermal mismatch strains, thus less prone to delamination.

The results and approach presented in this paper can guide the design and development of more reliable 2.5 D glass interposers.

This paper represents the first attempt to comprehensively evaluate the impact of design and material selection on the interfacial reliability of TGVs.