Defect-free Samples Research Articles

Evaluating of bonding strength of pine, oak and nyatoh wood species related to their surface roughness

The objective of this study was to evaluate bonding strength of samples from three wood species, namely pine (Pinus strobus), white oak (Quercus alba) and nyatoh (Palaquium balance). Defect free samples were sanded with 80-, 100- and 240-grit sandpaper before their surface roughness was quantified employing a stylus type profilometer. Samples were bonded in the form of pairs to each other using polyvinyl acetate (PVAc) at a spread rate of 0.15g/cm2 by compressing for 24h. The specimens of nyatoh sanded with 80-grit sand paper resulted in the highest average roughness value of 14.75μm. The same samples also showed the highest bonding strength of 527.35N among the others. It appears that stylus type equipment can be used to evaluate and differentiate roughness of such species due to grit size of sandpaper. Having rougher surfaces of the samples revealed that their higher bonding strength values can be achieved.

Electromigration in Sintered Nanoscale Silver Films at Elevated Temperature

Sintered nanoscale silver is a promising interconnection material for semiconductor devices because it provides improved joint properties compared with solder and wire bonds. It has higher electrical and thermal conductivity and is capable of higher operating temperature. Joints with die shear strength above 20 MPa can be formed at around 250°C even without applied pressure. Sintered silver joints were also found to be an order of magnitude more reliable than solder joints and wire bonds. In this work, the electromigration behavior of sintered nanosilver material under conditions of high applied current density and elevated temperature was investigated. Thin strips of sintered nanosilver formed on ceramic substrates were tested under current densities exceeding 150 kA/cm2 at temperatures of 150°C and above. Results based on the percentage change in sample resistance showed that the sintered silver lasted at least ten times longer than aluminum wire bonds. Examination of failed strips revealed that hairline cracks formed during sintering were the main cause of failure. Otherwise, defect-free samples exhibited a 10-fold increase in lifetime over wire bonds under similar conditions.

Effect of post-weld heat treatment and electrolytic plasma processing on tungsten inert gas welded AISI 4140 alloy steel

Post-weld heat treatment (PWHT) is commonly adopted on welded joints and structures to relieve post-weld residual stresses; and restore the mechanical properties and structural integrity. An electrolytic plasma process (EPP) has been developed to improve corrosion behavior and wear resistance of structural materials; and can be employed in other applications and surface modifications aspects. In this study the effects of PWHT and EPP on the residual stresses, micro-hardness, microstructures, and uniaxial tensile properties are explored on tungsten inert gas (TIG) welded AISI-4140 alloys steel with SAE-4130 chromium–molybdenum alloy welding filler rod. For rational comparison all of the welded samples are checked with nondestructive Phased Array Ultrasonic Testing (PAUT) and to ensure defect-free samples before testing. Residual stresses are assessed with ultrasonic testing at different distances from weld center line. PWHT resulted in relief of tensile residual stress due to grain refinement. As a consequence higher ductility but lower strength existed in PWHT samples. In comparison, EPP-treated samples revealed lower residual stresses, but no significant variation on the grain refinement. Consequently, EPP-treated specimens exhibited higher tensile strength but lower ductility and toughness for the martensitic formation due to the rapid heating and quenching effects. EPP was also applied on PWHT samples, but which did not reveal any substantial effect on the tensile properties after PWHT at 650°C. Finally the microstructures and fracture morphology are analyzed using scanning electron microscopy (SEM) and optical microscope to study the evolution of microstructures.

Nondestructive Evaluation of Poor-Wetted Lead-Free Solder Bumps in Ball Grid Array Packages Using Laser Ultrasound and Interferometric Technique

A laser ultrasound and interferometer inspection system has been successfully applied to detect solder bump defects, including missing, misaligned, open, and cracked solder bumps in flip chips, land grid array packages and chip capacitors. This system uses a pulsed Nd:YAG laser to induce ultrasound in the chip packages in the thermoelastic regime; it then measures the transient out-of-plane displacement response on the package surface using a laser interferometer. The amplitudes of the out-of-plane displacement responses are usually in the order of nanometer. The quality of solder bumps is evaluated by analyzing the transient responses. In this paper, this system is used to evaluate the quality of lead-free solder bumps in ball grid array (BGA) packages; specifically, BGA packages with poor wetted solder bumps are used as test vehicles. Poor wetting not only decreases the mechanical strength of interconnection at the interface between the solder bumps and substrate, but also deteriorates electrical and thermal performance because of the unreliable connections between the package and the printed circuit board (PCB). Causes of poor wetting vary from the solder materials themselves to the manufacturing process. Here, poor wetting of solder bumps were intentionally created by using an improper reflow profile. The transient out-of-plane displacement signal responses from these packages are compared to a hybrid reference signal generated by signal responses from defect-free samples. Packages with poor wetted solder bumps are distinguished from the normal packages by using the correlation coefficient signal analysis method. Then, laser ultrasound inspection results are also compared with results from continuity test, X-ray inspection and scanning acoustic microscope (SAM). Finally, the cross-section images are further used to confirm the existence of the poor wetting in samples with unusual correlation coefficient. It can be concluded that this laser-ultrasound system is capable of identifying the presence of poor wetting in BGA packages.

Deformation and heat treatment of NiAl-Y2O3-based powder alloys: I. Deformation and production of various pressed sections

The effect of a hot extrusion regime for workpieces produced by calcium hydride reduction (CHR) of mechanically activated powders of an NiAl intermetallic alloy and an NiAl-Y2O3 alloy composite on their deformability is studied to form various (round, flat, lens-shaped) sections. The extrusion regimes that make it possible to produce defect-free samples of the NiAl-Y2O3 alloy composite with a metal-deformed structure without traces of dynamic recrystallization are developed. Deformed semifinished samples are formed.

Quantifying the influence of live crown ratio on the mechanical properties of clear wood

Conceptual models of wood formation suggest that trees with large crowns produce wood with reduced mechanical properties due to enhanced auxin production, but few studies have explicitly examined the relationship between crown dimensions and wood properties. Using white spruce (Picea glauca (Moench) Voss) trees harvested from spacing and thinning trials in central Ontario, Canada, this study examines how live crown ratio influences the strength and stiffness of wood. Modulus of rupture (MOR) and modulus of elasticity (MOE) were measured by conducting three-point bending tests on small (150 ×10×10 mm) defect-free samples selected from different radial positions at three heights within the stems. MOR and MOE were strongly and positively related to cambial age, and also increased slightly with sampling height. In addition, MOR showed a significant decrease with increasing live crown ratio ‐ calculated as the ratio of crown length to tree height ‐ in both the spacing and the thinning trials. However, MOE decreased significantly with live crown ratio only in the spacing trial, where the younger trees had a larger range of crown ratios. These results provide tentative support for models of wood formation that link wood quality with crown development, suggesting that crown metrics could be used to predict wood properties before harvest, but doing so may be problematic in mature stands that exhibit less variability in crown dimensions.

AFM investigation of the mechanism for microwave effect on ferroelectric triglycine sulfate

Relation between the microwave effect on ferroelectric triglycine sulfate and the crystal structure dynamics is studied within the concept of ferroactive medium evolution. It is shown that the effect is most distinct in defect-free samples and correlates with the domain structure dynamics. Domain walls are considered to be responsible for structure-sensitive characteristics of triglycine sulfate.

Microstructure and Properties of Selective Laser Melted High Hardness Tool Steel

Abstract A secondary hardening tool steel material X110CrMoVAl 8-2 was successfully processed by selective laser melting (SLM), producing defect free samples of high density. The microstructure appeared irregular after SLM, which was attributed to locally different temper states in consequence of the SLM process pattern. By a subsequent heat treatment, a homogeneous microstructure with ultrafine carbide precipitations and a very high resulting hardness of 765 HV were achieved. The hardness came very close to that of the same material processed by spray forming and forging, whilst the SLM microstructure was significantly finer. Therefore this tool steel material was considered as highly promising for SLM manufacturing of tools, e.g. for micro tooling applications.

Microstructural characterization and formation of α′ martensite phase in Ti–6Al–4V alloy butt joints produced by friction stir and gas tungsten arc welding processes

The obtained microstructures of a Ti–6Al–4V alloy welded by Gas Tungsten Arc Welding (GTAW) and Friction Stir Welding (FSW) were investigated and evaluated quantitatively. In the GTAW method, the effect of current was examined so that the samples were subjected to various currents between 90 and 120A. In the FSW process, samples were welded by different rotational speeds (450–850rpm). Non-destructive tests including Visual and Radiography Tests (VT and RT) were used to identify defect-free samples. The microstructural studies by electron microscopes revealed formation of different phases in the weld area of the samples welded via mentioned methods. The recorded peak temperatures in the weld regions compared favorably with the expectations about the evolved microstructures. A bi-modal microstructure was just obtained in the FSWed sample with a peak temperature below β transus temperature (T<995°C). α′ martensite phase, which is an acicular and strengthening phase in this alloy, was only observed in FSWed specimens.

A fast regularity measure for surface defect detection

In this paper, we propose a fast regularity measure for defect detection in non-textured and homogeneously textured surfaces, with specific emphasis on ill-defined subtle defects. A small neighborhood window of proper size is first chosen and they slide over the entire inspection image in a pixel-by-pixel basis. The regularity measure for each image patch enclosed in the window is then derived from the eigenvalues of the covariance matrix formed by the variance–covariance of the x- and y-coordinates with the pixel gray levels as the weights for all pixel points in the window. The two eigenvalues of the weighted covariance matrix will be approximately the same when the image patch contains only a homogeneous region, whereas the two eigenvalues will be relatively different if the image patch in the window contains a defect. The smaller eigenvalue of the covariance matrix is then used as the regularity measure. The integral image technique is introduced to the computation of the regularity measure so that it is invariant to the neighborhood window size. The proposed method uses only one single discrimination feature for defect detection. It avoids the use of complicated classifiers in a high-dimensional feature space, and requires no learning process from a set of defective and defect-free training samples. Experimental results on a variety of material surfaces found in industry, including textured images of plastic surfaces and leather and non-textured images of backside solar wafers and LCD backlight panels, have shown the effectiveness of the proposed regularity measure for surface defect detection. It is computationally very fast, and takes only 0.032 s for a 400 × 400 image on a Pentium 3.00 GHz personal computer. In a test set of 73 backside solar wafer images involving 53 defect-free and 20 defective samples, the proposed regularity measure can correctly identify all the test images.

Crack Detection in Full Size Cz-Silicon Wafers Using Lamb Wave Air Coupled Ultrasonic Testing (LAC-UT)

With increasing demand for solar energy, the need for reliable inspection systems has increased tremendously. In this paper, a combination of air coupled ultrasonics and Lamb waves have been utilized to frame a crack detection system. Monocrystalline and polycrystalline silicon wafers of 200 μm thickness were used for experimentation and theoretical Lamb mode dispersion curves were plotted for Lamb wave generation in these wafers. A set of defect-free and cracked samples were scanned and the results are presented in this paper. A complete laboratory based cracked detection system was developed and the demonstrated to detect cracks in silicon wafers.

Compositional Dependence of the Compressive Yield Strength of Fe-Nb(-Al) and Co-Nb Laves Phases

ABSTRACTLarge, defect-free single-phase samples of the hexagonal C14 NbFe2 and Nb(Fe,Al)2, and the cubic C15 NbCo2 Laves phases have been produced by a modified levitation melting technique. The compressive strength of NbFe2 and NbCo2 has been determined in dependence on the Nb content, that of Nb(Fe,Al)2 in dependence on the Al content. The binary phases did not show either a maximum (defect softening) or minimum (defect hardening) in strength when the Nb content was varied. Instead, for both phases an increase of the compressive strength with increasing Nb content is observed.

Synthesis of defect-free single-phase bars of high-melting Laves phases through modified cold crucible levitation melting

Laves phases are the most abundant intermetallic phases. However, their mechanical properties are only poorly understood due to difficulties in producing defect-free samples which are large enough for mechanical testing. By using a modified cold crucible levitation melting technique with in situ heat treatment and subsequent defined cooling, massive and large bars of several hundreds of grams of brittle and high-melting Laves phases were produced. Metallographic investigation revealed single- or near single-phase microstructures and a homogeneous chemical composition within the cast ingots with a diameter of 15 mm and of more than 100 mm length. With these high-quality bars it is now possible to prepare large samples that can be used for obtaining mechanical data of these phases.

Relating mechanical strength at the stem level to values obtained from defect-free wood samples

Stem or branch failure is a recurrent problem in silviculture and arboriculture. The risk of rupture varies with species in relation to the inherent mechanical properties of the species and the presence of defects. In general, calculations of critical loads for breakage are based on mechanical properties determined from defect-free samples and adjustment factors that try to scale up to full trees that include defects. This study aims at developing an objective method to scale up mechanical resistance to breakage from defect-free samples to full trees, including different types of defects. It combines two approaches. In the first one, a correction factor is determined from a meta-analysis of various tree-pulling studies involving balsam fir [Abies balsamea (L.) Mill.], white spruce [Picea glauca (Moench) Voss], jack pine [Pinus banksiana Lamb.], and black spruce [Picea mariana (Mill.) B.S.P.]. The second approach consists in obtaining empirical data from three-point bending tests using 8-foot (2.44 m) logs with various amounts of decay. Results show that the correction required varies according to the species and the presence of some defects. For balsam fir, which was the species showing the most important difference between whole log and small sample values, differences in correction factors were found between tree-pulling tests and three-point bending tests. Data from winching tests tend to underestimate the stem’s resistance to breakage since they likely represent the weakest trees among those tested. No relationship was found between the adjustment factors and different indices used in arboriculture to account for decay, showing the complexity of mechanical resistance at the stem level.

Ultraviolet-to-visible image conversion microscopy using photoluminescence from self-assembled CdSe/ZnCdMgSe quantum dots and quantum wells

A high-resolution ultraviolet (UV)-to-visible image conversion microscope using photoluminescence emitted from self-assembled CdSe/ZnCdMgSe quantum dots (QDs) and quantum wells has been developed. This novel microscope exhibits a 1 microm lateral resolution with possible estimated lateral resolution of 200 nm using defect-free QD samples and UV micro-objective with higher numerical aperture and field of view.

Amorphous Semiconductors Studied by First-principles Simulations: Structure and Electronic Properties

AbstractAtomistic models of amorphous solids enable us to study properties that are difficult to address with experimental methods. We present a study of two amorphous semiconductors with a great technological importance, namely a- Si:H and a-SiN:H. We use first-principles density functional theory (DFT), i.e. the interatomic forces are derived from basic quantum mechanics, as only that provides accurate interactions between the atoms for a wide range of chemical environments (e.g. brought about by composition changes). This type of precision is necessary for obtaining the correct short range order. Our amorphous samples are prepared by a cooling from liquid approach. As DFT calculations are very demanding, typically only short simulations can be carried out. Therefore most studies suffer from a substantial amount of defects, making them less useful for modeling purposes. We varied the cooling rate during the thermalization process and found it has a considerable impact on the quality of the resulting structure. A rate of 0.02 K/fs proves to be sufficient to prepare realistic samples with low defect concentrations. To our knowledge these are the first calculations that are entirely based on first-principles and at the same time are able to produce defect-free samples. Because of the high computational load also the size of the systems has to remain modest. The samples of a-Si:H and a-SiN:H contain 72 and 110 atoms, respectively. To examine the convergence with cells size, we utilize a large cell of a-Si:H with a total of 243 atoms. As we obtain essentially the same structure as with the smaller sample, we conclude that the use of smaller cells is justified. Although creating structures without any defects is important, on the other hand a small number of defects can give valuable information about the structure and electronic properties of defects in a-Si:H and a-SiN:H. In our samples we observe the presence of both the dangling bond (undercoordinated atom) and the floating bond (over-coordinated atom). We relate structural defects to electronic defect states within the band gap. In a-SiN:H the silicon-silicon bonds induce states at the valence and conduction band edges, thus decreasing the band gap energy. This finding is in agreement with measurements of the optical band gap, where increasing the nitrogen content increases the band gap.

Thermal stability studies of CVD-grown graphene nanoribbons: Defect annealing and loop formation

We present a high temperature heat treatment study of CVD-grown graphene nanoribbons annealed up to 2800°C, demonstrating a progressive annihilation of lattice defects as the heat treatment temperature is raised. Starting at 1500°C, single and multiple loop formation were observed on the ribbons edges as the temperature was increased. The structural changes of the samples are documented by X-ray diffraction, Raman spectroscopy, TGA, SEM, and HRTEM. This work indicates that nanoribbon annealing eventually leads to defect-free samples, through graphitization and edge loop formation. The annealed material exhibits structural differences that could be tailored for a variety of specific applications.

A Review of Recent Advances in Surface Defect Detection using Texture analysis Techniques

In this paper, we systematically review recent advances in surface inspection using computer vision andimage processing techniques, particularly those based on texture analysis methods. The aim is to reviewthe state-of-the-art techniques for the purposes of visual inspection and decision making schemes that areable to discriminate the features extracted from normal and defective regions. This field is so vast that itis impossible to cover all the aspects of visual inspection. This paper focuses on a particular but importantsubset which generally treats visual surface inspection as texture analysis problems. Other topics related tovisual inspection such as imaging system and data acquisition are out of the scope of this survey.The surface defects are loosely separated into two types. One is local textural irregularities which is themain concern for most visual surface inspection applications. The other is global deviation of colour and/ortexture, where local pattern or texture does not exhibit abnormalities. We refer this type of defects as shadeor tonality problem. The second type of defects have been largely neglected until recently, particularly whencolour imaging system has been widely used in visual inspection and where chromatic consistency plays animportant role in quality control. The emphasis of this survey though is still on detecting local abnormalities,given the fact that majority of the reported works are dealing with the first type of defects.The techniques used to inspect textural abnormalities are discussed in four categories, statistical approaches,structural approaches, filter based methods, and model based approaches, with a comprehensivelist of references to some recent works. Due to rising demand and practice of colour texture analysis inapplication to visual inspection, those works that are dealing with colour texture analysis are discussedseparately. It is also worth noting that processing vector-valued data has its unique challenges, which conventionalsurface inspection methods have often ignored or do not encounter.We also compare classification approaches with novelty detection approaches at the decision makingstage. Classification approaches often require supervised training and usually provide better performancethan novelty detection based approaches where training is only carried out on defect-free samples. However,novelty detection is relatively easier to adapt and is particularly desirable when training samples areincomplete

Motif-based defect detection for patterned fabric

This paper proposes a generalized motif-based method for detecting defects in 16 out of 17 wallpaper groups in 2D patterned texture. It assumes that most patterned texture can be decomposed into lattices and their constituents—motifs. It then utilizes the symmetry property of motifs to calculate the energy of moving subtraction and its variance among different motifs. By learning the distribution of these values over a number of defect-free patterns, boundary conditions for discerning defective and defect-free patterns can be determined. This paper presents the theoretical foundation of the method, and defines the relations between motifs and lattice, from which a new concept called energy of moving subtraction is derived using norm metric measurement between a collection of circular shift matrices of motif and itself. It has been shown in this paper that the energy of moving subtraction amplifies the defect information of the defective motif. Together with its variance, an energy-variance space is further defined where decision boundaries are drawn for classifying defective and defect-free motifs. As the 16 wallpaper groups of patterned fabric can be transformed into three major groups, the proposed method is evaluated over these three major groups, from which 160 defect-free lattices samples are used for defining the decision boundaries, with 140 defect-free and 113 defective samples used for testing. An overall detection success rate of 93.32% is achieved for the proposed method. No other generalized approach can achieve this success rate has been reported before, and hence this result outperforms all other previously published approaches.

TEXEMS: Texture Exemplars for Defect Detection on Random Textured Surfaces

We present an approach to detecting and localizing defects in random color textures which requires only a few defect free samples for unsupervised training. It is assumed that each image is generated by a superposition of various-size image patches with added variations at each pixel position. These image patches and their corresponding variances are referred to here as textural exemplars or texems. Mixture models are applied to obtain the texems using multiscale analysis to reduce the computational costs. Novelty detection on color texture surfaces is performed by examining the same-source similarity based on the data likelihood in multiscale, followed by logical processes to combine the defect candidates to localize defects. The proposed method is compared against a Gabor filter bank-based novelty detection method. Also, we compare different texem generalization schemes for defect detection in terms of accuracy and efficiency.