The effects of molecular weight on the single lap shear creep and constant strain rate behavior of thermoplastic polyimidesulfone adhesive

The bonded shear creep and constant strain rate behaviors of zero, one, and three percent endcapped thermoplastic polyimidesulfone adhesive were examined at room and elevated temperatures. Endcapping was accomplished by the addition of phthalic anhydrides. The primary objective was to determine the effects of molecular weight on the mechanical properties of the adhesive. Viscoelastic and nonlinear elastic constitutive equations were utilized to model the adhesive. Ludwik's and Crochet's relations were used to describe the experimental failure data. The effects of molecular weight changes on the above mentioned mechanical behavior were assessed. The viscoelastic Chase-Goldsmith and elastic nonlinear relations gave a good fit to the experimental stress strain behavior. Crochet's relations based on Maxwell and Chase-Goldsmith models were fit to delayed failure data. Ludwik's equations revealed negligible rate dependence. Ultimate stress levels and the safe levels for creep stresses were found to decrease as molecular weight was reduced

International Design Engineering Technical Conferences and Computers and Information in Engineering Conference

ABSTRACT We devised a novel technique to fabricate composite cylindrical helical springs using glass, and carbon fibers and in hybrid form, embedded in a matrix of epoxy resin, thus introducing a novel approach to spring making by incorporating the versatility of the filament winder. Our method allows us to vary the dimensions of the spring with considerable ease. This is accomplished in three stages. The first stage involves the proper selection of the resin and hardener. In the next stage, the glass and carbon fibers are completely soaked in a resin bath and encased in PVC tubing of three different inner diameters, which determine the wire diameter of the composite spring. Using a filament winding technique, these fiber filled tubes are wound on PVC mandrels of three different diameters. The natural frequencies of the manufactured composite springs were measured experimentally to study the influence of dimensional parameters, i.e., diameter ratios (D/d) and number of active turns (N = 6 and 7) on the free vibration frequencies. The natural frequencies for glass and carbon fiber and hybrid springs were measured using an MTS fatigue tester, and the resonance of the springs were captured using a digital camera

Temperature-Dependent Phase Behaviors in Cylinder-Forming Block Copolymers

We demonstrate that the temperature-dependent phase behaviors of parallel and perpendicular cylinder-forming block copolymers are governed by domain-domain segregation forces inherently present in block copolymer material itself. With increasing temperature, a parallel cylinder-forming block copolymer experienced a parallel cylinder straightening process before the order-disorder transition (ODT) and did not show long-range composition fluctuations near the ODT temperature due to the weak segregation forces between the block domains. A perpendicular cylinder-forming block copolymer with a strong segregation force between the block domains displayed cylinder orientation transition from perpendicular to parallel below the ODT temperature. On the other hand, a perpendicular cylinder-forming block copolymer material with an exceptionally strong segregation force between the block domains maintained its initial perpendicular cylinder orientation up to near the ODT temperature. In both cases of perpendicular cylinder-forming block copolymers, submicrometer-scale long-range composition fluctuations were observed well above the ODT temperature due to their intrinsically strong segregation forces between the block domains

Complex constitutive adhesive models

A complete approach to modeling adhesives and adhesive joints needs to include considerations for: deformation theories, viscoelasticity, singularity methods, bulk adhesive as composite material, adhesively bonded joint as composite and the concept of the “interphase”, damage models, and the effects of cure and processing conditions on the mechanical behavior. The adherend surfaces have distinct topographies, which result in a collection of miniature joints in micron, and even nano scale when bonded adhesively. The methods of continuum mechanics can be applied to this collection of miniature joints by assuming continuous, or a combination of continuous/discontinuous interphase zones

Classification of Adhesive and Sealant Materials

In this chapter, classification of adhesive and sealant materials is presented. For this purpose, various categories are considered depending on the polymer base (i.e., natural or synthetic), functionality in the polymer “backbone” (i.e., thermoplastic or thermoset), physical forms (i.e., one or multiple components, films), chemical families (i.e., epoxy, silicon), functional types (i.e., structural, hot melt, pressure sensitive, water-base, ultraviolet/electron beam cured, conductive, etc.), and methods of application. The classification covers high-temperature adhesives, sealants, conductive adhesives, nanocomposite adhesives, primers, solvent-activated adhesives, water-activated adhesives, and hybrid adhesives

Recent approaches in constitutive behavior and testing of structural adhesives

Adhesively bonded joints are complex composite structures with at least one of the constituents, namely the adhesive, most often, being a composite material itself due to the presence of secondary phases such as fillers, carriers, etc. The joint structure possesses a complex state of stress with high stress concentrations, and often, singularities due to the terminating adhesive layer where the substrates may possess sharp corners. With these issues in mind, this article discusses the following: Typical joint stress distributions; Stress concentrations and the effect of joint scarf angle on stress concentrations; Singularity methods; Reductions in stress concentrations due to viscoelastic adhesive behavior, as well as increases in joint strength due to rate dependent viscoelastic adhesive behavior; Geometrical methods to reduce stress concentrations; Bulk adhesive as composite material; The concept of the interphase; Damage models; The effects of cure and processing conditions on the mechanical behavior

Geometric effects on multilayer generic circuits fabricated using conductive epoxy/nickel adhesives

Epoxy/nickel adhesives can be used as integrated circuit (IC) packaging materials due to their lower cost than epoxy/silver adhesives with acceptable electrical conductivity. In this work, conductive epoxy/Ni adhesives were prepared by the solution method and filled into holes connecting the multilayers of a novel prototype designed for use in electronic components in circuit boards, in order to study the geometric effects on the prototype\u27s electrical resistance. An empirical equation was obtained for the contact resistance (R c) measured after cure. We also show that Ohm\u27s law adequately describes the effects of the bulk adhesive resistance (R b) on prototype\u27s electrical resistance

Nickel Nanofibers Manufactured via Sol-Gel and Electrospinning Processes for Electrically Conductive Adhesive Applications

The electrospun fibers of poly(vinyl pyrrolidone) (PVP)-nickel acetate (Ni(CH3COO)2·4H2O) composite were successfully prepared by using sol-gel processing and electrospinning technique. Nickel oxide (NiO) nanofibers were obtained afterwards by high temperature calcinations of the precursor fibers, PVP/Ni acetate composite nanofibers, at 700 °C for 10 h. Following with the reduction of NiO nanofibers at 400 °C using hydrogen gas (H2) under inert atmosphere, the metallic nickel (Ni) nanofibers were subsequently produced. In addition, as-prepared Ni nanofibers were chemically coated with silver (Ag) nanoparticles to enhance their electrical property and prevent the surface oxidation. The characteristics of as-prepared fibers, such as surface morphology, fiber diameters, purity, the amount of NiO nanofibers, and metal crystallinity, were determined using a scanning electron microscope (SEM), a Fourier transform infrared spectrometer (FT-IR), a thermogravimetric analyzer (TGA), and a wide-angle x-ray diffractometer (WAXD). The volume resistivity of epoxy nanocomposite filled with Ag-coated short Ni nanofibers was lower than the one containing short Ni nanofibers with no coating due to the synergetic effect of Ag nanoparticles created during the coating process. We also demonstrated that the volume resistivity of epoxy nanocomposite filled with Ni nanofibers could be dramatically decreased by using Ni nanofibers in the non-woven mat form due to their small fiber diameter and high fiber aspect ratio, which yield a high specific surface area, and high interconnecting network