Larger Loading Rate Research Articles

Cyclic degradation mechanisms of Al0.3CoCrFeNi high-entropy alloy under different loading rates

The effect of loading rate on the cyclic degradation behavior of Al0.3CoCrFeNi high-entropy alloy (HEA) was investigated through nanoindentation experiments and molecular dynamics simulations. The evolution of mechanical properties and microstructure characteristics under different loading rates, as well as the mechanisms of cyclic degradation, were revealed. It is found that the increase of the loading rate induces higher hardness and smaller nanoindentation depth of the Al0.3CoCrFeNi HEA, which gradually increases with the cyclic loading of nanoindentation, resulting in a larger difference in characteristic nanoindentation depth among different loading rates. What’s more, a larger loading rate is inclined for nanoindentation depth to reach a steady state. Slip lines and pile-ups are formed around the nanoindentation region at higher loading rates indicating the occurrence of a more localized plastic deformation, while an amorphous transformation occurs at different loading rates after cyclic nanoindentation. Cyclic loading results in the gradual accumulation of residual stress, nanoindentation depth and amorphous structures within the material, and a localized plastic deformation. In summary, cyclic degradation of the Al0.3CoCrFeNi HEA is featured by cyclic softening due to dislocation slipping and the accumulation of amorphous phases.

Anomalous Loading Rate Dependence of the Mechanical Properties of Metal-Organic Framework Crystals: Latent Heat Effects of the Pressure-Induced Local Phase Transition.

The loading rate dependence of the mechanical properties of metal-organic framework (MOF) crystals is key in determining their performance in many engineering applications, which, however, remains almost unexplored. Here, in situ nanoindentation experiments were conducted to investigate the impact of loading rate on mechanical properties of HKUST-1, a classic MOF. The Young's modulus and hardness of crystalline HKUST-1 are found to stay stable or decline with decreasing loading rate by creeping when the loading rate is below a particular speed, but they significantly decrease as the loading rate grows when it has higher magnitudes. Our molecular dynamics simulations indicate that the anomalous loading rate dependence of mechanical properties is attributed to the competition between the release and transfer of latent heat from the pressure-induced amorphous HKUST-1 because the increase in local temperature at large loading rates could induce the softening of HKUST-1 and the increase in the volume of transformed materials.

Strain rockburst evolution process under true triaxial condition with single face unloading due to tunnel excavation

Based on the technology of polycrystalline modelling (generating Voronoi polycrystal) and three-dimensional discrete element theory, a three-dimensional polycrystalline discrete element nonlinear dynamic and static coupled numerical analysis method was proposed. This method can accurately simulate the initiation and evolution entire process of strain rockburst. The three-dimensional Voronoi polycrystalline discrete element model considering the mineral composition was established. The rockburst simulation of heterogeneous granite under true triaxial single face unloading was carried out. The rockburst ejection failure characteristics, strength and deformation characteristics, acoustic emission characteristics of rock samples were analyzed, as well as the characteristics of rock fragments and the evolution law of kinetic energy. The inoculation and evolution entire process of strain rockburst during true triaxial single face unloading was studied. The research results show that the failure process of rockburst ejection can be divided into four stages, including: grains ejection, rock spalling into plates, rock shearing into fragments, and rock fragments ejection. The failure modes of rockburst are pluralistic, that is, rockburst pits caused by tension-shear failure and split cracks due to tensile failure near the unloading face, and shear cracks caused by shear failure away from the unloading face. The kinetic energy is released abruptly in the post-peak stage, and the kinetic energy suddenly increases from zero to a high value when elastic energy drops sharply. The dissipation energy of rockburst fragments mainly includes shear dissipation energy and tension dissipation energy; among them, the shear dissipation energy accounts for 99.66 %. The primary conditions for rockburst ejection failure are accumulating enough elastic strain energy and reaching a large loading rate in the tangential direction.

An Experimental Research on Surrounding Rock Unloading during Solid Coal Roadway Excavation

In order to further explore the deformation and failure essence of the deep coal body, based on the characteristics of surrounding rock stress adjustment before and after solid coal roadway excavation, an experiment of unloading confining pressure and loading axial pressure of the coal body was designed and conducted in this study. Based on test results, the failure mechanics and energy characteristics of the coal body were analyzed through experiments. Rapid unloading is considered a key factor contributing to lateral deformation and expansion failure, which exacerbates the deterioration of coal body and reduces the deformation energy storage capacity of coal. On the other hand, the larger loading rate tends to shorten the accumulation time of microcracks and cause damage to the coal body, resulting in strengthening the coal body and improving energy storage. Under the circumstance that the coal body is destroyed, the conversion rates of the internal deformation energy and dissipated energy are more significantly affected by unloading rate. The increasing unloading rate and rapid decreases in the conversion rate of deformation energy make the coal body more vulnerable to damage. Under the same stress conditions, the excavation unloading is more likely to deform, destroy, or even throw the coal than the experiment unloading. In order to reduce or avoid the occurrence of deep roadway excavation accidents, the understanding of the excavation unloading including possible influencing factors and the monitoring of the surrounding rock stress and energy during the excavation disturbance should be strengthened. It can be used as the basis for studying the mechanism of deformation and failure of coal and rock and dynamic disasters in deep mines, as well as the prediction, early warning, prevention, and control of related dynamic disasters.

Application and Effect of Loading Rates on Coal Sample Failure

In order to evaluate the coal pillar stability in recovery of residual room pillars under different mining rates, this paper studies the influence of loading rate on the mechanical properties of the coal body. The uniaxial compression tests of coal samples in Yangcheng area at different loading rates were carried out with the MTS815 electrohydraulic servo rock mechanics test system. The stress‐strain curves and the evolution characteristics of AE signals were analyzed. At same time, the mechanism of damage and failure of specimens are also discussed. The results show the following. (1) With the increase in loading rate, the ultimate stress and ultimate strain of specimens decrease first and then increase. (2) Loading rate has a significant effect on the stability adjustment of specimens. With the decrease in loading rate, the earlier the stress adjustment is, the larger the adjustment range is, and the failure mode changes from shear failure to tensile failure. (3) In addition, when the loading rate increases, the AE evolves from continuous dense to discrete catastrophe, which indicates that the failure of the sample at a larger loading rate is sudden, which is not conducive to the maintenance of the stability of the coal pillar. (4) Finally, the failure mechanism of the specimen structure under different loading rates is obtained, and the improvement measures for the effect of mining velocity of working face on the stability of coal pillar are put forward. The results reveal the loading rate effect of mechanical properties of coal and provide a reference for controlling the stability of the residual coal pillar.

Effect of spherical indenter radius and loading rate on the kinetic nanoindentation creep behavior of La-based metallic glasses

Although the effect of the deformation field size on the mechanical strength of metallic glasses (MGs) has been investigated thoroughly, a few studies have investigated the effect of the deformation field size on the kinetic creep deformation behavior for these materials. This issue is addressed in the current work by investigating the nanoindentation creep kinetics of La-based MGs under the application of spherical indenters with two different tip radii and three different loading rates. The experimental data are fit to a viscoelastic model to extract the activation volume and relaxation time characteristics of the kinetic nanoindentation creep deformation of the samples. The results demonstrate that the nanoindentation creep kinetics are not only strongly dependent on the loading rate, but also vary significantly with the indenter tip radius. The deformation dynamics is interpreted by the stretched exponent β, indicating its relatively small value at a large loading rate along with a large indenter tip radius. Furthermore, the observed effect of the deformation field size can be attributed to an interplay between the deformation field under the spherical indenter and flow defects associated with the excess free volume, shear transition zone, or shear band embryo with an evolution that is essentially dependent on the loading rate. The current findings contribute to a fundamental understanding of the mechanism of shear softening during creep deformation in MGs.

Bioretention planter performance measured by lag and capture.

Bioretention flow-through planters manage stormwater with smaller space requirements or structural constraints associated with other forms of green infrastructure. This project monitored the hydrology of four bioretention planters at Stevens Institute of Technology to evaluate the system's ability to delay runoff and fully capture small rain events. The water depth in the outflow and the volumetric water content near the inflow were measured continuously over 15 months. Rainfall characteristics were documented from an on-site rain gauge. This monitoring determined the time from the start of a rain event to the onset of outflow from each planter, which was defined as the lag. The initial moisture deficit (difference between pre-event volumetric water content and maximum measured volumetric water content), approximate runoff volume, and approximate runoff volume in the first half hour were analysed to determine their effect on runoff capture and lag. During the monitoring period, 38% of observations did not produce measurable outflow. Logistic regression determined that the initial moisture deficit and approximate runoff volume were statistically significant in contributing to a fully captured storm. Despite the large hydraulic loading rate and concrete bottom, the planters demonstrate effective discharge lag, ranging from 5 to 1,841 min with a median of 77.5 min. Volumetric water content of the media and inlet runoff volume in the first half hour were significant in modelling the lag duration. These results represent a combination of controllable and uncontrollable aspects of green infrastructure: media design and rainfall.

Mechanical Model of a Hybrid Non-linear Viscoelastic Material Damping Device With Its Verifications

This paper proposes a new viscoelastic (VE) material damping device with hybrid nonlinear properties. Compared with traditional linear material dampers, the new nonlinear VE material damping device is characterized by its better energy dissipation and deformation capability. The series performance tests of the VE device are conducted, based on which the sources and variation law of material nonlinearities are analyzed. Five aspects of material nonlinearities are summarized, including the shape change of hysteresis loop caused by phase difference, the initial stiffness caused by large loading rate, the softening effect caused by high temperature and fatigue, and the softening and stiffening effect under large strain deformation. Then, a mechanic model for this device is proposed which considers multiple nonlinear effects of the material. For the verifications of the proposed mechanic model, a shaking table test on a steel frame equipped with the new VE devices is designed and performed. Based on the proposed mathematic mechanic model, the numerical mechanic model is implemented in the OpenSees software. The accuracy of the mechanic model is firstly verified by comparing the performance tests data with the simulation results. Then numerical model is also used to calculate the time history response of the shake table tested steel frame under earthquake loading. It is concluded that the mechanic model can well depict several nonlinear material behaviors of the new VE device, and the corresponding numerical model created in the open source calculation platform is reliable to be used to calculate nonlinear time history response of a structure equipped with the new VE material damping devices.

Livestock and Poultry Faeces Nitrogen Loading Rate and Its Potential Return to Farmland in China

To clearly analyze livestock and poultry faeces and the nitrogen loading rate of farmland in different provinces of China and their potential return to agricultural land, the changes of the output of various livestock and poultry faeces in China and the proportion of faeces from all types of livestock and poultry since 1978 were estimated in this paper based on statistical data and literature reviews using the pig manure equivalent (based on nitrogen) and the spatial distribution and pollution risk of livestock and the poultry faeces and nitrogen loading rates. Furthermore, the nitrogen return potential from animal faeces to farmland was analyzed and evaluated for different provinces of China in 2016. The results show that the pig manure equivalent (N) and total N from livestock and poultry faeces in China increases from 1978 to 2005 and is stable from 2005 to 2016. By 2016, the pig manure equivalent (N) and N were 366822.01×104 t and 2024.10×104 t, respectively, reflecting an increase by 105.78%. Approximately 94.03% to 98.34% of the faeces was from poultry, sheep, pigs, and cattle. The livestock and poultry faeces pig manure equivalent (N) and nutrient N were mainly distributed in North-Central China, especially in the Henan Province, accounting for 22.25% and 8.81% of the total in China, respectively, followed by the Sichuan Province. Based on the arable land, planting, and farmland areas, the pig faeces equivalent (N) and its N nutrient per unit area were calculated and the environmental risks were evaluated based on r values. Based on the arable land area, the southwestern and southeastern regions have large loading rates, while the northcentral region has a serious pollution risk of grade Ⅳ. Based on the planting area, the northwestern and southwestern regions have relatively large loading rates, while the northwestern and northcentral regions have pollution risks of grade Ⅲ. Based on the farmland area, the northcentral and southeastern regions have great loading rates and the northcentral region has a pollution risk of grade Ⅲ, Hunan has the largest loading rate, and Beijing, Shandong, and Henan have grade Ⅳ pollution risks. The livestock and poultry faeces pig manure equivalent (N) and amount of N nutrients returning to farmland in China are 113480.75×104 t and 626.15×104 t, respectively, equivalent to 3.07 t·hm-2 and 16.92 kg·hm-2, respectively, and the northcentral region has the largest rates with 8.27 t·hm-2 and 45.62 kg·hm-2, respectively. Based on 50% of the environmental capacity of faeces N, that is, 85 kg·hm-2, the N nutrient return can increase by 2520.21×104 t. The Heilongjiang Province has the greatest potential return, followed by the Sichuan Province.

Mechanical characterisation of brain tissue up to 35% strain at 1, 10, and 100/s using a custom-built micro-indentation apparatus.

Understanding the behaviour of soft tissues under large strains and high loading rates is crucial in the field of biomechanics in order to investigate tissue behaviour during pathological processes such as traumatic brain injury (TBI). It is, therefore, necessary to characterise the mechanical properties of such tissues under large strain and high strain rates that are similar to those experienced during injury. However, there is a dearth of large strain and high rate mechanical properties for brain tissue. This is likely driven by the lack of commercially available equipment to perform such tests and the difficulties associated with developing appropriate custom-built apparatus. Here, we address this problem by presenting a novel, custom-built micro-indentation apparatus that is capable of characterising the mechanical properties of brain tissue up to 35% at 100/s with a spatial resolution of 250 µm. Indentations were performed on the cortex and cerebellum of five-week-old mouse brains up to 35% strain at 1, 10, and 100/s. Three hyperelastic models were fitted to the experimental data that demonstrate the strong rate-dependency of the tissue. The neo-Hookean shear modulus for the cortex tissue was calculated to be 2.36 ± 0.46, 3.64 ± 0.48, and 8.98 ± 0.66 kPa (mean ± SD) for 1, 10, and 100/s, respectively. Similarly, the cerebellum shear modulus was calculated to be 1.12 ± 0.26, 1.58 ± 0.32, 3.10 ± 0.70 kPa for 1, 10, and 100/s, respectively. Student's t-tests were used to show statistically significant differences between the cortex and cerebellum at each strain rate. Furthermore, we discuss the apparent strain-softening effect in the 100/s force-displacement curves for both regions after approximately 30% strain.

Classification and fractal characteristics of coal rock fragments under uniaxial cyclic loading conditions

Rock burst is a serious geological hazard in deep underground mines affecting progress of mining operations. Although rock burst is a complex process, a distribution law of fractal characteristics can explain the rock failure mechanism. Using a servo-controlled testing system, uniaxial cyclic loading tests on coal rock specimens were conducted to investigate the fractal characteristics of the fragments under different loading rates. To comprehensively characterize the coal fragments of different sizes, samples were divided into four groups of different size: particles, fine, medium-size, and coarse fragments. The distribution of the fragments under uniaxial cyclic loading conditions was then investigated based on the theory of fractal geometry, and the relationships between fractal dimensions and loading rates. Under uniaxial cyclic loading and unloading conditions, most of the fragments are irregular wedges and bulks, exhibiting obvious shape characteristics. Under various loading rates, the length-quantity fractal dimensions of the coal fragments ranged from 0.74 to 1.44, the width-quantity fractal dimensions range from 0.44 to 1.65, and the thickness-cumulative mass fractal dimensions range from 1.0 to 1.33. The coal rock’s crushing size-mass fractal dimensions under different loading rates were 2.27, 2.30, 2.32, and 2.35, respectively. Under a small loading rate, the dimension-quantity fractal dimensions are relatively small, suggesting that the coal rock was less crushed, with large fragments differing greatly in length, width, and thickness. The results show that the coal rock fragments exhibit certain shape characteristics after the cyclic loading, like irregular shapes and wedges. Under a larger loading rate, the fragments showed greater fractal dimensions of both size and mass; the coal samples crushed more thoroughly with more uniform fragments in length, width, thickness and mass. The conclusions obtained in this study confirm the classification and fractal characteristics of coal rock fragments by uniaxial cyclic loading conditions in laboratory test and provide the basis for further study on the mechanism of rock burst. This study is helpful for us to make a thorough inquiry the danger degree of rock burst in coal mine by using fractal geometry, understand the effects of methane to coal and the evolution mechanism of cracks, and it can be applied to the research on occurrence mechanism and early warning of rock burst.

Dynamic behaviors of phase transforming cellular structures

In this work, the dynamic behaviors of phase transforming cellular structures (PTCS) consisted of sinusoidal beam with bi-stable configurations are studied. A nonlinear spring-bead model is developed, where the mechanical properties of the sinusoidal beam are described by a nonlinear spring and the mass is concentrated at the bead. Therefore, the PTCS are modeled as a chain of nonlinear spring-bead. Based on the nonlinear spring-bead model, the quasi-static and dynamic behaviors of PTCS are theoretically and numerically studied, which shows abundant dynamic behaviors depending on the loading rate and damping coefficient. For a 2-layered PTCS, there are four deformation patterns, that is the snap through deformation of the sinusoidal beams for relatively small loading rate and damping coefficient, the uniform deformation for relatively large damping coefficient, and the pulse deformation of the springs near bi-stable configurations for relatively large loading rate and small damping coefficient. While, for the multilayer PTCS, their dynamic behaviors are much more complicated due to the combined deformation of the multiple sinusoidal beams. However, the similar snap through and pulse deformation of the sinusoidal beams are also observed, respectively. To our knowledge, this work is the first time to systematically study the dynamic behaviors of PTCS.

Wastewater Treatment Plant Performance Inside Multi-Soil-Layering System

Wastewater effluent disposal is a challenge in Moroccan rural area. Wastewater treatment is the only suitable solution to overcome these environmental constraints. Technology such as Multi-Soil-Layering (MSL) system is one of the most appropriate solution for the treatment of wastewater for small communities in rural areas. The MSL system overcomes many of the deficiencies of conventional soil treatment systems such as large land requirement clogging and low Hydraulic Loading Rate (HLR). The MSL systems are composed of Soil Mixture Blocks (SMB) arranged in a brick-like pattern and surrounded by Permeable Layers (PL). To investigate the efficiency of MSL systems in relation to HLR differences and the fluctuations in the wastewater contamination levels, three MSL pilot plants were alimented continuously by domestic wastewater, were constructed in three 36×30×65 cm plastic boxes, with different HLR of 250, 500 and 1000 l/m2/day. The main removal rates of Biochemical Oxygen Demand (BOD5) and Chemical Oxygen Demand (COD) were higher at higher HLR. However, the kinetic rate constant of the MSL process implemented under Moroccan conditions is 130 d-1 at 25°C.

Integration of a continuum damage model for shale with the cutting plane algorithm

Summary The stability of integration is essential to numerical simulations especially when solving nonlinear problems. In this work, a continuum damage mechanics model proposed by the first author is implemented with an integration method named cutting plane algorithm (CPA) to improve the robustness of the simulation. This integration method is one type of return mapping algorithm that bypasses the need for computing the gradients. We compare the current integration method with the previous direct method, and the result shows that the cutting plane algorithm exhibits excellent performance under large loading rate conditions. To enhance accuracy of the new method, a control procedure is utilized in the implementation of the algorithm based on error analysis. Thereafter, the theory of poromechanics is utilized with the damage model to account for the effects of fluid diffusion. Laboratory tests simulated with finite element method illustrate distinct behaviors of shale with different loading rates and indicate the development of microcrack propagation under triaxial compression. Copyright © 2016 John Wiley & Sons, Ltd.

Structural Connections of Steel Building Frames under Extreme Loading

Resistance to progressive collapse under extreme loading is a measure of the structural robustness, and relies primarily on resistance of key elements, continuity between elements and ductility of elements and their connections. In case some hazards occur simultaneously or consecutively in a very short period of time, e.g. fire after explosion or impact, the capacity of the members and connections can be exceeded and this can initiate the progressive collapse of the structure. The paper presents the results of a research program that focused on the ultimate capacity of connection macro-components under large deformation demands and different loading rates. The specimens were extracted from extended end plate bolted beam-to-column connections with different strength and stiffness ratios to the beams.

Exploratory Investigation of Impact Loads During the Forward Handspring Vault.

The purpose of this study was to examine kinematic and kinetic differences in low and high intensity hand support impact loads during a forward handspring vault. A high-speed video camera (500 Hz) and two portable force platforms (500 Hz) were installed on the surface of the vault table. Two-dimensional analyses were conducted on 24 forward handspring vaults performed by 12 senior level, junior Olympic program female gymnasts (16.9 ±1.4 yr; body height 1.60 ±0.1 m; body mass 56.7 ±7.8 kg). Load intensities at impact with the vault table were classified as low (peak force < 0.8 × body weight) and high (peak force > 0.8 × body weight). These vaults were compared via crucial kinetic and kinematic variables using independent t-tests and Pearson correlations. Statistically significant (p < 0.001) differences were observed in peak force (t(24) = 4.75, ES = 3.37) and time to peak force (t(24) = 2.07, ES = 1.56). Statistically significant relationships between the loading rate and time to peak force were observed for high intensity loads. Peak force, time to peak force, and a shoulder angle at impact were identified as primary variables potentially involved in the determination of large repetitive loading rates on the forward handspring vault.

Mechanical Behavior of Polycrystalline Aluminum under Penetration with Extremely Large Loading Rates via Molecular Dynamics Simulation

In this study, polycrystalline aluminum nanoscale thin sheets are constructed by sputter deposition simulations with the molecular dynamics (MD) simulation. Subsequently, the penetration problem of a conical rigid projectile moving through the aluminum thin sheet is simulated by the MD technique. The MD simulations adopted the interatomic potential of a tight-binding type. During the deposition simulation, in order to include the ion-ion interactions, the pair-wise Moliere potential was adopted to model the interaction between working gas argon and deposited atoms. The as-deposited films did not show clear grain boundaries, but after thermal annealing, grains grow and form nanocrystalline structure with a grain size of 8 nm. The thin sheets consisted of the face-centered cubic phases of crystal unit cells, separated by grain boundaries. For the penetration simulations, four velocities were chosen 102, 103, 104 and 105 m/s. The first two velocities are called high velocity case and the rest two velocities are the hypervelocity case. Our results show that, as the penetration rate increases, more stresses are required to move the projectile through the Al film due to temperature effects from the high velocity to hypervelocity case. In addition, defects, such as dislocations, increase during the projectile penetration. In the high velocity case, the penetrated hole in the film may be recovered, but not in the hypervelocity case. The temperature difference increased in the hypervelocity case is significantly than that in the high velocity case.

Statistics of reversible transitions in two-state trajectories in force-ramp spectroscopy

A possible way to extract information about the reversible dissociation of a molecular adhesion bond from force fluctuations observed in force ramp experiments is discussed. For small loading rates the system undergoes a limited number of unbinding and rebinding transitions observable in the so-called force versus extension (FE) curves. The statistics of these transient fluctuations can be utilized to estimate the parameters for the rebinding rate. This is relevant in the experimentally important situation where the direct observation of the reversed FE-curves is hampered, e.g., due to the presence of soft linkers. I generalize the stochastic theory of the kinetics in two-state models to the case of time-dependent kinetic rates and compute the relevant distributions of characteristic forces. While for irreversible systems there is an intrinsic relation between the rupture force distribution and the population of the free-energy well of the bound state, the situation is slightly more complex if reversible systems are considered. For a two-state model, a "stationary" rupture force distribution that is proportional to the population can be defined and allows to consistently discuss quantities averaged over the transient fluctuations. While irreversible systems are best analyzed in the soft spring limit of small pulling device stiffness and large loading rates, here I argue to use the stiffness of the pulling device as a control parameter in addition to the loading rate.

Realizing nano-confinement of magnesium for hydrogen storage using vapour transport deposition

A new approach was developed to successfully load Mg into the nanometre-sized pores of an anodic aluminium oxide (AAO) template for realizing the nano-confinement of Mg. Structural characterization shows that Mg nano-particles are nucleated along the AAO pipe wall together with the formation of MgO and Mg17Al12 as by-products. The flow rate of argon gas, the temperature of the AAO template and the transporting distance between the Mg vapour source and the AAO template were optimized to achieve the confinement of Mg nano-particles with larger loading rate. Under optimized deposition conditions, the particle size of the loaded Mg is less than 100 nm and the effective filling factor is about 35 wt%. The confined Mg/MgH2 even after 10 de-/hydrogenation cycles still shows favourable kinetics. Furthermore, the slight reduction in hydrogen desorption enthalpy and entropy of MgH2 from (74.42 ± 0.12) to (73.21 ± 0.04) kJ·mol−1 and (130.98 ± 0.05) to (130.11 ± 0.24) J·mol−1·K−1 is also found in the present nano-confinement.

Simulations reveal that the HIV-1 gp120-CD4 complex dissociates via complex pathways and is a potential target of the polyamidoamine (PAMAM) dendrimer

The polyamidoamine (PAMAM) dendrimer prevents HIV-1 entry into target cells in vitro. Its mechanism of action, however, remains unclear and precludes the design of potent dendrimers targeting HIV-1 entry. We employed steered molecular dynamics simulations to examine whether the HIV-1 gp120-CD4 complex is a target of PAMAM. Our simulations mimicked single molecule force spectroscopy studies of the unbinding of the gp120-CD4 complex under the influence of a controlled external force. We found that the complex dissociates via complex pathways and defies the standard classification of adhesion molecules as catch and slip bonds. When the force loading rate was large, the complex behaved as a slip bond, weakening gradually. When the loading rate was small, the complex initially strengthened, akin to a catch bond, but eventually dissociated over shorter separations than with large loading rates. PAMAM docked to gp120 and destabilized the gp120-CD4 complex. The rupture force of the complex was lowered by PAMAM. PAMAM disrupted salt bridges and hydrogen bonds across the gp120-CD4 interface and altered the hydration pattern of the hydrophobic cavity in the interface. In addition, intriguingly, PAMAM suppressed the distinction in the dissociation pathways of the complex between the small and large loading rate regimes. Taken together, our simulations reveal that PAMAM targets the gp120-CD4 complex at two levels: it weakens the complex and also alters its dissociation pathway, potentially inhibiting HIV-1 entry.