Mechanical Characterization of Assemblies Bonded With Pressure-Sensitive Adhesives (PSAs)

2015 ◽  
Author(s):  
Hao Huang ◽  
Abhijit Dasgupta ◽  
Ehsan Mirbagheri ◽  
Srini Boddapati
Keyword(s):  
Mechanical Behavior ◽  
Failure Modes ◽  
Mechanical Characterization ◽  
Bonding Temperature ◽  
Process Conditions ◽  
Second Phase ◽  
Loading Conditions ◽  
Stress Strain ◽  
Strain Behavior ◽  
Pressure Sensitive

The focus of this paper is on the stress-strain behavior and creep response of a pressure-sensitive adhesive (PSA) with and without carrier layers. This study consists of two phases. The first phase focuses on understanding of the effects of fabrication profiles, including bonding pressure, bonding temperature, bonding time, and aging time, on the PSA joint strength. This part of the study is used to identify an acceptable bonding and aging conditions for manufacturing a robust PSA bonded assembly. Specimens fabricated with this selected set of bonding process conditions are then used for mechanical characterization. The second phase focuses on the assembly’s mechanical behavior (stress-strain behavior and the creep curves) under different loading conditions, including loading stress, loading rate, and loading temperature. The mechanical behavior of PSA bonded assemblies is affected not only by the loading conditions, but also by the assembly architecture. The mechanical behaviors and failure modes of PSAs with and without carrier layers are compared. The reasons for these differences are also discussed.

Creep Response of Assemblies Bonded With Pressure Sensitive Adhesive (PSA)

2018 ◽  
Author(s):  
Hao Huang ◽  
Qian Jiang ◽  
Abhijit Dasgupta ◽  
Ehsan Mirbagheri ◽  
Krishna Darbha
Keyword(s):  
Hydrostatic Stress ◽  
Experimental Results ◽  
Double Layers ◽  
Material System ◽  
Secondary Creep ◽  
Loading Conditions ◽  
Stress Strain ◽  
Creep Response ◽  
Strain Behavior ◽  
Pressure Sensitive

Creep response of joints bonded with single-layered pressure sensitive adhesives (PSAs) was investigated in this study. PSAs are becoming more and more popular in the electronic industry as bonding media because of their ease of design, fast accurate bonding, environmentally-friendly bonding and ease of reworking. Such adhesive bonds are expected to experience complex, sustained loading conditions in service; e.g. loading due to large mass components, shock, temperature, or alignment mismatch of substrates. Stress-strain behavior of PSA bonding assembly has been extensively studied through experiments and simulations, including the effects of loading conditions (loading rate and temperature), PSA configurations (thickness of adhesive and single/double-layered PSAs), and bonding substrate surface properties (substrate material and surface roughness). However, the literature regarding the creep response of PSA-bonded assemblies is lacking and there is no literature on modeling methodologies for the creep response of such bonding systems. Similar to the stress-strain behavior of PSA-bonded assemblies, the creep response includes transitions between multiple hardening and softening phases. Experimental results indicate that the secondary creep rate can change by up to two orders of magnitude after each transition, which is too significant to ignore when estimating the creep deformation of joints bonded with this material system. The number of transitions is related to the configuration of the PSA system, i.e. the single-layered PSA has one transition while double-layers PSAs may have multiple transitions due to the additional interface(s) introduced by the carrier layer. This unique secondary creep behavior comes from the competition between hydrostatic stress relaxation and strain hardening, caused by cavitation and fibrillation processes, respectively. The total stress applied on the joint is equal to the summation of deviatoric stress and hydrostatic stress. An advanced model based on the stress-strain ‘block’ model [5–7] is developed for evaluating the creep response. This model has the capability to control the initiation and growth of cavities in the bulk of the PSA and at the interface between PSA and substrate. This model is able to capture the nonlinear visco-plastic behavior of the PSA fibrils and estimate the effects of flexible carrier layer on the transitions in creep curves. The model prediction shows reasonable agreement with experimental results in terms of the characteristic features in creep strain histories.

Studies on the Stress-Strain Relationship Bovine Cortical Bone Based on Ramberg–Osgood Equation

2019 ◽  
Vol 141 (4) ◽  
Author(s):  
N. K. Sharma ◽  
M. D. Sarker ◽  
Saman Naghieh ◽  
Daniel X. B. Chen
Keyword(s):  
Cortical Bone ◽  
Linear Regression Analysis ◽  
Tensile Tests ◽  
Uniaxial Tensile ◽  
Loading Conditions ◽  
Stress Strain ◽  
Strain Behavior ◽  
Nonlinear Stress ◽  
Strain Relationship ◽  
Relationship Of

Bone is a complex material that exhibits an amount of plasticity before bone fracture takes place, where the nonlinear relationship between stress and strain is of importance to understand the mechanism behind the fracture. This brief presents our study on the examination of the stress–strain relationship of bovine femoral cortical bone and the relationship representation by employing the Ramberg–Osgood (R–O) equation. Samples were taken and prepared from different locations (upper, middle, and lower) of bone diaphysis and were then subjected to the uniaxial tensile tests under longitudinal and transverse loading conditions, respectively. The stress–strain curves obtained from tests were analyzed via linear regression analysis based on the R–O equation. Our results illustrated that the R–O equation is appropriate to describe the nonlinear stress–strain behavior of cortical bone, while the values of equation parameters vary with the sample locations (upper, middle, and lower) and loading conditions (longitudinal and transverse).

Effects of Moisture Exposure on the Mechanical Behavior of Polymer Encapsulants in Microelectronic Packaging

2013 ◽  
Author(s):  
Nusrat J. Chhanda ◽  
Jeffrey C. Suhling ◽  
Pradeep Lall
Keyword(s):  
Mechanical Properties ◽  
Mechanical Behavior ◽  
Testing Machine ◽  
Adsorbed Water ◽  
Ultimate Tensile Stress ◽  
Stress Strain ◽  
Uniaxial Test ◽  
Organic Structure ◽  
Strain Behavior ◽  
Humidity Chamber

Polymer encapsulants exhibit evolving properties that change significantly with environmental exposures such as moisture uptake, isothermal aging and thermal cycling. In this study, the effects of moisture adsorption on the stress-strain behavior of a polymer encapsulant were evaluated experimentally. The uniaxial test specimens were exposed in an adjustable thermal and humidity chamber to combined hygrothermal exposures at 85 °C/85% RH for various durations. After moisture preconditioning, a microscale tension-torsion testing machine was used to evaluate the complete stress-strain behavior of the material at several temperatures. It was found that moisture exposure caused plasticization and strongly reduced the mechanical properties of the encapsulant including the initial elastic modulus and ultimate tensile stress. Reversibility tests were also conducted to evaluate whether the degradations in the mechanical properties were recoverable. Upon fully redrying, the polymer was found to recover most but not all of its original mechanical properties. As revealed by FTIR, some of the adsorbed water had been hydrolyzed in the organic structure of the epoxy-based adhesive, causing permanent changes to the mechanical behavior.

Mechanics of Wavy Network With Diamond-Shaped Inclusions

2017 ◽  
Author(s):  
Mona Monsef Khoshhesab ◽  
Yaning Li
Keyword(s):  
Mechanical Properties ◽  
Finite Element ◽  
Mechanical Behavior ◽  
Geometric Constraints ◽  
Cellular Solids ◽  
Biomedical Devices ◽  
Stress Strain ◽  
Engineering Applications ◽  
Smart Composites ◽  
Strain Behavior

In this investigation, mechanical behavior of periodic cellular solids with diamond-shaped inclusions connected via wavy network were explored. Two families of cellular solids within this category were designed based on two different geometric constraints. Auxetic effects and snap-through instability were observed for each family, respectively. The mechanical properties, including the stress-strain behavior, stiffness and Poisson’s ratio, were systematically quantified via finite element (FE) simulations. The parametric space for auxetic effects and snap-through instability was numerically identified. This study demonstrates the connection and transition between mechanical auxeticity and snap-through instability. The materials designed have potential engineering applications, such as lightweight supporting and protective foams, biomedical devices, smart composites or fabrics with switchable properties responsive to external environments.

A laboratory study of normally consolidated kaolin clay

2005 ◽  
Vol 42 (1) ◽  
pp. 27-37 ◽  
Author(s):  
Amit Prashant ◽  
Dayakar Penumadu
Keyword(s):  
Mechanical Behavior ◽  
Pore Pressure ◽  
Principal Stress ◽  
Failure Criteria ◽  
Kaolin Clay ◽  
Specimen Preparation ◽  
Testing Methods ◽  
Stress Strain ◽  
True Triaxial ◽  
Strain Behavior

In recent years many researchers have attempted to address the need for a comprehensive understanding of the three-dimensional mechanical behavior of frictional materials. Advances in testing methods have added the capability of studying various aspects of generalized stress–strain behavior in a controlled environment. Strain-controlled true triaxial undrained tests on normally consolidated kaolin clay are performed in this study using a fully automated flexible boundary experimental setup with a real-time feedback control system. The influence of the intermediate principal stress and principal stress rotation on the stress–strain–strength and pore pressure behavior is investigated considering the occurrence of strain localization within the specimen. The strength behavior observed in this study of kaolin clay is used to evaluate existing failure criteria for cohesive soil. Comparative laboratory tests, such as the lubricated end triaxial test on a solid cylindrical kaolin specimen and combined axial–torsional tests on a hollow cylindrical kaolin specimen, were also performed to evaluate the corresponding mechanical behavior in different loading systems. Despite using identical techniques for specimen preparation and a similar consolidation stress state, the soil behavior obtained from the three types of tests showed observable variations, demonstrating the importance of specimen shape and loading–boundary conditions.Key words: normally consolidated clay, stress-strain behavior, pore pressure, anisotropy, testing methods.

A continuum constitutive model for mechanical behavior of 5052 resin epoxy containing various percentages of MWCNTs

2016 ◽  
Vol 51 (17) ◽  
pp. 2423-2434 ◽  
Author(s):  
SA Hosseini Kordkheili ◽  
H Toozandehjani ◽  
H Ashouri Choshali ◽  
S Boroumand Azad
Keyword(s):  
Constitutive Model ◽  
Mechanical Behavior ◽  
Stress Strain ◽  
Multiwalled Carbon ◽  
Strain Behavior ◽  
Finite Element Software ◽  
Tension Tests ◽  
User Material Subroutine ◽  
Particular Solution ◽  
Acceptable Agreement

In this article, a continuum-based constitutive model is developed to predict the mechanical behavior of 5052 resin epoxy reinforced by multiwalled carbon nanotubes (MWCNTs) based on experimentally generated data. For this purpose, MWCNTs/epoxy specimens with various percentages of functionalized and nonfunctionalized MWCNTs are prepared. The SEM graphs indicate that functionalization leads to a better bound between epoxy and MWCNTs and a higher level of dispersion. The specimens are then tested under standard ASTM D638-02 a procedure and their true plastic stress–strain curves are extracted. Investigations on experimentally generated data reveal that a wt% dependent equation which is obtained using any two series of these data can be successfully implemented for others. The equation is then implemented into a finite element software using a developed user material subroutine in which is utilized based on a particular solution algorithm. In order to verify the accuracy of the model some tensile as well as load-unload-reload tension tests are performed according to standard conditions and acceptable agreement between the numerical and experimental results are observed. Results also indicate that the proposed empirical model can precisely predict the stress–strain behavior of 5052 resin epoxy containing arbitrary wt% of MWCNTs in the range 0–1 wt%.

Effect of Hydrolysis on Mechanical Behavior of Bioabsorbable Composites

2014 ◽  
Vol 783-786 ◽  
pp. 1274-1279 ◽  
Author(s):  
Satoshi Kobayashi ◽  
Shusaku Yamaji
Keyword(s):  
Mechanical Behavior ◽  
Interfacial Strength ◽  
Nonlinear Behavior ◽  
Critical Energy ◽  
Stress Strain ◽  
Critical Energy Release Rate ◽  
Strain Behavior ◽  
Strain Relationship ◽  
Theoretical Results ◽  
Good Agreement

In this study, effect of hydrolysis in simulated body environment on mechanical behavior oftricalcium phosphate (TCP)/Poly(L-lactic acid) (PLLA) composites were analytically characterized.In order to predict stress-strain behavior after hydrolysis, damage micromechanical analysis proposedby the authors were utilized. In this model, nonlinear behavior in stress strain relationship weresimulated considering interfacial debonding between TCP particle and PLLA matrix. For the purposeof deciding the interfacial strength, such as critical energy release rate, curve fitting was conducted onthe result of the composites with 15wt% TCP content. Theoretical results on 5wt% and 10wt%composites using the interfacial strength obtained were in good agreement with experimental results.This result indicated that interfacial strength was independent from TCP fraction.

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