This study investigates the effect of environmental, social, and governance (ESG) activities and their disclosure on firm value. We find that ESG strengths increase firm value and that weaknesses ...decrease it. ESG disclosure, per se, decreases valuation. But more importantly, we find that disclosure plays a crucial moderating role by mitigating the negative effect of weaknesses and attenuating the positive effect of strengths.
An experimental study was conducted to investigate anisotropy effects on tensile properties of two short glass fiber reinforced thermoplastics. Tensile tests were performed in various mold flow ...directions and with two thicknesses. A shell–core morphology resulting from orientation distribution of fibers influenced the degree of anisotropy. Tensile strength and elastic modulus nonlinearly decreased with specimen angle and Tsai–Hill criterion was found to correlate variation of these properties with the fiber orientation. Variation of tensile toughness with fiber orientation and strain rate was evaluated and mechanisms of failure were identified based on fracture surface microscopic analysis and crack propagation paths. Fiber length, diameter, and orientation distribution mathematical models were also used along with analytical approaches to predict tensile strength and elastic modulus form tensile properties of constituent materials. Laminate analogy and modified Tsai–Hill criteria provided satisfactory predictions of elastic modulus and tensile strength, respectively.
This paper develops a valuation model of the firm that provides for the expenditure of corporate resources in support of community, social or environmental causes. We show that under certain ...circumstances CSR expenditures create value for the firm. We also test our model by simulations and confirm that, at least under some conditions, CSR does pay off in the form of value creation.
Additive manufacturing (AM) has provided an opportunity for fabricating complex parts. Fabricating these parts without defects is currently a challenge. Therefore, understanding AM defects is ...fundamental to the structural integrity of load carrying components, failure analysis, and defect-based modeling of mechanical performance. This work investigates defect content of metal AM specimens and correlations between defect characteristics (size, sphericity/circularity, aspect ratio) using 2D and 3D defect characterization techniques. Distributions of defect characteristics based on location throughout AM specimens were analyzed and the variabilities of defect characteristics within these specimens were studied. Laser-Based Power Bed Fusion (L-PBF) specimens manufactured with different metals, different AM machines and built directions, different surface conditions, and different thicknesses were evaluated. Significant variability in defect characteristics based on location, especially in as-built surface specimens was observed. Well-optimized process parameters and post-processing reduced the overall volume fraction of defects, and the specified variabilities, and resulted in a more random dispersion of defects around the specimens. 2D and 3D defect analysis showed similar trends regarding correlations between defect characteristics and provided complementary information about the actual defect content based on their resolution.
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•Variability analysis of defect distributions of L-PBF specimens showed critical defects concentrated in specific locations.•Apt process parameters, surface machining, and Hot Isostatic Pressing improved defect content repeatability in specimens.•Hot Isostatic Pressing increased defects aspect ratio and decreased their size, therefore reduced directionality of defects.•Lack of Fusion defects decreased 2D analysis results reliability and increased the need for 3D defect analysis.
•Effect of hot isostatic pressing (HIP) on multiaxial fatigue of AM Ti-6Al-4V.•Build orientation effect on multiaxial fatigue of AM Ti-6Al-4V.•Surface roughness effect on multiaxial fatigue of AM ...Ti-6Al-4V.•Damage mechanism and effect of defects in multiaxial fatigue of AM Ti-6Al-4V.
Additive manufacturing (AM) technology has gained significant attention in recent years due to several important advantages. However, design of critical load carrying parts using this technique is still at its infancy, partly due to the inferior performance and lack of sufficient understanding of cyclic deformation and fatigue behaviors of AM metals as compared to their wrought counterparts. Similar to most other components in different industries, AM parts typically undergo cyclic loadings through their service life; therefore, fatigue performance is a key performance criterion. In addition, due to common presence of multiaxial stress states at fatigue critical locations, multiaxial fatigue is of special interest. In this study, thin-walled tubular specimens made of Ti-6Al-4V alloy fabricated with powder bed fusion (PBF) process were used to investigate their cyclic deformation and fatigue behaviors. The main focus of this study was on the effect of hot isostatic pressing (HIP) on fatigue performance under uniaxial, torsion, combined in-phase, and 90° out-of-phase axial-torsion loads. To study build orientation effect, both vertically built and diagonally built (at 45°) specimens were included. However, no substantial difference on the fatigue behavior of vertical and 45° built specimens was observed. Although the majority of specimens had a machined surface, some torsional tests with as-built surface were also included to evaluate surface roughness effect. It was found that even after HIP treatment, the rough surface is the dominant factor in shortening the fatigue life. In addition, to evaluate the effectiveness of the HIP treatment, torsion fatigue performance of the HIPed specimens were compared to torsion fatigue performance of annealed AM specimens, as well as to the multiaxial fatigue behavior of the conventional wrought material. Fatigue failure mechanism of the HIPed material was shear, similar to the wrought material, and fatigue performance was found to be similar to the wrought alloy. Fatigue test results were correlated well using a shear-based critical plane parameter approach, also similar to the wrought material. Comparison of multiaxial fatigue data in this study and a similar previous study by the authors indicates that fabrication machine-to-machine and the associated build parameter differences can result in substantial differences in the observed defect size and population, resulting in different failure mechanisms and subsequently different fatigue performance.
A brief overview of some important issues in multiaxial fatigue and life estimation is presented. These include damage mechanisms and damage quantification parameters, material constitutive response ...and non-proportional hardening, cycle counting and damage accumulation in variable amplitude loading, and mixed-mode crack growth. It is shown that capturing the correct damage mechanism is essential to develop a proper damage quantification parameter for robust multiaxial fatigue life estimation. Additional cyclic hardening of some materials under non-proportional multiaxial loading and its dependence on the load path as well as material microstructure is also discussed. It is argued that critical plane damage models with both stress and strain terms are most appropriate since they can reflect the material constitutive response under non-proportional loading. Importance of a proper cycle counting method to identify cycles in a variable amplitude load history, and capability of the linear cumulative damage rule to sum damage from the counted cycles are also discussed. As mixed-mode crack growth can constitute a significant portion of the total fatigue life, analysis of crack growth rates and correlations under combined stresses is presented. Several models as well as some simple approximations in capturing the aforementioned effects in multiaxial fatigue life estimations are also described. The approximation models include an estimation model for obtaining material non-proportional cyclic hardening coefficient, and a simple multiaxial fatigue life estimation model for steels based on hardness as the only required material property.
The primary goal of this study was to investigate the monotonic tensile behavior of high-density polyethylene (HDPE) in its virgin, regrind, and laminated forms. HDPE is the most commonly used ...polymer in many industries. A variety of tensile tests were performed using plate-type specimens made of rectangular plaques. Several factors can affect the tensile behavior such as thickness, processing technique, temperature, and strain rate. Testing temperatures were chosen at −40, 23 (room temperature, RT), 53, and 82 °C to investigate temperature effect. Tensile properties, including elastic modulus, yield strength, and ultimate tensile strength, were obtained for all conditions. Tensile properties significantly reduced by increasing temperature while elastic modulus and ultimate tensile strength linearly increased at higher strain rates. A significant effect of thickness on tensile properties was observed for injection molding specimens at 23 °C, but no thickness effect was observed for compression molded specimens at either 23 or 82 °C. The aforementioned effects and discussion of their influence on tensile properties are presented in this paper. Polynomial relations for tensile properties, including elastic modulus, yield strength, and ultimate tensile strength, were developed as functions of temperature and strain rate. Such relations can be used to estimate tensile properties of HDPE as a function of temperature and/or strain rate for application in designing parts with this material.
Creep behavior of high-density polyethylene (HDPE) was investigated. HDPE has many engineering applications in different industries such as piping systems, cable and wiring, automotive parts, storage ...containers, and biomedical implants. The temperatures chosen were 23, 53, and 82 °C based on the service temperature range for application in design of automotive fuel tanks. Creep strength decreased and creep strain as well as creep strain rate increased by increasing temperature. The Larson-Miller parameter widely used for metallic materials was able to correlate time to rupture, stress, and temperature data of HDPE. The Monkman-Grant relation was successfully used to correlate minimum creep rate and time to rupture. The Findley power law and time-stress superposition principle (TSS) were used to represent nonlinear viscoelastic creep curves. Some longer-term creep tests were also conducted at room temperature to evaluate the accuracy of extrapolation of the short-term creep test results to longer creep life predictions. The models used based on the data presented can be used in the design of parts and components made of HDPE where creep failure may be a concern.
•Experimental characterization of creep behavior of high-density polyethylene (HDPE).•Successful modeling of the creep rupture data with the Larson-Miller parameter.•Successful modeling of the minimum creep rate with the Monkman-Grant relation.•Representation of nonlinear viscoelastic creep curves with Findley power law and time-stress superposition principle (TSS).•Extrapolation of longer creep life predictions based on short-term creep data and experimental verification.
•Multiaxial fatigue of powder bed fusion additive manufactured (AM) Ti-6Al-4V.•Surface finish and heat treatment effects on multiaxial fatigue of AM Ti-6Al-4V.•Damage mechanism and effect of defects ...in multiaxial fatigue of AM Ti-6Al-4V.•Multiaxial fatigue behavior and failure mechanism of wrought Ti-6Al-4V.
Additive manufacturing (AM) technology has enabled efficient fabrication of parts with complex geometries and laser-based powder bed fusion (L-PBF) is one of the most commonly used AM fabrication process. In many applications, the loading condition of AM parts is multiaxial. Even under uniaxial loading conditions, due to the geometry complexity or interaction of residual stresses, the stress state may still be multiaxial. Therefore, an understanding of cyclic deformation and fatigue behaviors of AM materials under multiaxial stress states is critical to the expected performance of such parts. These behaviors were investigated in this study using thin-walled tubular specimens of Ti-6Al-4V alloy made of a common PBF process. To compare with the conventional material performance, wrought Ti-6Al-4V alloy was also investigated. The loadings considered included axial, torsion, in-phase axial-torsion, and 90° out-of-phase axial-torsion loads. The surface roughness effect was also studied by considering both the as-built and the machined and polished surface conditions of the AM specimens. The ductility of the AM material was found to be significantly lower than the wrought material due to the martensitic microstructure as well as the presence of defects. AM specimens had significantly shorter lives compared to the wrought specimens under all loading conditions and regardless of the surface finish. However, machining improved the fatigue performance of AM specimens. For all loading conditions brittle fracture of AM specimens was observed with cracking on maximum tensile plane, and ductile fracture of wrought specimens with shear cracking. Consequently, fatigue test results of the wrought material were correlated using a shear-based critical plane model, while the AM specimen test data were correlated based on the maximum principal stress criterion.
Abstract Background Neuroplasticity refers to the inherently dynamic biological capacity of the central nervous system (CNS) to undergo maturation, change structurally and functionally in response to ...experience and to adapt following injury. This malleability is achieved by modulating subsets of genetic, molecular and cellular mechanisms that influence the dynamics of synaptic connections and neural circuitry formation culminating in gain or loss of behavior or function. Neuroplasticity in the healthy developing brain exhibits a heterochronus cortex-specific developmental profile and is heightened during “critical and sensitive periods” of pre and postnatal brain development that enable the construction and consolidation of experience-dependent structural and functional brain connections. Purpose In this review, our primary goal is to highlight the essential role of neuroplasticity in brain development, and to draw attention to the complex relationship between different levels of the developing nervous system that are subjected to plasticity in health and disease. Another goal of this review is to explore the relationship between plasticity responses of the developing brain and how they are influenced by critical and sensitive periods of brain development. Finally, we aim to motivate researchers in the pediatric neuromodulation field to build on the current knowledge of normal and abnormal neuroplasticity, especially synaptic plasticity, and their dependence on “critical or sensitive periods” of neural development to inform the design, timing and sequencing of neuromodulatory interventions in order to enhance and optimize their translational applications in childhood disorders of the brain. Methods literature review. Results We discuss in details five patterns of neuroplasticity expressed by the developing brain: 1) developmental plasticity which is further classified into normal and impaired developmental plasticity as seen in syndromic autism spectrum disorders, 2) adaptive (experience-dependent) plasticity following intense motor skill training, 3) reactive plasticity to pre and post natal CNS injury or sensory deprivation, 4) excessive plasticity (loss of homeostatic regulation) as seen in dystonia and refractory epilepsy, 6) and finally, plasticity as the brain's “Achilles tendon” which induces brain vulnerability under certain conditions such as hypoxic ischemic encephalopathy and epileptic encephalopathy syndromes. We then explore the unique feature of “time-sensitive heightened plasticity responses” in the developing brain in the in the context of neuromodulation. Conclusion The different patterns of neuroplasticity and the unique feature of heightened plasticity during critical and sensitive periods are important concepts for researchers and clinicians in the field of pediatric neurology and neurodevelopmental disabilities. These concepts need to be examined systematically in the context of pediatric neuromodulation. We propose that critical and sensitive periods of brain development in health and disease can create “windows of opportunity” for neuromodulatory interventions that are not commonly seen in adult brain and probably augment plasticity responses and improve clinical outcomes.
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