Historical Forces Research Articles

Research on the influence of impact damage on force identification for composite material

The invisible damage caused by low-velocity impacts are safety threats to engineering structures. Thus, impact force identification is crucial in the context of composite structures for both structure health monitoring (SHM) and composite structure design. This paper investigates the process of identifying impacts on composite structures subjected to low-velocity impact. Considering the damage evolution in the composite structure during impact, this paper explores the influence of impact damage on the accuracy of force identification. Impact experiments on carbon fiber reinforced polymer (CFRP) laminates were conducted to obtain impact force peaks and displacement responses. Furthermore, a validated finite element model (FEM) is established for more elaborate analysis on the mechanism. The findings reveal that the structural damage can lead to significant deviations in force identification if the damage is not considered. Finally, a neural network is employed to predict the force history taking impact damage into consideration. This research provides a reference for the composite structures design and health monitoring of engineering structures considering impact damage.

Experimental and numerical study on the flexural properties of RC beams with different CFRP-strengthened schemes

This study conducted a four-point bending experiment investigation on the flexural performances of the RC beams strengthened with various CFRP schemes. Four beams were employed, i.e., the ordinary RC beam (L0), the RC beam bonded with CFRP sheet (L1-C), the CFRP U-wrapped RC beam (L2-U), and the RC beam using CFRP rivets (L3-A). Test results highlighted the obvious improvement in the flexural performances of CFRP-strengthened beams in terms of enhancing load-carrying capacities and limiting overall deformations compared to beam L0. In addition, end anchorage systems, including CFRP U-hoop and CFRP rivets, changed the failure mode, restricted crack propagation, and mitigated the bottom CFRP sheet debonding effectively. The ultimate loads of beams L1-C, L2-U, and L3-A were 27.4 %, 36.4 %, and 41.6 % higher than beam L0, respectively, indicating that CFRP rivets performed the best in improving the beams' flexural properties. Finite element analysis was developed to simulate the bending experiment process. The numerical results comply well with the experiments in terms of the crack distribution pattern and bending force history. Then, parametric studies for the design suggestions with the use of the modes reveal that the implementation of the CFRP rivet with a depth of 80 mm and a diameter of 10 mm seems to be an ideal optimization plan for the beams herein.

Both‐Sideology Endangers Democracy and Social Science

AbstractIn social psychology these days it is commonplace to read or hear that liberal‐leftists and conservative‐rightists are every bit as “moral”; prejudiced and intolerant; susceptible to misinformation, “fake news,” and conspiratorial thinking; lax about upholding democratic standards; and prone to terrorism and political violence. Upon careful inspection, however, I conclude that every one of these claims is false or misleading. Liberal‐leftists in the United States and elsewhere are demonstrably more committed than conservative‐rightists to humanistic‐egalitarian values, deliberative reasoning, and adherence to democratic norms. In Western societies, acts of authoritarian aggression, hate crimes, and political violence are overwhelmingly more likely to come from the right than the left. As a witness to Nazi atrocities, Kurt Lewin deeply understood the role of historical, economic, and political forces in human lives and the interdependence between democracy and social science. He rejected moral relativism and what I call “both‐sideology” and offered a sophisticated critique of anti‐democratic tendencies. There are perfectly understandable reasons why people—especially academics and journalists—would be tempted to draw parallels between the left and right, and indeed there are many similarities as well as dissimilarities between liberal‐leftists and conservative‐rightists. However, the uncritical adoption of both‐sideology threatens liberal democracy itself and, with it, the only social science worth having. What we—as citizens and social scientists—need now is a renewal and revitalization of Lewin's critical‐emancipatory legacy before it is too late.

Influence of thermal history and consolidation force on wedge peel strength of CF/PEEK laminates manufactured by laser‐radiated in‐situ consolidation

AbstractProcessing parameters during the laser‐radiated in‐situ manufacturing process change the thermal history of the thermoplastic composite, which affects porosity and fiber‐resin interfacial bonding quality, and hence the wedge peel strength of the laminate. The effect of different laser powers and consolidation forces on the wedge peel strength of the specimens was investigated. Due to the fiber‐rich area on the tape surface during the laser heating phase as well as the insufficient consolidation force and consolidation length during the consolidation phase, the wedge peel strength decreased due to increased porosity and weak fiber‐resin bonding at the interlayer bonding interface. A conformable consolidation roller of lower hardness was used to improve the wedge peel strength of the laminates, which reduced the initial temperature of the cooling phase, thus inhibiting the void rebound and increasing the bonding strength at the fiber‐resin interface. The cross‐section and peeling surface were characterized by optical microscope and scanning electron microscope. The wedge peel strength of the laminates, with reduced voids and increased interfacial bonding strength between the fibers and the resin, is improved.Highlights Mechanism of void formation and evolution in different phases of laser‐radiated in‐situ consolidated laminate. Effect of consolidation roller hardness and deformation on wedge peel strength.

Quantitative matching of forensic evidence fragments using fracture surface topography and statistical learning

The complex jagged trajectory of fractured surfaces of two pieces of forensic evidence is used to recognize a “match” by using comparative microscopy and tactile pattern analysis. The material intrinsic properties and microstructures, as well as the exposure history of external forces on a fragment of forensic evidence have the premise of uniqueness at a relevant microscopic length scale (about 2–3 grains for cleavage fracture), wherein the statistics of the fracture surface become non-self-affine. We utilize these unique features to quantitatively describe the microscopic aspects of fracture surfaces for forensic comparisons, employing spectral analysis of the topography mapped by three-dimensional microscopy. Multivariate statistical learning tools are used to classify articles and result in near-perfect identification of a “match” and “non-match” among candidate forensic specimens. The framework has the potential for forensic application across a broad range of fractured materials and toolmarks, of diverse texture and mechanical properties.

Drag force on an accelerating flat plate at low Reynolds numbers

The accelerating flat plate is a useful model for studying the drag-based flapping flight (where drag is used to provide the weight-supporting force or thrust). Previous studies have mainly focused on the high Reynolds number (Re) regime pertaining to the flight of relatively large insects and birds. In this study, we numerically investigate the unsteady drag and flows of a uniformly accelerating flat plate at low Re that is typical of miniature insect flight (Re = 10–40). The following is shown. Unlike high-Re cases where the acceleration effect on drag is insensitive to Re, at low Re, the effect exhibits a strong dependence on Re: As Re decreases below 100, the acceleration effect increases rapidly, becoming 33%–56% greater than that of high-Re cases in the Re range of 10–40, before gradually decreasing. A simple model that consists of the quasi-steady, added-mass, and history force terms is proposed for drag at low Re. The scalings of the quasi-steady and added-mass force terms are well known; we find that the history force term scales approximately with the square root of the acceleration and velocity. The above result that relatively large drag is produced by the accelerating wing at Re = 10–40 is especially interesting and might explain why miniature insects fly in this Re range.

Anti-progressive collapse performance and design method of novel T-stub connections

To address the insufficient anti-collapse capacity of T-stub connections due to premature failure, this study proposes a novel T-stub connection (NTC) by adding four V-shaped laminated plates. Monotonic loading tests are conducted on the T-stub web and V-shaped laminated plate to analyze the influence of geometric parameters on their deformation and load-bearing capacity. The working mechanism of NTC is investigated through the validated numerical models by analyzing the failure mode, impact force history, deformation pattern, internal force development, and energy dissipation. The research results indicate that, compared to the T-stub connection, the NTC exhibits two-phase failure characteristics, which begin with the fracture of the bolt-hole in the T-stub web, followed by the gradual straightening and eventual fracture of the V-shaped laminated plates. NTC undergoes three stages under impact loads: peak, oscillation, and platform stages. The addition of V-shaped laminated plates enhances the ductility of NTC by 93 %−130 % and its energy dissipation capacity by 189 %−235 %. This significant enhancement in deformation and energy dissipation capabilities can be attributed to the addition of the V-shaped laminated plates. The deformation and bearing capacity calculation formulas for both the T-stub web and V-shaped laminated plate are provided. Additionally, a design method for NTC is proposed based on theoretical analysis, and its rationality is verified through numerical examples involving three different sets of beam and column sections.

From Waithood to Precariat: Unveiling the Unique Plight of the Sanhe Gods

In the realm of youth studies, the spotlight has often been cast upon the middle-class demographics and their contributions to internet culture, leaving a substantial portion of the youth populationthe lower-class youthlargely in the shadows. Among this overlooked demographic, the Sanhe gods stand out as a particularly neglected group. Despite their significant presence, having burgeoned in the early 2010s, it was not until the release of NHKs 2018 documentary Sanhe Talent Market: The Young People of China Earning 1500 Yen Daily that the academic world turned its gaze towards them for a thorough and systematic examination. This research paper aims to shed light on the unique circumstances surrounding the rise and current situation of the Sanhe gods. Through a qualitative analysis that incorporates anthropological studies by Chinese scholars and scrutinizes the digital footprints of the Sanhe gods across various internet platforms, this study seeks to unravel the complex tapestry of their existence. This study's findings underscore the Sanhe gods distinctiveness as a phenomenon deeply rooted in the socio-economic and cultural fabric of China, shaped by historical forces unique to the Chinese experience.

Aerosol-Induced Changes in Atmospheric and Oceanic Heat Transports in the CESM2 Large Ensemble

Abstract The total poleward energy transport (PET) is set by the top of atmosphere radiation flux, and is therefore sensitive to any process which can alter those fluxes, particularly in the shortwave. One example is the direct and indirect effects of anthropogenic aerosols, which increase the local reflection of solar radiation back to space. The historic emission of sulphur dioxide, which peaked in the northern midlatitudes during the 1980s, has been proposed as a primary contributor to historic anomalies in cross-equatorial energy transport, as well as related processes such as a shift in the tropical rainband. In this study, we analyze simulations from the CESM2 large ensemble and single-forcing projects to better understand the forced response of PET to historical forcings. First, analysis of the single-forcing project reveals that the position of the ITCZ responds in a non-linear manner to greenhouse gas forcing in CESM2. This type of non-linearity has been found previously in the context of the aerosol-only simulations in the CESM2 single-forcing project, but may be the first identification of a similar effect in the greenhouse gas-only simulations. Second, through analysis of the full CESM2 large ensemble simulations, we find that anomalous heat transport occurred in both the atmosphere (through the mean meridional circulation and atmospheric eddies) and in the oceans (through the Atlantic and Indo-Pacific sectors) due to a variety of related processes including the Hadley cells, the midlatitude storm tracks, the Atlantic Meridional Overturning Circulation (AMOC), and the Pacific wind-driven subtropical gyre.

Converged ensemble simulations of climate: possible trends in total solar irradiance cannot explain global warming alone

We address the hypothetical question of whether an increasing total solar irradiance (TSI) trend, without anthropogenic contributions, could be sufficient to explain the ongoing global warming. To this end, the intermediate-complexity climate model PlaSim is used. To consider the total internal variability, we present a set of ensemble simulations, with different forcing histories in TSI and CO2 concentration, that have converged sufficiently tightly to the relevant probability distributions to provide a satisfactory bound on any spurious trend possibly arising from a sampling bias; similar bounds on any other unforced contributions to ensemble mean trends are also estimated. A key point is the consideration, among the forcing histories, the steepest increasing trend in TSI that is still consistent with observations according to a recent study; thereby, we essentially revisit corresponding TSI reconstructions, more than 20 years after their last modeling-based evaluation, by improving the analysis through taking care of all possible sources of error or uncertainty and incorporating data that have become available since then. Without any change in CO2 concentration, our TSI trend (i.e., and upper bound on actual TSI trends) is found to be insufficient to produce outcomes compatible with the observational record in global mean surface temperature (GMST) with a nonnegligible probability. We formalize our statement for quantifiers of GMST trends through evaluating their distributions over the ensemble, and we speculate that the hypothesis about the exclusive role of an increasing TSI remains implausible even beyond our particular model setup. At the same time, if we consider a constant TSI, and the observational record in CO2 concentration is applied as forcing, the simulation results and the recorded GMST match well. While we currently need to leave the question of a precise attribution open, we conclude by pointing out that an attribution of the ongoing global warming to an increasing TSI alone could be made plausible only if a bias in the set of land-based instrumental temperature measurements were increasing more rapidly than commonly estimated; an assessment of the latter possibility is out of the scope of our study, as well as addressing solar forcing mechanisms beyond the effect of TSI.

Settling velocity characteristics of inertial particles in turbulent and wave-induced environments

In the present study, a theoretical model is proposed to calculate the settling velocity of solid particles in turbulence generated by both oscillatory and nearly horizontal flow motions. In contrast to other previous models that typically compartmentalize two flow conditions in their studies, this study takes a more comprehensive approach by considering the combined effects of both conditions. Taking into account the influence of drag nonlinearity, virtual mass and Basset history forces, the new theoretical model is formulated. The proposed model is obtained by solving the particle motion in fluid flow under some reasonable assumptions. Accordingly, we obtain a new dimensionless term to better take into account the effect of turbulence anisotropy on the settling velocity and the role of the sediment damping coefficient. Application of this term for other conditions is discussed in the paper. The present model shows satisfactory agreement with a wide range of experimental and numerical data and with different flow conditions found in the existing literature. These data include homogeneous isotropic turbulence with high resolution direct numerical simulations (DNS), turbulent open channel and vertical oscillation.

Observation-inferred resilience loss of the Amazon rainforest possibly due to internal climate variability

Abstract. Recent observation-based studies suggest that the Amazon rainforest has lost substantial resilience since 1990, indicating that the forest might undergo a critical transition in the near future due to global warming and deforestation. The idea is to use trends in a lag-1 auto-correlation of leaf density as an early-warning signal of an imminent critical threshold for rainforest dieback. Here we test whether the observed change in auto-correlations could arise from internal variability using historical and control simulations of nine sixth-generation Earth system model ensembles (Phase 6 of the Coupled Model Intercomparison Project, CMIP6). We quantify trends in the leaf area index auto-correlation from both models and satellite-observed vegetation optical depth from 1990 to 2017. Four models reproduce the observed trend with at least one historical realization whereby the observations lie at the upper limit of model variability. Three out of these four models exhibit similar behavior in control runs, suggesting that historical forcing is not necessary for simulating the observed trends. Furthermore, we do not observe a critical transition in any future runs under the strongest greenhouse gas emission scenario (SSP5-8.5) until 2100 in the four models that best reproduce the past observed trends. Hence, the currently observed trends could be caused simply by internal variability and, unless the data records are extended, have limited applicability as an early-warning signal. Our results suggest that the current rapid decline in the Amazon rainforest coverage is not foremost caused by global warming.

“Making America Gothic Again: Reading Alexis de Tocqueville’s Democracy in America Today”

Few historical phenomena seem less gothic than democracy, an ideal that is virtually always figured in terms of rational enlightenment and transparency, all of which made the January 6th insurrection in Washington especially unsettling: an interruption, not just of the important business of the day but of the most fundamental progressivist narratives of western civilization. But there have been other, more ominous accounts of democracy that would have figured these events more as a culmination than an interruption of the larger historical forces at work. Writing in the aftermath of the insurrection, this paper returns to Alexis de Tocqueville’s warning in Democracy in America that however precious, democracy was not the antithesis of despotism but an historically specific set of conditions that lent themselves to new, more insidious forms of despotism which would “degrade men without tormenting them.” Confronted with the spectre of this unprecedented form of oppression, Tocqueville warned in classic gothic terms that its greatest threat may have been its obscurity: “the old words of despotism and of tyranny do not work. The thing is new, so I must try to define it since I cannot name it.” It was, by all measures, a classic gothic tale: democracy as the basis for rather than safeguard against unprecedented and even unnameable forms of tyranny. This paper asks how Tocqueville’s warning can better understand our own highly polarized political situation today.

Amplified warming of North American cold extremes linked to human-induced changes in temperature variability

How global warming is impacting winter cold extremes is uncertain. Previous work has found decreasing winter temperature variability over North America which suggests a reduction in frequency and intensity of cold extremes relative to mean changes. However, others argue that cold air outbreaks are becoming more likely because of Arctic-induced changes in atmospheric circulation. Here we show that cold extremes over North America have warmed substantially faster than the winter mean temperature since 1980. This amplified warming is linked to both decreasing variance and changes in higher moments of the temperature distributions. Climate model simulations with historical forcings robustly capture the observed trends in extremes and variability. A pattern-based detection and attribution analysis shows that the changes in variability are detectable in observations and can be attributed to human influence. Our results highlight that human emissions are warming North American extreme cold temperatures beyond only shifting the winter mean temperature.

Punctuated Land: An Exploration of Conflict Through Photographic Practice

Punctuated Land (2019-2023) is a practice-led research project that, through photography, explores the enduring legacies of conflict and the historical and political forces that enable and perpetuate its normalization. Recurring visits to Israel/Palestine, tracing Israel’s de facto borders, and spending time in the occupied territories of the West Bank, were methods of observing how conflict gets inscribed on the verges and in the overlooked; including trees and other natural entities. This paper examines how living in ongoing conflict filters into the ground and into language, and how this informs how we view and interpret images. Traces and their photographic representation become the means to make visible the impact of maintaining dominance over the land. Practices of control and discrimination that appear in the landscape are reflected in the use of language, the interpretation of local laws, and the exercise of power over access and restrictions. While the mechanisms of violence and occupation promote a vision of this land as desolate and barren, this photographic project explores poetic and subtle visual methods to capture the traces of human presence that highlight the multiplicity of narratives and the entangled coexistence of collective memories.

How God Became a Lawgiver

The Torah is God’s law. This biblical concept is so prominent and is considered so self-evident that it has hardly been perceived as a historical problem until now. Traditionally, it was considered to be a basic element of the Bible within its historical context. But in fact, it represents an innovation in the ancient Near East, and for this very reason it should be investigated historically: In the ancient world, kings, not deities, were lawgivers. Only the legal tradition of ancient Israel developed the idea that God himself formulated laws and passed them on to his people. In the Torah, Moses plays a prominent role in this mediation. Divine laws then became a central element of religion in Judaism, Christianity, and Islam, but what historical circumstances and factors gave rise to them? The loss of kingship in Israel might have provided a major impact, but in addition to political and socio-historical developments, fundamental transformations in ancient Israel’s intellectual history must also be considered, which could have led to the formation of the idea of God as a lawgiver. Due to new insights into the historical emergence of the Torah, which research has developed in recent decades, but also due to new findings on the legal tradition of the ancient Near East, there is both the possibility and the need for reconstructing the historical forces and factors that made the Torah God’s law.

Reconstructing identities among Santhal: An anthropological perspective

This study of evolving identities is based on instrumental approach in a way that present identities are the product of historical forces and situations as the culture and society of Santhal from Haldibari Rural Municipality have always been in the form of evolution and acceptance of changing realities. It explains the changes seen in the origin, shifting nature, and their agentive space with resistance which has helped to create new space in their own life. This research is in quest of the ways of evolution of Santhal identities and their transforming relations due to various causes. It has uncovered Santhal of their ‘being’ and their subjective experiences as Santhal in the more significant eastern part of Tarai Nepal, particularly in Haldibari Rural Municipality.

Impact force identification for composite structures using adaptive wavelet-regularised deconvolution

Impact force identification (IFI) through deconvolution methods from measured structural responses poses a challenge due to the ill-posed nature of the inversion problem. Regularisation techniques, such as Tikhonov, sparse, and wavelet regularisation, offer potential solutions to mitigate the ill-posedness. However, determining suitable regularisation parameters is time-consuming. This study presents an adaptive wavelet-regularised time-domain deconvolution method for efficient IFI, based on wavelet transform and multi-resolution analysis. By analysing impact sensor signals using wavelets, adaptive impact windows covering the entire impact duration are generated, reducing signal length for deconvolution. Multi-resolution analysis of sensor signals enables identification of wavelet bases for the multi-resolution representation of impact force history. Regularisation is achieved by filtering out insignificant wavelet bases based on their energy contributions. Validation is performed through experiments involving small-mass hammer and large-mass drop tower impacts, comparing against various deconvolution methods. Results demonstrate the superior computational efficiency and comparable accuracy of the proposed adaptive method in IFI across different time windows. Notably, accurate force deconvolution for large-mass impacts confirms the effectiveness of the deconvolution methods for IFI, particularly when the structure undergoes significant local deformation.

Transient behavior of a plate partially immersed in the fluid subjected to impact loadings: Theoretical analysis and experimental measurements

This study aimed to investigate the transient behavior of a rectangular plate partially in contact with fluid subjected to a dynamic external force. To this purpose, a theoretical model was developed to analyze vibration characteristics and transient wave propagation. Based on superposition method, the dry mode shapes and natural frequencies of the plate under vacuum could be obtained. The dry mode shapes were treated as the fundamental function to construct the wet mode that describes the vibration behavior of the fluid-plate coupled system. The velocity potential and fluid pressure within a finite tank due to the plate deflection were derived using an equation governing the incompressible fluid. Based on the relationship between dry mode shape and wet mode shape, the fluid-plate coupled system's wet mode shape and resonant frequency could be determined from the frequency response function. Applying the normal mode method, the transient displacement of plate and fluid pressure can be obtained by solving a system of non-homogeneous differential equations. The theoretical predictions were verified by finite element method (FEM) and experimental measurements. Experiments were conducted using piezoelectric film sensors (polyvinylidene fluoride, PVDF) to measure the force history induced by a steel ball impact to quantitatively analyze the transient response. The comparison results proved that the theoretical predictions and experiments were in good agreement, including the transient responses of the displacement and in-plane strain of a plate partially submerged in the fluid. The results indicate that changes in water depth can induce resonance frequency shifts and wet mode shape distortions, which also illustrate that the vibrational properties of wet modes affect transient behavior. The proposed transient solution demonstrates an analytical approach that connects the physical significance of the dynamic behavior of the fluid-plate coupled system in time and frequency domains; it provides a connection between the transient behaviors and vibration characteristics.

Out-of-plane impact behavior and post-impact damage evaluation of GFRP bar-reinforced concrete shear walls in fire

Fiber-reinforced polymers (FRP) have been a prospective material in engineering. However, the attenuation of FRP bar-reinforced concrete members in fire is unclear. This paper studies the impact resistance of glass fiber-reinforced polymer bar-reinforced concrete (GFRP-RC) shear walls under high temperatures. Considering the impacts of strain rate enhancement and high temperature softening on GFRP bars and concrete, a numerical model with finite elements in three dimensions was created. To verify the model, three cases were simulated and compared with the test records, including the seismic performance of FRP-RC shear walls under axial compression, the seismic behavior of reinforced concrete (RC) shear walls under high temperatures, and RC shear walls' impact response. Based on the calibrated numerical model, the displacement, impact force, reaction force, failure mode, energy distribution, internal force and the residual shear bearing capacity of GFRP-RC shear wall subjected to impact under different fire times were analyzed. The influence of fire time on the failure mechanism of GFRP-RC shear walls was studied. Taking the mid-span displacement as the damage index, the evaluation criteria for the four damage levels were determined. The findings indicate that the type of reinforcement has little effect on the shape of impact force, reaction force and displacement time history curve. The peak values of impact force and reaction force of RC walls are larger than those of GFRP-RC shear walls, while the former has smaller peak displacements and residual displacements. The damage of shear walls becomes more severe as the fire time increases, as does the displacement. Also, the impact force, reaction force, shear force and bending moment decrease gradually. The energy absorbed by shear walls is primarily dissipated by concrete, the part by GFRP bars accounting for a small proportion. The post-impact residual bearing capacity of GFRP-RC shear walls is linearly related to the mid-span displacement under impact loads, primarily influenced by high-temperature exposure.