Micro-mechanics Research on Tensile Mechanical Behavior of UHPC Specimen

Effect of artificial aging on the mechanical performance of (Al-Cu) 2024 and (Al-Cu-Li) 2198 aluminum alloys

This paper presents a numerical and experimental study on woven fabric reinforced composites containing co-cured plies joints in order to analyze the effect of butt joints staggered with different distances on the tensile mechanical behavior. Numerical simulations based on finite element method were performed to obtain the stress response of the specimens with embedded butt joints under tensile loads and the regions where the failures occurred for each staggered distance studied in accordance with Puck failure criterion. Tensile tests were executed on specimens whose staggered distances varied in 25, 15, 10, and 5 mm and the results of each family of laminates were compared with a baseline laminate (continuous fibers). The experimental results showed a reduction on the tensile failure load up to 26% compared to the reference laminate. Statistical analyses showed that the staggered distances of 15 mm presented better mechanical performance. SEM analyses revealed similar fractographic aspects on the fracture surface of the specimen with different staggered distances, characterized by a cohesive failure of the matrix originated by the butt joints, with a presence of a strong interfacial adhesion with the weft fibers and interfacial sliding with the warp fibers. The numerical simulation results presented a good agreement with the experimental ones.

This paper presents the results of a numerical simulation of the ultimate flax fibre ( Linum usitatissimum) tensile mechanical behaviour using finite element analysis. Experimental data were used to develop a numerical multilayer model of the flax fibre. Thus, the influence of some parameters, such as cell wall thicknesses, microfibrils angles (MFAs), biochemical composition and mechanical properties of the biochemical components, on the flax fibre tensile mechanical behaviour has been investigated. Results show that the typical stress–strain curve profile of the flax fibre could be due to the mechanical properties of hydrophilic components (hemicelluloses) and thus to the environmental conditions. A parameter sensitivity study reveals that ultrastructural parameters (hemicelluloses and cellulose Young’s modulus) strongly influence the flax fibre mechanical behaviour and structural parameters (S2 cell wall layer MFA and thickness) significantly influence the fibre longitudinal Young’s modulus. Thus, the knowledge of the fibre ultrastructure seems to be the key of the understanding of the flax fibre mechanical behaviour.

Relationship between the structure of injection-molded isotactic polypropylene and its tensile mechanical properties, necking and fracture behaviors in particular, was investigated in terms of micrometer-scale structural inhomogeneity of nanometer- and subnanometer-scale structures. To clarify the micrometer-scale inhomogeneity, we employed scanning microbeam wide-angle X-ray diffraction and small-angle X-ray scattering technique. Four isotactic polypropylene samples were studied, produced using different injection-condition and thermal treatments. The results of scanning microbeam X-ray scattering measurements showed the presence of two types of micrometer-scale structural inhomogeneity in addition to the orientation of molecules: the distribution of polymorphs and of crystalline ordering. The results of scanning microbeam X-ray scattering of deformed sample showed the disappearance of the β-form isotactic polypropylene crystals at the outer regions accompanied by the plastic deformation. It is indicated that the inhomogeneous distribution of crystalline ordering and the existence of different polymorphs are highly related to the tensile mechanical behavior.

The reactive compatibilization of polypropylene/polyethylene terephthalate (PP/PET) blends by addition of glycidyl methacrylate grafted PP (PP‐g‐GMA) was studied. Two PP‐g‐GMA copolymers, containing either 0.2 or 1.2 wt% of GMA, were used as interface modifiers. These were incorporated into PP blends (with either 70 or 90 wt% PET), replacing 1/5 of PP in the system. The use of these modifiers changed the blends' tensile mechanical behavior from fragile to ductile. Blend tensile strength was improved by 10% and elongation at break showed 10 to 20‐fold increases while stiffness remained constant. Scanning electron micrographs showed the PP average domain size in injection molded specimens to decrease to the micron/sub‐micron size upon addition of the GMA modified resins, while the unmodified blends exhibited heterogeneous morphology comprising large lamellae 10–20 μm wide. The low‐GMA graft content PP seemed slightly more efficient than the high GMA content PP in emulsifiying PP/PET blends. The GMA grafting level on PP had very limited effects on the blends' mechanical behavior in the range of GMA graft density provided by the two modified resins investigated.

In this study, we have thoroughly investigated the tensile mechanical behavior of monolayer XN (X = Ga, In) using molecular dynamics simulations. The effects of temperature (100 to 800 K) and point vacancies (PVs, 0.1 to 1%) on fracture stress, strain, and elastic modulus of GaN and InN are studied. The effects of edge chiralities on the tensile mechanical behavior of monolayer XN are also explored. We find that the elastic modulus, tensile strength, and fracture strain reduce with increasing temperature. The point defects cause the stress to be condensed in the vicinity of the vacancies, resulting in straightforward damage. On the other hand, all the mechanical behaviors such as fracture stress, elastic modulus, and fracture strain show substantial anisotropic nature in these materials. To explain the influence of temperature and PVs, the radial distribution function (RDF) at diverse temperatures and potential energy/atom at different vacancy concentrations are calculated. The intensity of the RDF peaks decreases with increasing temperature, and the presence of PVs leads to an increase in potential energy/atom. The current work provides an insight into adjusting the tensile mechanical behaviors by making vacancy defects in XN (X = Ga, In) and provides a guideline for the applications of XN (X = Ga, In) in flexible nanoelectronic and nanoelectromechanical devices.

Tensile mechanical properties and fracture behavior of monolayer InSe under axial tension

Nanostructures with high surface area to volume ratio, such as oxidized and coated Cu nanowires (NWs), exhibit unique mechanical properties due to their size and surface effects. Understanding the complex oxidation process of Cu NWs at nanoscale and quantifying its resulting effects on mechanical behavior and properties are significantly essential for effective usage of Cu NW devices in a wide range of applications in nanoelectronics. Here, we perform molecular dynamics simulations using ReaxFF (reactive force field) to investigate the oxidation process and mechanisms of [001]-oriented cylindrical Cu NWs and its contribution on the mechanical deformation behavior and material properties as a function of NW sizes. The relatively thin oxide CuxOy layer is formed on the surface of Cu NWs in an O2 environment, creating a core/shell (Cu/CuxOy) NW structure that played a key role in governing the overall tensile mechanical deformation behavior and properties of Cu NW. The formation of oxide layer effects, including the resulting interface and defects, leads to a reduction in the initial dislocation nucleation barrier, which facilitates the onset of plasticity and stress relaxation, ultimately resulting in a negative impact on the tensile strength, Young's modulus, yield stress and strain, and flow stress when compared to pristine counterparts. It is worth noting that the tensile mechanical response and properties of the Cu NWs are highly dependent on the pre-existing oxide shell layer associated with the size of NW, determining the overall mechanical performance and properties of Cu NWs.

The tensile mechanical behavior and spall response of a selective laser melted (SLM) 17-4 precipitation-hardening (PH) stainless steel were studied comprehensively through tensile test, plate impact experiment and microstructure characterization in the present study. The results reveal a steel with significant strain rate dependence on the tensile mechanical behavior and spall response. As the strain rate increases, the tensile yield stress increases, but there is no monotonic variation trend for the peak stress; grain structure remains unchanged first and then becomes fine; high-angle grain boundaries (HAGBs) increase; the martensite phase decreases at first and then increases. There is a close correlation among impact velocity, strain rate, peak stress, Hugoniot elastic limit (HEL) and spall strength. Strain rate, peak stress and HEL increase, while spall strength remains almost constant with the increase of impact velocity. As impact velocity increases, grain structure becomes fine, HAGBs increase and the martensite phase increases. The significant phase transformation is responsible for the tensile mechanical behavior and spall response, and the temperature rise was calculated to analyze its effect on phase transformation. Whether the preferred orientations are along the building direction or tensile direction is dependent on strain rate. Tensile and spallation specimens exhibit the ductile fracture mode and the damage originates from voids. It is interesting that the voids always tend to nucleate at melt pool boundaries. A spall damage evolution model is illustrated to describe the damage process.

Description of nonlinear viscoelastic behavior and creep-rupture time of anisotropic conductive film

Chirality, temperature, and vacancy effects on mechanical behavior of monolayer zinc-sulfide

The rate responses of unidirectional fiber composites at low strain rate level (range from 2E-5 to 2E-2 s-1), including tensile mechanical and stress relaxation behaviors, were investigated in this article. The results obtained showed that the ultimate tensile stress increases as strain rate increases, and the stress relaxation time decreases as pre-tensile strain rate increases. And besides, the macro-failure modes of fiber composites changed from ductile fracture feature to brittle fracture feature as strain rate increasing. Furthermore, the micro-failure modes of multi-fiber composite were investigated originally, with the results indicating that fiber-fiber interactions decreased while increasing tensile strain rate.

Tensile mechanical properties and fracture behavior of tungsten heavy alloys at 25–1100 °C

The effects of 30 years of storage on the mechanical behavior and hierarchical structure of isotactic polypropylene were characterized. In addition, the structure and properties of the aged samples exposed to subsequent annealing were assessed. The long-term storage caused a dramatic loss of ductility, as manifested by the strain-at-break and impact strength data. The embrittlement was accompanied by a distinct increase in the crystallinity of both the alpha and beta phases, as revealed by X-ray diffraction. The dynamic mechanical behavior was influenced, but insignificantly. A comparison of static and dynamic mechanical data suggests the development of structural heterogeneities in the amorphous phase of the semicrystalline material upon aging. Under mechanical stress, these heterogeneities serve as fracture loci. Subsequent annealing of the aged samples partly reversed the loss of ductility. This indicates healing of the hypothetical irregularities by the thermal treatment. In addition, annealing caused complete transformation of the beta crystallites into the alpha phase. Long-term storage of isotactic polypropylene caused a dramatic loss of ductility, as manifested by the mechanical tensile and impact behavior. The embrittlement was accompanied by an increase in the crystallinity. A comparison of static and dynamic mechanical data suggests the development of structural heterogeneities upon aging that serve as fracture loci under mechanical stress. Subsequent annealing of the aged samples reversed the loss of ductility. This indicates healing of the hypothetical irregularities by the thermal treatment.

The mechanical tensile fracture behavior was examined for solid-state-annealed eutectic SnPb and lead-free solder flip chip bumps. Annealing temperatures were in the range of 125 to 170°C for 500 hrs. Prior to the solid state annealing, the eutectic Sn-37Pb (SnPh) and Sn-0.7Cu (SnCu) solders showed fracture through the bulk solder. The brittle interfacial fracture occurred in 'Sn-3.5Ag (SnAg) solder. After solid state annealing, the fracture behavior changed dramatically. For eutectic SnPb solder, the fracture modes gradually changed from cohesive solder failure to interfacial fracture with increasing annealing temperature. The fracture mode of SnAg solder showed greater change. At 125°C SnAg had a ductile taffy pull fracture, hut an increase in temperature resulted in brittle interfacial fracture again. SnCu solder maintained the same ductile taffy pull mode up to 170°C annealing, independent of UBM type. Microstructure analysis showed that the interfacial fracture of SnPb and SnAg solder bumps was ascribed to Pb-rich layer formation and Ag emhrittlement at the interface, respectively. The hulk solder fracture of SnAg annealed at 125'C appeared to be a transient phenomenon due to the abrupt breakdown of hard lamella structure. Eutectic SnCu solder bumps had no significant change in the interfacial structure, except for interfacial intermetallic growth. I. Introduction The integrity of solder interconnection is a challenging issue in the packaging of VLSI devices due to the critical need for a large number of the InpuUOutput (VO) connections.[l,2] To achieve the challenging VO needs, flip chip technology is believed to be the key solution. Sn-Pb alloy has been the most widely used solder alloy for interconnects because of excellent soldering properties over a wide range of composition. However, the toxicity of Ph has driven many countries to legislate a ban of Pb-containing solders in electronic devices.[3] A significant numbers of studies on lead-free solders have been performed to remove the Pb from the solder.[4,5] These works have shown that the high content of Sn with several percents of alloying elements would he the good candidates. Even small alloying elements greatly modify the microstructure and mechanical properties of the solder alloys. Typical examples are eutectic Sn-3.5Ag (SnAg) and Sn-0.7Cu (SnCu) solders, discussed in depth elsewhere.[6,7] The bulk properties of various lead-free solders have been studied extensively[8,9] whereas the interfacial mechanical properties at solder joint (between LIEM and solder) with a variety of lead-free solders have not been thoroughly studied. In particular, solder joint properties after solid state aging requires additional study because the device operation temperature is high and increasing over time. In the present study, the mechanical tensile fracture behavior of the flip chip bumps (eutectic SnPb, SnAg, and SnCu) was analyzed for various annealing temperatures. The evolution of solder microstructure and solder joint morphology was investigated to analyze the different fracture modes. The effect of microstructure and interfacial properties on the tensile fracture mode for each solder alloy is presented. II. Experimental Procedure The samples analyzed in this study were prepared by a flip chip bumping process. The passivation (via) opening was 90 pm and the diameter of solder ball was around 150 pm after reflow. For tensile testing, two Si dice (one with solder humps and the other without solder humps) were placed against each other and reflowed to form the solder joint. After die-to-die assembly, the samples were solid-state-annealed for 500 hrs at 125, 150, and 17OoC, respectively. The annealed samples were tested in tension using a screw drive leadframe (Instron machine) at a strain rate of 0.1 /min. The tested samples were characterized by SEM to determine the failure modes. For the analysis of microstructural evolution and interfacial morphology, the samples were cross-sectioned and polished down to a 0.05 pm finish. The polished samples were inspected by both SEM and optical microscope. EDX was used to perform chemical analysis.