High Mechanical Strain Research Articles

Numerical and experimental investigation of the mesoscale fracture behaviour of quenched steels

AbstractDuring heat treatment processes, especially during quenching, cracks may form because of the presence of high thermal and mechanical stresses and strains. Notwithstanding the fact that increasingly detailed modelling for heat treatment is being performed (considering, i.a., grain size, creep and transformation plasticity), homogeneous microstructures are still normally assumed. Chemical and hence structural inhomogeneities are not commonly explicitly considered, which is especially accentuated in the case of real parts simulation because of the resulting numerical problem's size. Intensive quenching on a cylindrical specimen of 100Cr6 (SAE) steel is proposed here to experimentally investigate the microcrack generation. A finite element based model is proposed to numerically evaluate the fracture behaviour in a two‐step simulation. First, by solving the quenching problem in direct correspondance with the experimental test performed, and second, by studying the mesoscale response taking into account the influence of second phase particles in a representative volume element based approach. The maximum principal stress criterion is used to trigger the fracture by means of the extended finite element method at the mesoscale. The trend to form cracks in the surface region, experimentally observed, has been well captured by the model. The influence of carbides sizes and content on the mesoscale fracture response has been numerically analysed as well. A good agreement has been reached between the simulations and the experimental results, exhibiting the potential of the introduced approach to be used as a failure prediction methodology.

Oxidative damage to human parametrial ligament fibroblasts induced by mechanical stress.

The aim of the present study was to explore the underlying mechanisms of the roles of mechanical factors in the pathogenesis of pelvic organ prolapse (POP). The experiments were performed on fibroblasts derived from uterosacral ligaments and cardinal ligaments of patients who received total hysterectomy due to benign disease excluding POP. Fibroblasts were cultured after collagenase digestion and identified by morphological observation and immunocytochemical methods. A four‑point bending device was used to subject fibroblasts at passage 4‑6 to strains of 0, 1,333 µ (1 mm), 2,666 µ (2 mm) or 5,333 µ (4 mm) at a frequency of 0.1 Hz for 4 h. Intracellular reactive oxygen species (ROS) were quantified using the fluorescent probe 2',7'‑dichlorodihydrofluorescein diacetate. Changes in the mitochondrial membrane potential were verified using the fluorescent dye JC‑1, and apoptosis was detected using Annexin V/propidium iodide staining and flow cytometric analysis. Mechanical strain changed the morphology and adherence ability of parametrial ligament fibroblasts. Furthermore, the production of ROS was significantly increased and the mitochondrial membrane potential obviously declined with the enhancement of mechanical stress loading. In addition, the apoptotic rate of fibroblasts subjected to high mechanical strain was significantly increased compared with that in fibroblast under low‑intensity strain. In conclusion, the present study showed that mechanical strain enhanced intracellular ROS levels, decreased the mitochondrial membrane potential and increased the apoptotic rate in human parametrial ligament fibroblasts, which may contribute to POP.

Reinforcing silica aerogels with tungsten disulfide nanotubes

Silica aerogels are unique solids with extremely high porosity (>99.5% air by volume), transparency and low density. With their high surface area and thermal resistivity they make excellent heat insulators. However, due to their fine structure they are fragile and therefore impractical for structural applications. To improve their mechanical properties we suggest incorporation of minute amounts of tungsten disulfide nanotubes. Nanotubes of tungsten disulfide are known for their high mechanical strength, strain and thermal stability. Adding some 0.1–1 wt% of tungsten disulfide nanotubes to a variety of polymers clearly lead to substantial improvement in their mechanical properties.The current study reports the preparation of silica aerogels compounded with small amounts of tungsten disulfide nanotubes. Three-point bending and uniaxial compression tests of the composite aerogel revealed 85% and 23% improvement in the composite material toughness, respectively.

Low-frequency high-magnitude mechanical strain of articular chondrocytes activates p38 MAPK and induces phenotypic changes associated with osteoarthritis and pain.

Osteoarthritis (OA) is a debilitating joint disorder resulting from an incompletely understood combination of mechanical, biological, and biochemical processes. OA is often accompanied by inflammation and pain, whereby cytokines associated with chronic OA can up-regulate expression of neurotrophic factors such as nerve growth factor (NGF). Several studies suggest a role for cytokines and NGF in OA pain, however the effects of changing mechanical properties in OA tissue on chondrocyte metabolism remain unclear. Here, we used high-extension silicone rubber membranes to examine if high mechanical strain (HMS) of primary articular chondrocytes increases inflammatory gene expression and promotes neurotrophic factor release. HMS cultured chondrocytes displayed up-regulated NGF, TNFα and ADAMTS4 gene expression while decreasing TLR2 expression, as compared to static controls. HMS culture increased p38 MAPK activity compared to static controls. Conditioned medium from HMS dynamic cultures, but not static cultures, induced significant neurite sprouting in PC12 cells. The increased neurite sprouting was accompanied by consistent increases in PC12 cell death. Low-frequency high-magnitude mechanical strain of primary articular chondrocytes in vitro drives factor secretion associated with degenerative joint disease and joint pain. This study provides evidence for a direct link between cellular strain, secretory factors, neo-innervation, and pain in OA pathology.

The SUN protein UNC-84 is required only in force-bearing cells to maintain nuclear envelope architecture.

The nuclear envelope (NE) consists of two evenly spaced bilayers, the inner and outer nuclear membranes. The Sad1p and UNC-84 (SUN) proteins and Klarsicht, ANC-1, and Syne homology (KASH) proteins that interact to form LINC (linker of nucleoskeleton and cytoskeleton) complexes connecting the nucleoskeleton to the cytoskeleton have been implicated in maintaining NE spacing. Surprisingly, the NE morphology of most Caenorhabditis elegans nuclei was normal in the absence of functional SUN proteins. Distortions of the perinuclear space observed in unc-84 mutant muscle nuclei resembled those previously observed in HeLa cells, suggesting that SUN proteins are required to maintain NE architecture in cells under high mechanical strain. The UNC-84 protein with large deletions in its luminal domain was able to form functional NE bridges but had no observable effect on NE architecture. Therefore, SUN-KASH bridges are only required to maintain NE spacing in cells subjected to increased mechanical forces. Furthermore, SUN proteins do not dictate the width of the NE.

Topographical Analysis of Non-Glaucomatous Myopic Optic Discs Using a Confocal Scanning Laser Ophthalmoscope (TopSS)

Objectives: To show normative data of optic discs and the mechanism of glaucoma in people with myopia. Design: Cross-sectional study. Participants: This study investigated 89 Korean adults with myopia but without glaucoma. Methods: Patients were divided into three groups according to the refractive error: low, moderate, and high; and axial length: normal or below normal length, moderately long, and extremely long. Optic disc variables were obtained by confocal scanning laser ophthalmoscope and compared among groups. Results: The optic disc parameters have a correlation between the refractive error and the optic disc parameters such as average depth, volume below, and half-depth volume. Those parameters also decreased as the axial length increased. The thickness of the volume above decreased significantly as the axial length increased, but a similar relationship was not evident with the refractive error change. In addition, the optic disc parameters were analyzed with respect to the 12 clockwise directions. Conclusions: Analyses of optic disc parameters provided by TopSS™ revealed the height of the disc decreased as the myopic refractive error and/or axial length increased. The RNFL bundle became compacted in the thinner disc of the myopic population. This could be an explanation for the fragility of the RNFL in the myopic population. The 12 radial section analyses revealed the shallow cupping at the temporal side in the high-myopic, very-long-axis group. The neuroretinal rim (NRR) height significantly decreased at the superior and inferior sides. These findings suggest that the RNFL bundle should be under high mechanical strain in these sectors.

High Mechanical Strain of Intervertebral Disc Cells Promotes Secretion of Inflammatory Factors Associated with Disc Degeneration and Pain

IntroductionLow back pain is a debilitating disorder affecting a multitude of people and is currently ranked sixth among costliest treatable chronic illnesses.1 Low back pain is often attributed to...

In Operando Neutron Reflectometry Measurements Demonstrate Structural Stability in Thin Film Silicon Anodes for Lithium Ion Batteries

Despite its incredibly high theoretical capacity (~4200 mA-h/g), implementation of Si electrodes as high-capacity Li-battery anodes is hindered by poor mechanical durability. Si lithiation is accompanied by very high mechanical strain values, with nearly 370% volume expansion at maximum capacity, which typically leads to fracture and pulverization of the material and eventual battery failure. While numerous strategies have been employed to improve the durability of Si anodes, including nano-structured anode architectures, composite anode materials, and protective coatings, efforts have yet to identify a Si anode design that is mechanically robust and maintains a stable anode capacity. At least part of the difficulty is due to a lack of fundamental insight into the correlation between structure, mechanical properties, and function for Si anodes, owing to a paucity of in situ techniques to definitively observe them. In this presentation, we report the structural and composition changes in an amorphous thin-film silicon anode with a protective Al sub-oxide (AlOx) capping layer, using in operando neutron reflectivity (NR) and electronic impedance spectroscopy (EIS) measurements. NR measurements were carried out in situ on an operating Li half-cell at various charge states over six shallow charge-discharge cycles. These measurements quantify the correlation between mesoscopic strain and the degree of lithiation in a 10-nm thick amorphous silicon thin-film anode, which expands and contracts with repeated cycling (Figure 1). Results demonstrate the mechanical durability of both the Si thin-film anode and the protective AlOx layer, which maintain their low surface roughness and film integrity over the course of the measurements. While the macroscopic strain of the Si shows significant non-linearity with Li content after several shallow charge-discharge cycles, in agreement with previous reports1, careful inclusion of a-Si microstructural effects (via direct measurement of the a-Si porosity) reveal that the volumetric strain for the solid portion of a-Si thin films varies linearly with lithium content (Figure 2). Results demonstrate that the porosity is eliminated during the expansion that accompanies lithiation, and is then recovered during subsequent de-lithiation. Furthermore, it is shown here that the delithiated a-Si porosity does not vary significantly over the course of the measurements – ranging from 10.0 [5.4 – 28.0]% in the as-deposited state to 13.1 [10.02 – 15.73]% after 6 shallow charge and discharge cycles – demonstrating the structural reproducibility of the thin-film anode.

High mechanical strain of primary intervertebral disc cells promotes secretion of inflammatory factors associated with disc degeneration and pain

IntroductionExcessive mechanical loading of intervertebral discs (IVDs) is thought to alter matrix properties and influence disc cell metabolism, contributing to degenerative disc disease and development of discogenic pain. However, little is known about how mechanical strain induces these changes. This study investigated the cellular and molecular changes as well as which inflammatory receptors and cytokines were upregulated in human intervertebral disc cells exposed to high mechanical strain (HMS) at low frequency. The impact of these metabolic changes on neuronal differentiation was also explored to determine a role in the development of disc degeneration and discogenic pain.MethodsIsolated human annulus fibrosus (AF) and nucleus pulposus (NP) cells were exposed to HMS (20% cyclical stretch at 0.001 Hz) on high-extension silicone rubber dishes coupled to a mechanical stretching apparatus and compared to static control cultures. Gene expression of Toll-like receptors (TLRs), neuronal growth factor (NGF) and tumour necrosis factor α (TNFα) was assessed. Collected conditioned media were analysed for cytokine content and applied to rat pheocromocytoma PC12 cells for neuronal differentiation assessment.ResultsHMS caused upregulation of TLR2, TLR4, NGF and TNFα gene expression in IVD cells. Medium from HMS cultures contained elevated levels of growth-related oncogene, interleukin 6 (IL-6), IL-8, IL-15, monocyte chemoattractant protein 1 (MCP-1), MCP-3, monokine induced by γ interferon, transforming growth factor β1, TNFα and NGF. Exposure of PC12 cells to HMS-conditioned media resulted in both increased neurite sprouting and cell death.ConclusionsHMS culture of IVD cells in vitro drives cytokine and inflammatory responses associated with degenerative disc disease and low-back pain. This study provides evidence for a direct link between cellular strain, secretory factors, neoinnervation and potential degeneration and discogenic pain in vivo.

Mechanical strain induces the production of spheroid mineralized microparticles in the aortic valve through a RhoA/ROCK-dependent mechanism

Calcific aortic valve disease (CAVD) is a chronic disorder characterized by an abnormal mineralization of the leaflets, which is accelerated in bicuspid aortic valve (BAV). It is suspected that mechanical strain may promote/enhance mineralization of the aortic valve. However, the effect of mechanical strain and the involved pathways during mineralization of the aortic valve remains largely unknown. Valve interstitial cells (VICs) were isolated and studied under strain conditions. Human bicuspid aortic valves were examined as a model relevant to increase mechanical strain. Cyclic strain increased mineralization of VICs by several-fold. Scanning electron microscope (SEM) and energy dispersive X-ray (EDX) analyses revealed that mechanical strain promoted the formation of mineralized spheroid microparticles, which coalesced into larger structure at the surface of apoptotic VICs. Apoptosis and mineralization were closely associated with expression of ENPP1. Inhibition of ENPP1 greatly reduced mineralization of VIC cultures. Through several lines of evidence we showed that mechanical strain promoted the export of ENPP1-containing vesicles to the plasma membrane through a RhoA/ROCK pathway. Studies conducted in human BAV revealed the presence of spheroid mineralized structures along with the expression of ENPP1 in areas of high mechanical strain. Mechanical strain promotes the production and accumulation of spheroid mineralized microparticles by VICs, which may represent one important underlying mechanism involved in aortic valve mineralization. RhoA/ROCK-mediated export of ENPP1 to the plasma membrane promotes strain-induced mineralization of VICs.

Local Mechanical Stimuli Regulate Bone Formation and Resorption in Mice at the Tissue Level

Bone is able to react to changing mechanical demands by adapting its internal microstructure through bone forming and resorbing cells. This process is called bone modeling and remodeling. It is evident that changes in mechanical demands at the organ level must be interpreted at the tissue level where bone (re)modeling takes place. Although assumed for a long time, the relationship between the locations of bone formation and resorption and the local mechanical environment is still under debate. The lack of suitable imaging modalities for measuring bone formation and resorption in vivo has made it difficult to assess the mechanoregulation of bone three-dimensionally by experiment. Using in vivo micro-computed tomography and high resolution finite element analysis in living mice, we show that bone formation most likely occurs at sites of high local mechanical strain (p<0.0001) and resorption at sites of low local mechanical strain (p<0.0001). Furthermore, the probability of bone resorption decreases exponentially with increasing mechanical stimulus (R2 = 0.99) whereas the probability of bone formation follows an exponential growth function to a maximum value (R2 = 0.99). Moreover, resorption is more strictly controlled than formation in loaded animals, and ovariectomy increases the amount of non-targeted resorption. Our experimental assessment of mechanoregulation at the tissue level does not show any evidence of a lazy zone and suggests that around 80% of all (re)modeling can be linked to the mechanical micro-environment. These findings disclose how mechanical stimuli at the tissue level contribute to the regulation of bone adaptation at the organ level.

Elastic behaviour of zirconium titanate bulk material at room and high temperature

Abstract Zirconium titanate (ZrTiO4) is a well known compound in the field of electroceramics, however, its potential for structural applications has never been analysed. Moreover, it is compatible with zirconia, thus, zirconium titanate–zirconia composites might have potential for structural applications in oxidizing atmospheres. Nevertheless, there are currently no data about elastic properties of zirconium titanate materials in the literature. In view of the importance of these properties for the structural integrity of components subjected to high temperature and mechanical strains, an attempt was done in this work to determine the elastic properties of ZrTiO4, both at room and high temperature. Young's modulus (161 ± 4 GPa), shear modulus (61 ± 1 GPa) and Poisson's ratio (0.32 ± 0.01) values at room temperature have been estimated for a fully dense single phase ZrTiO4 material from experimental data of sintered single phase ZrTiO4 materials with different porosities (6–19%). Values for room temperature Young's modulus are in agreement with those obtained by nanoindentation. Young's modulus up to 1400 °C shows an unusual dependence on temperature with no significant variation up to 500 °C an extremely low decrease from 500 to 1000 °C (≈0.02–0.03% every 100 °C) followed by a larger decrease that can be attributed to grain boundary sliding up to 1400 °C.

Noninvasive high resolution mechanical strain maps of the spine intervertebral disc using nonrigid registration of magnetic resonance images

High resolution strain measurements are of particular interest in load bearing tissues such as the intervertebral disc (IVD), permitting characterization of biomechanical conditions which could lead to injury and degenerative outcomes. Magnetic resonance (MR) imaging produces excellent image contrast in cartilaginous tissues, allowing for image-based strain determination. Nonrigid registration (NRR) of MR images has previously demonstrated sub-voxel registration accuracy although its accuracy and precision in determining strain has not been evaluated. Accuracy and precision of NRR-derived strain measurements were evaluated using computer generated deformations applied to both computer generated images and MR images. Two different measures of registration similarity—the cost function which drives the registration algorithm—were compared: Mutual Information (MI) and Least Squares (LS). Strain error was evaluated with respect to signal-to-noise ratio (SNR), contrast-to-noise ratio (CNR), and strain heterogeneity. Additionally, the creep strain response from an in vitro loaded porcine IVD is shown and comparisons between similarity measures are presented. MI showed a decrease in strain precision with increasing CNR and decreasing SNR while LS was insensitive to both. Both similarity measures showed a decrease in strain precision with increasing strain heterogeneity. When computer generated heterogeneous strains were applied to MR images of the IVD, LS showed substantially lower strain error in comparison to MI. Results suggest that LS-driven NRR provides a more accurate image-based method for mapping large and heterogeneous strain fields and this method can be applied to studies of the IVD and, potentially, other soft tissues which present sufficient image texture.

Performance of Piezoelectric Power Generation of Multilayered Poly(vinylidene fluoride) under High Mechanical Strain

In this study, we examine the effective usage of a piezoelectric polymer for electric power generation on the basis of polymeric features such as high robustness, high flexibility, and easy formability. Theoretical calculation elucidates the potential of piezoelectric generation of the polymer with a large elastic strain. It is confirmed by the experimental results that the multilayered structure of the rolled poly(vinylidene fluoride) (PVDF) films enhances the performance of piezoelectric generation in proportion to the number of the PVDF layers and shows an apparent d33 of 7.1 nC/N for the film rolled 200 times. The generated charge as a function of the applied stress shows a linear increase. As a practical usage, we design the mechanical system equipped with a lever for applying a large foot-step-derived stress to embedded PVDF films. The performance of electric power generation using the system and the charging characteristics with the relatively large load capacitor are presented.

Performance of Piezoelectric Power Generation of Multilayered Poly(vinylidene fluoride) under High Mechanical Strain

Performance of Piezoelectric Power Generation of Multilayered Poly(vinylidene fluoride) under High Mechanical Strain

Fiber Myosin Heavy Chain Polymorphism is Associated with a Heightened Susceptibility to Eccentric Damage

The purpose of this study was to model the relationship between fiber myosin heavy chain (MHC) isoform content and susceptibility to damage by a standardized eccentric contraction (+25% change in fiber length; 50% of unloaded shortening velocity, Vo). Damage was quantified as the pre- to post-eccentric change in Ca2+-activated force. Chemically skinned fibers from the soleus and EDL of C57BL/6 mice were studied in order to obtain MHC monomorphic (type I, IIa, IIx, IIb) and polymorphic (I/IIa, IIa/IIx, IIx/IIb) fibers. Fiber MHC isoform content was determined by SDS-PAGE. The mean (±SE) pre- to post-eccentric change in force was −5.2 ± 0.5 kN/m2 (n = 24) for type I fibers, −18.3 ± 1.5 (7) for I/IIa, −5.3 ± 0.7 (27) for IIa, −18.1 ± 2.3 (5) for IIa/IIx, −5.4 ± 0.6 (34) for IIx, −17.8 ± 1.1 (11) for IIx/IIb, and −5.7 ± 0.8 (24) for IIb. Multiple linear regression indicated that, independent of MHC content, greater pre-specific force was associated with a slightly greater post-force deficit (slope = 0.94). With pre-eccentric force held constant, no relationship was found between fiber Vo and post-eccentric force (p = 0.716) . In contrast, data were well described by a model using pre-eccentric force and MHC polymorphism as predictors (p < 0.001; r2 = 0.97): post-force of monomorphic fibers = 0.94(pre-force) + 2.04 kN/m2 post-force of polymorphic fibers = 0.94(pre-force) - 12.15 kN/m2 The significant difference (p < 0.001) in model y-intercepts reveals that, at similar pre-eccentric specific force, MHC polymorphism was associated with a 14 kN/m2 greater eccentric-induced reduction in force vs. monomorphic fibers. We conclude that MHC polymorphism is associated with a heightened sensitivity to high mechanical strain at the level of the myofilament lattice or cytoskeleton.

Which Types of Activities Are Associated With Risk of Recurrent Falling in Older Persons?

This study explored the associations between various types of activities, their underlying physical components, and recurrent falling in community-dwelling older persons. This study included 1,329 community-dwelling persons (>or=65 years) of the Longitudinal Aging Study Amsterdam (LASA). The time spent in walking, cycling, light and heavy household activities, and two sports was measured using the LASA Physical Activity Questionnaire (LAPAQ). Physical activity components included strength, intensity, mechanical strain, and turning. Time to second fall in a 6-month period was measured during 3 years with fall calendars. Cox proportional hazards models were adjusted for confounders and stratified for physical performance and sex in case of significant (p < .10) interaction. During 3 years, 325 (24.5%) persons became recurrent fallers. In women, doing light (hazard ratios [HRs] = 0.40, 95% confidence intervals [CIs] = 0.20-0.79) or heavy household activities (HR = 0.63, CI = 0.44-0.79) was associated with a decreased risk of recurrent falling. In persons with good physical performance, doing sports (HR = 1.56, CI = 1.07-2.28), high intensity (HR > 1.75, CI = 1.09-3.16), and high mechanical strain (HR = 1.70, CI = 1.01-2.83) activities was associated with an increased risk of recurrent falling. The results suggest that the relationship between physical activity and recurrent falling differs per type of activity and is modified by physical performance. Doing household activities was associated with a decreased risk of recurrent falling in women. In physically fit older persons, doing sports or activities with high intensity or mechanical strain demands was associated with an increased risk of recurrent falling.

Physical activity and incident clinical knee osteoarthritis in older adults

To study the relationship between 4 components of physical activity and the 12-year incidence of clinical knee osteoarthritis (OA) among older adults. Longitudinal data from 1,678 men and women, ages 55-85 years, were collected in the Longitudinal Aging Study Amsterdam. Incident clinical knee OA was defined by an algorithm using self-report and general practitioner data. Physical activity was assessed by a validated questionnaire from which 4 physical activity component scores were created: muscle strength, intensity, mechanical strain, and turning actions. Cox proportional hazards models were conducted to examine the relationship between these scores and incident knee OA and reported as hazard ratios (HRs) with 95% confidence intervals (95% CIs). During 12 years of followup, 463 respondents (28%) developed clinical knee OA. A high mechanical strain score (HR 1.43, 95% CI 1.15-1.77) and a low muscle strength score (HR 1.30, 95% CI 1.01-1.68) were associated with an increased risk of knee OA after adjustment for age, sex, region of living, education, lifetime physical work demands, lifetime general physical activity, body mass index, current total physical activity level, and depression. No association was observed in the intensity and turning actions components. The results were similar for men and women, and for obese and nonobese respondents. Older adults who perform low muscle strength activities or activities causing high mechanical strain had an increased risk of clinical knee OA. These results suggest that specific components of physical activity may influence the development of knee OA.

Were neandertal and modern human cranial differences produced by natural selection or genetic drift?

Most evolutionary explanations for cranial differences between Neandertals and modern humans emphasize adaptation by natural selection. Features of the crania of Neandertals could be adaptations to the glacial climate of Pleistocene Europe or to the high mechanical strains produced by habitually using the front teeth as tools, while those of modern humans could be adaptations for articulate speech production. A few researchers have proposed non-adaptive explanations. These stress that isolation between Neandertal and modern human populations would have lead to cranial diversification by genetic drift (chance changes in the frequencies of alleles at genetic loci contributing to variation in cranial morphology). Here we use a variety of statistical tests founded on explicit predictions from quantitative- and population-genetic theory to show that genetic drift can explain cranial differences between Neandertals and modern humans. These tests are based on thirty-seven standard cranial measurements from a sample of 2524 modern humans from 30 populations and 20 Neandertal fossils. As a further test, we compare our results for modern human cranial measurements with those for a genetic dataset consisting of 377 microsatellites typed for a sample of 1056 modern humans from 52 populations. We conclude that rather than requiring special adaptive accounts, Neandertal and modern human crania may simply represent two outcomes from a vast space of random evolutionary possibilities.

Single Event–Driven Export of Polycyclic Aromatic Hydrocarbons and Suspended Matter from Coal Tar–Contaminated Soil

Mobile colloidal and suspended matter is likely to affect the mobility of polycyclic aromatic hydrocarbons (PAHs) in the unsaturated soil zone at contaminated sites. We studied the release of mobile particles and dissolved organic matter as a function of variable climatic boundary conditions, and their effect on the export of PAHs at a coal tar–contaminated site using zero‐tension lysimeters. Seepage water samples were analyzed for dissolved organic carbon (DOC), pH, electrical conductivity, turbidity, and particles larger than 0.7 μm. The 16 Environmental Protection Agency PAHs were analyzed in the filtrate &lt;0.7 μm and in the particle fraction. Our results show that extended no‐flow periods that are followed by high‐intensity rain events, such as thunderstorms, promote the mobilization of particles in the size 0.7 to 200 μm. Mobilization is enforced by extended drying during summer. High particle concentrations are also associated with freezing and thawing cycles followed by either rain or snowmelt events. The export of PAHs is strongly connected to the release of particles in the 0.7‐ to 200‐μm size fraction. During the 2‐yr monitoring period, up to 0.418 μg kg−1 PAHs were mobilized in the filtrate (&lt;0.7 μm) while the eightfold mass, 3.36 μg kg−1, was exported with the retentate (0.7–200 μm). Equilibrium dissolution of PAHs and transport in the dissolved phase seem to be of minor importance for the materials studied. Extreme singular‐release events occurred in January 2003 and January 2004, when up to 55 μg L−1 PAHs per one single seepage event were observed within the retentate. Freezing and thawing cycles affect the PAH source materials, that is, the remnants of the nonaqueous phase liquid (NAPL). High mechanical strain during freezing results in the formation of particles. At the onset of the thawing and following rain or snowmelt events, PAHs associated with these particles are then exported from the lysimeter.