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A common method for understanding the thermal performance of epoxy laminate materials is to analyze the glass transition temperature using instruments such as differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA) and thermomechanical analysis (TMA). In order to characterize the long‐term performance of a finished printed circuit board, more advanced reliable test methods have been developed. This paper will discuss interconnect stress testing (IST), an accelerated fatigue test used for evaluating the failure modes of a printed circuit board (PCB) interconnect. IST utilizes a DC current to heat the PCB to the recommended temperatures within the interconnect. The plated through hole integrity and the post‐interconnect integrity can be monitored simultaneously. The test matrix compares the performance of various AlliedSignal epoxy laminate materials as a function of glass transition temperature (Tg) and board design.

This paper presents a numerical and experimental investigation of ceramic shell cracking during the burnout process in investment casting with internally webbed laser stereolithography patterns. Considered are the cracking temperature of the ceramic shell, the buckling temperature of the web link, and the glass transition temperature of the epoxy resin. Our hypothesis is that shell cracking will occur if the ceramic rupture temperature is lower than the temperature of glass transition and the temperature of web buckling. This hypothesis is validated by a good agreement we obtained between experimental observations and numerical simulations. It is found that the shell cracking and web link buckling are strongly related to the cross‐sectional dimensions and span length of the web structure and the shell thickness, and that shell cracking can be prevented by buckling of the epoxy webbed pattern in early stages of the burnout process.

The build characteristics of two liquid crystal (LC) reactive monomers were studied using a table‐top stereolithography apparatus (TTSLA). LC materials contain stiff, rod‐like mesogenic segments in their molecules, which can be aligned causing an anisotropy in properties. When cured in the aligned state the anisotropic structure is “locked in” resulting in materials with anisotropic physical and mechanical properties. By varying the alignment of layers, properties such as thermal expansion coefficient can be optimized. High heat distortion (or glass transition) temperatures are possible depending on the monomer chemical structure. Working curves for the LC resins were developed under various conditions. A permanent magnet placed outside the TTSLA vat was used to uniformly align the monomer in the nematic state. Photo‐initiator type and content; alignment of the nematic phase; and operating conditions affected the working curve parameters. Glass transition temperatures of post‐cured parts ranged from 75 to 1488C depending on the resin and processing conditions. Mechanical analysis data revealed a factor of two difference between glassy moduli measured in the molecular alignment versus the transverse alignment directions. Based on these initial studies, more advanced resins with higher glass transitions are being developed at the University of Dayton.

Polyurea is an elastomeric two-phase co-polymer consisting of nanometer-sized discrete hard (i.e. high glass transition temperature) domains distributed randomly within a soft (i.e. low glass transition temperature) matrix. A number of experimental investigations reported in the open literature clearly demonstrated that the use of polyurea external coatings and/or internal linings can significantly increase blast survivability and ballistic penetration resistance of target structures, such as vehicles, buildings and field/laboratory test-plates. When designing blast/ballistic-threat survivable polyurea-coated structures, advanced computational methods and tools are being increasingly utilized. A critical aspect of this computational approach is the availability of physically based, high-fidelity polyurea material models. The paper aims to discuss these issues.

In the present work, an attempt is made to develop a material model for polyurea which will include the effects of soft-matrix chain-segment molecular weight and the extent and morphology of hard-domain nano-segregation. Since these aspects of polyurea microstructure can be controlled through the selection of polyurea chemistry and synthesis conditions, and the present material model enables the prediction of polyurea blast-mitigation capacity and ballistic resistance, the model offers the potential for the “material-by-design” approach.

The model is validated by comparing its predictions with the corresponding experimental data.

The work clearly demonstrated that, in order to maximize shock-mitigation effects offered by polyurea, chemistry and processing/synthesis route of this material should be optimized.

The purpose of this paper is to understand the recovery mechanism of poly(trimethylene terephthalate) (PTT) shape memory fabrics.

Tests were designed to study the effects of force, temperature and their combinations on the fabrics' crease recoveries. In the test a cantilever device and an ironing force which simulated people ironing their clothes were used, respectively.

Temperature was found to have little effect on the recovery of both the warp and filling of the fabrics. Crease recoveries did not improve significantly when the temperature was increased to above the polymer's glass transition. However, forces, applied in primarily compressive and tensile modes to simulate ironing and hand stroking actions, were found to be very effective in the fabrics' crease recoveries. Recoveries were 81‐87 per cent even when the applied force was very small, at 5 N/cm². When forces were applied at elevated temperatures, just below and above the polymer's glass transition, there were no significant improvements in crease recoveries. Therefore, force was the main factor in PTT shape memory fabrics' recovery mechanism for the fabrics to return to their initial shapes.

The results suggest that PTT shape memory fabric has excellent shape recoverability and easy care property and it has large application potentiality.

Currently, there is a great demand for those food products that are easy to prepare or ready for direct consumption. Making pear fruit/juice available round the year is desirous owing to pears' high-nutritional value and specific pleasant taste. Pear is, however, a seasonal fruit and under ambient conditions has a limited shelf life rendering it available as fresh fruit for a specific period.

The study aimed to optimize the spray drying process parameters using response surface methodology for the development of pear juice powder. The process variables included the inlet air temperature of 140–210°C, maltodextrin levels of 4–25%, atomization speed of 11,400–28,000 rpm, feed flow rate of 180–630 mL/hr, and feed total soluble solids (TSS) of 13–30°Brix. The dependent responses were powder yield, solubility, antioxidant activity {% 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging capacity}, dispersibility, hygroscopicity and particle density.

Among independent variables, inlet air temperature showed a predominant effect. The optimum processing conditions for the development of pear juice powder with optimum quality were 163.02°C inlet air temperature, 13.50% maltodextrin, 28,000 rpm atomization speed, 390.94 mL/h feed flow rate, and 25.5°Brix feed TSS. Under these optimum conditions, pear powder with desirable properties could be produced. The experimental and predicted values were found to be in agreement, indicating the suitability of the model in predicting optimizing responses of pear powder. Glass transition temperature of pear powder was found to be 36.60 ± 0.40°C, which is much higher than that of ambient temperature, suggesting better shelf stability.

The processing of pear fruit has resulted in the increased demand for pear juice powder in both domestic and international markets as a primer of new food products. The optimum conditions obtained in the current study could provide a new insight to the food industry in developing spray-dried pear powder of optimum quality. This can open up a new horizon in the field of food industry for the common masses of Jammu and Kashmir, India.

The press performance of a range of wool and wool blend fabrics has been investigated with the aid of a temperature adjustable hand steam iron, a domestic ironing board and a thermocouple digital temperature display.It was found that for a press duration of 10 seconds, the fabric crease angle is reduced with the increasing press temperature. The sharpest reduction in crease angle was found in the temperature range of 80°C to 120°C for all fabrics tested.At 100°C iron temperature, the fabric crease angle was reduced with increasing press duration until 20 seconds for wool fabrics and until 30 seconds for wool blend fabrics.The initial regain, or in other words, the relative humidity of the ambient atmosphere used to precondition the samples, has an important influence on the press performance. It was also found that the fabric crease recovery was greater for increasing ambient relative humidity.The fabric regain was greatly reduced during the first 10 seconds pressing time with further very slow reduction in fabric regain until 80 seconds pressing time. The regain in the upper layer of the fabric specimen was always lower than that in the lower layer.

Anisotropic conductive film (ACF) offers miniaturization of package size, reduction in interconnection distance and high performance, cost‐competitive packaging and improved environmental impact. However, a major limitation for ACF is the instability caused by thermal warpage. The purpose of this paper is to study the effects of thermal warpage on contact resistance in real time i.e. make online measurements of contact resistance fluctuations while the assembly undergoes thermal shock.

The ACF assemblies are subjected to thermal cycling with different temperature profiles that have peak temperatures either below or above the glass transition temperature (T_g) of the ACF. The flex substrate used was made of polyimide film, with Au/Ni/Cu electrodes and a daisy‐chained circuit matched to the die bump pattern. The ACF used was based on epoxy resin in which nickel and gold‐coated polymer particles are dispersed. A comparative study was carried out on the results obtained.

The results showed that the glass transition temperature (T_g) of the ACF material plays an important role in the high temperature contact resistance. Above T_g, the ACF matrix becomes less viscous, which reduces its adhesive strength and allows the bumps on the chip to slide away from the pads on the substrate. Even though a flex substrate was used in this study, the sliding effect is severe at the corner bumps of the chip, where cumulative forces are generated due to the thermal expansion mismatch. For every thermal cycling profile, there is an incubation period encountered from this work that would have a significant impact in the application of ACF. After the incubation period the contact resistance increased rapidly and the assemblies were therefore no longer reliable.

The work in this paper focuses on contact resistance changes during thermal shock. The paper discusses the reliability issue of ACF during thermal warpage, which is useful to industries using ACF for flip‐chip assemblies.

The paper aims to investigate the problem of heat distribution in FDM 3D printing. The temperature distribution of the material is important because of the occurrence of shrinkage and crystallization phenomena that affect the dimensional accuracy and strength of the material.

The study uses a thermoplastic material (polylactide) and a test stand equipped with a 3D printer adapted to perform thermographic observations. The main source of heat in the study was a molten laminate material and a hot-end head.

When the material is molten at the temperature of 190°C, the temperature of a previous layer increases above the glass transition point (T_g = 64.8°C) and reaches to about 80°C. In addition, at the boundary of the layers, there occurs a permanent bonding of the consecutive layers because of their partial melting. The paper also reports the results of porosity of PLA samples printed at the temperature ranging between 205 and 255°C. The degree of porosity depends on the temperature of the extruded material.

The results may be helpful for designers of various printed parts and construction engineers of printing heads and 3D printer chambers.

Thermograms of material layers with a height of 0.3 mm are obtained using a thermal imaging camera with a lens for macro magnification (43 pixels/mm).

Recent advancements of 3D printing technology have brought forward the interest for this technique in many engineering fields. This study aims to focus on mechanical properties of the polylactic acid (PLA) feeding material under different thermal conditions for a typical fusion deposition of 3D printer system.

Specimens were tested under static loading within the range 20ºC to 60ºC considering different infill orientations. The combined effect of temperature and filament orientation is investigated in terms of constitutive material parameters and final failure mechanisms. The difference between feeding system before and post-3D printing was also assessed by mechanical test on feeding filament to verify the thermal profile during the deposition phase.

The results in terms of Young’s modulus, ultimate tensile strength (UTS), strain at failure (εf) and stress at failure (σf) are presented and discussed to study the influence of process settings over the final deposited material. Fracture surfaces have been investigated using an optical microscope to link the phenomenological interpretation of the failure with the micro-mechanical behaviour. Experimental results show a strong correlation between stiffness and strength with the infill orientation and the temperature values. Moreover, a relevant effect is related to deformed geometry of the filament approaching glass transition region of the polymer according to the deposition orientation.

The developed method can be applied to optimise the stiffness and strength of any 3D-printed composite according to the infill orientation.

To avoid the failure of specimens outside the gauge length, a previously proposed modification to the geometry was adopted. The geometry has a parabolic profile with a curvature of 1,000 mm tangent to the middle part of the specimen.

Several authors have reported the stiffness and strength of 3D-printed parts under static and ambient temperature for different build parameters. However, there is a lack of literature on the combination of the latter with the temperature effects on the mechanical properties which this paper covers.