Cold Hardening Research Articles

Fatigue Fracture Mechanism and Life Prediction of TA1 Titanium Alloy Clinched Joints

ABSTRACTThis study investigated the fatigue fracture mechanisms and life prediction of clinched joints made from titanium alloy TA1. The fatigue tests revealed that TA1 titanium alloy clinched joints exhibited failure characterized by fracture of the lower plate at three distinct fatigue load levels. Additionally, finite element analysis indicated that cold work hardening enhanced the fatigue performance of these joints. Observations of fracture surfaces using scanning electron microscopy identified the crack source and its propagation path, which correlated with the location of maximum principal stress from the finite element simulations. Fretting wear was also observed in this critical region. Furthermore, fatigue life predictions for TA1 titanium alloy clinched joints were made using Paris' law and the local strain approach. Both methods closely matched experimental results across different fatigue life intervals. Overall, the local strain approach exhibited superior predictive capability compared to Paris' law, taking into account various influencing factors.

Integrated transcriptional and biochemical profiling suggests mechanisms associated with rapid cold hardening in adult Liriomyza trifolii (Burgess)

The leafminer Liriomyza trifolii causes severe economic damage on ornamental and horticultural crops in China. Rapid cold hardening (RCH) is a phenomenon where cold tolerance in insects can be significantly enhanced after a short-term acclimation to low temperatures. In this study, the regulation of transcription in response to cold hardening was investigated in L. trifolii adults, and fatty acids and cryoprotectant levels were measured. The composition of fatty acids changed after RCH treatment, and glucose and trehalose levels showed significant accumulation after acclimation, thus indicating that changes in fatty acids and cryoprotectants contribute to RCH in L. trifolii. RNA-seq was used to analyze transcriptional regulation after a 4 h hardening period and showed that differentially expressed genes clustered in multiple metabolic pathways, which indicates the importance of transcriptional regulation in RCH. This study expands our knowledge of biochemical and transcriptional changes in L. trifolii during cold hardening and provides a basis for further investigations aimed at understanding thermal adaptation in insects.

A comparative study of self pierceing riveting and mechanical clinch of DP590-Al5754 high-strength steel and aluminum alloys

This paper presents a comparative study of two joining processes, self piercing riveting (SPR) and mechanical clinch, used to join DP590 high-strength steel and Al5754 aluminum alloy. A comparative study of microhardness, tensile shear properties, fatigue properties, and economics of joints from both processes was conducted. The findings indicate that the highest hardness levels are observed in the rivet leg region for SPR joints and in the neck region for mechanical clinch joints. The maximum failure load and energy absorption values of SPR joints were found to be 1.46 and 9.07 times higher, respectively, than those of mechanical clinch joints. The static tensile test results demonstrate that the strength and hardness of SPR joints in aluminum sheets subjected to cold work hardening are significantly lower than those of steel sheets. Therefore, the failure of SPR joints is primarily attributed to the deformation and fracture of the lower aluminum sheet. Mechanical clinch joints fail by neck fracture because the steel sheet neck becomes brittle by cold work hardening and the neck thickness is small. The fatigue behavior of SPR joints was observed to be superior to that of mechanical clinch joints. The findings of the scanning electron microscopy and energy spectrum analysis suggest that fretting wear between the upper and lower sheets results in fatigue fracture of the lower sheet in the joints. When joining the same material on a large scale, the selection of mechanical clinch over SPR can prove an effective method of reducing costs. Furthermore, the selection of a set of dies with an extended life can contribute to the reduction of joining costs.

Cold tolerance strategy, supercooling, and cold hardening in three populations of the jumping spider Phidippus audax (Araneae: Salticidae)

Cold tolerance strategy, supercooling, and cold hardening in three populations of the jumping spider Phidippus audax (Araneae: Salticidae)

Possibilities for reproduction and archiving resulting in a clone collection of a unique grey poplar (Populus × canescens Aiton Sm.) population in the Czech Republic

Abstract Floodplain forests as one of the most endangered ecosystems in Europe have recently been impacted by fungal pathogens Phytophtora sp. and Hymenoscyphus fraxineus (chalara). Grey poplar (Populus × canescens Aiton Sm.) can be used as one of well adapted tree species for the reforestation of withering stands of ash (Fraxinus sp.). A unique population of grey poplar (Populus × canescens Aiton Sm.) characterized by desirable phenotypic traits was used for this purpose. The gender distribution was asymmetric; out of 155 individuals, 113 were female. Out of 33 different genotypes determined in the population, 15 were used as a source of approved forest reproductive material. Vegetative reproduction methods (ex situ clonal reproduction by micropropagation and cuttings) were developed and used, to rapidly initiate the recovery of forest stands of grey poplar. In total, 940 explants were successfully micropropagated and adapted to natural conditions, to ensure a genetically diverse source of viable plants used for reforestation. Moreover, we used methodological procedures of micropropagation for setting up cryopreservation technique. With respect to long-term storage of valuable grey poplar genotypes, modulation of gene expression by cold hardening during cryopreservation revealed significant changes in a few candidate genes involved in plant cellular processes.

Transgenerational cross‐susceptibility to heat stress following cold and desiccation acclimation in the Angoumois grain moth

AbstractThe Angoumois grain moth, Sitotroga cerealella (Olivier), is a significant cosmopolitan primary pest of cereals worldwide and has thrived in divergent environments. However, the mechanisms underlying its survival in multiple contrasting environments are poorly understood. Here, we hypothesised that when facing diverse environmental stress, F1 generation exhibits transgenerational cross‐protection as a mechanism to persist under divergent stressful environments. Notably, F1 acclimation to cold or desiccation conditions could either enhance or lower heat tolerance in the F2 generation. Specifically, we tested whether typical diurnal fluctuations and/or winter rapid or chronic cold temperatures (18–22°C) as well as desiccation acclimation of F1 parental population yields transgenerational cross‐protection/susceptibility to heat stress on F2 offspring. F1 moths were exposed to cold hardening (2 h), chronic (72 h) and variable (fluctuating between 18 and 22°C for 72 h) temperature treatment groups. Desiccation treatment included incubation at 0%–1% relative humidity (24 h). F2 generation moths were then assessed for heat tolerance using critical thermal maxima (CTmax) at three different ramping rates (0.06, 0.25 and 0.5°C/min) as well as heat knockdown time (HKDT). Findings indicated that (i) desiccation, cold hardening and chronic low‐temperature acclimations in F1 reduced heat tolerance in F2 populations and (ii) ramping rate was crucial to decipher differences between treatment groups, with lower ramping rates associated with lower CTmax. Transgenerational cross‐susceptibility to heat stress indicates possible fitness costs of exposure to multiple contrasting stressors in the Angoumois grain moth and can be used in designing physical pest management strategies.

Autumn cold acclimation and freezing tolerance of three oak species in semi-Mediterranean Zagros forests

Aim of study: To identify and compare the early frost resistance mechanisms in three oak species (Quercus brantii, Quercus libani and Quercus infectoria). Area of study: Zagros forests of Iran. Material and methods: The physiological and biochemical variables such as chlorophyll fluorescence, relative water content (RWC), electrolyte leakage, and osmotic metabolite content, such as proline, glucose, and potassium of three oak species seedlings with varying altitudinal and latitudinal ranges were measured under various treatments, including cold treatments (4°C: control, -20°C (1 hour) and -20°C (2 hours)) and four levels of hardening steps with decreasing temperature and photoperiod. Main results: Results showed that decreasing photoperiod and temperature during cold hardening was associated with decreasing Fv/Fm, ΦPSII and electron transport rate, increasing (NPQ) measured from chlorophyll fluorescence, as well as increasing osmotic metabolite content and decline of RWC, except the glucose content decreased in Q. brantii from lower altitudes and south aspect. On the other hand, Q. libanii, which originates from higher altitudes and north aspect showed the strongest cold-resistance and faster developing cold-acclimation capacity using earlier accumulation of osmotic metabolites, diminishing RWC and subsequently lowest EL compared to the other oak species. Research highlights: The physiological and biochemical responses of oak species differed based on origin and there was a positive relation between osmotic metabolite content, NPQ, altitude, and cold stress resistance. These physiological responses, especially NPQ (as a fast and non-invasive tool) provide a quantitative assessment of the risks associated with autumn freezing in different oak species and ecotypes relevant to conservation and reforestation projects of the Zagros forests under changing climatic conditions.

Au-Based Nanoparticles Enhance Low Temperature Tolerance in Wheat by Regulating Some Physiological Parameters and Gene Expression.

One of the key problems of biology is how plants adapt to unfavorable conditions, such as low temperatures. A special focus is placed on finding ways to increase tolerance in important agricultural crops like wheat. Au-based nanoparticles (Au-NPs) have been employed extensively in this area in recent years. Au-NPs can be produced fast and easily using low-cost chemical reagents. When employed in microdoses, Au-NPs are often non-toxic to plants, animals, and people. In addition, Au-NPs mainly have favorable impacts on plants. In this study, we investigated the effect of Au-NP seed nanopriming (diameter 15.3 nm, Au concentration 5-50 µg mL-1) on cold tolerance, as well as some physiological, biochemical and molecular parameters, of cold-sustainable wheat (Triticum aestivum L.) genotype Zlata. The treatment with Au-NPs improved tolerance to low temperatures in control conditions and after cold hardening. Au-NPs treatment boosted the intensity of growth processes, the quantity of photosynthetic pigments, sucrose in leaves, and the expressions of encoded RuBisCo and Wcor15 genes. The potential mechanisms of Au-NPs' influence on the cold tolerance of wheat varieties were considered.

A rapid return to normal: temporal gene expression patterns following cold exposure in the bumble bee Bombus impatiens.

Bumble bees are common in cooler climates and many species likely experience periodic exposure to very cold temperatures, but little is known about the temporal dynamics of cold response mechanisms following chill exposure, especially how persistent effects of cold exposure may facilitate tolerance of future events. To investigate molecular processes involved in the temporal response by bumble bees to acute cold exposure, we compared mRNA transcript abundance in Bombus impatiens workers exposed to 0°C for 75 min (inducing chill coma) and control bees maintained at a constant ambient temperature (28°C). We sequenced the 3' end of mRNA transcripts (TagSeq) to quantify gene expression in thoracic tissue of bees at several time points (0, 10, 30, 120 and 720 min) following cold exposure. Significant differences from control bees were only detectable within 30 min after the treatment, with most occurring at the 10min recovery time point. Genes associated with gluconeogenesis and glycolysis were most notably upregulated, while genes related to lipid and purine metabolism were downregulated. The observed patterns of expression indicate a rapid recovery after chill coma, suggesting an acute differential transcriptional response during recovery from chill coma and return to baseline expression levels within an hour, with no long-term gene expression markers of this cold exposure. Our work highlights the functions and pathways important for acute cold recovery, provides an estimated time frame for recovery from cold exposure in bumble bees, and suggests that cold hardening may be less important for these heterothermic insects.

РАССМОТРЕНИЕ УСТРОЙСТВ И СПОСОБОВ УПРОЧНЕНИЯ ГАЛТЕЛЕЙ ТЕЛ ВРАЩЕНИЯ ППД, ИХ КЛАССИФИКАЦИЯ И РАЗРАБОТКА РЕКОМЕНДАЦИЙ ПО СОВЕРШЕНСТВОВАНИЮ

The service life of heavily loaded shafts is largely determined by the degree of stress in the transition area from one diameter to another. There are a fairly large number of methods for reducing the stress concentration of these areas, but a special place in this case is occupied by strengthening the surfaces of non-profile, heavily loaded shafts. First of all, their fillets are subjected to hardening, which leads to the formation of uniformly distributed compressive stresses in the technological zone and, accordingly, an increase in the fatigue strength of such parts. The method has become especially widespread when hardening crankshafts. Along with this, surface hardening is applied to the abovementioned part to eliminate its bending. This technological process is especially important in the case of restoration of rotating parts. Meanwhile, existing work in this area does not solve existing issues. In this regard, it is necessary to give a critical analysis of the methods and designs for PPD fillets with the development of appropriate proposals, which determines the relevance of the work. The purpose of the study is to consider devices and methods for strengthening fillets of bodies of rotation of PPD, their classification and development of recommendations for improvement. To reveal the goal, the authors conducted a comprehensive review of the information available in the public domain regarding the strengthening of fillets by cold hardening. This made it possible to identify their advantages and disadvantages. First of all, this is the lack of a unified classification system, as well as methods for preventing the formation of a “wave of deformation”. Based on the analysis, a classification is proposed based on the factors that determine the properties of the shafts and the quality of their surface layers and the functional purpose of the processing. A proprietary scheme for processing SPD surfaces is proposed, which ensures the prevention of a “wave of deformation” in one pass of the working tool, which is based on the well-known principles of the theory of the introduction of a ball indenter into a solid.

Temperature-Caused Changes in Raman Pattern and Protein Profiles of Winter Triticale (x Triticosecale, Wittm.) Field-Grown Seedlings.

Climate change, which causes periods with relatively high temperatures in winter in Poland, can lead to a shortening or interruption of the cold hardening of crops. Previous research indicates that cold acclimation is of key importance in the process of acquiring cereal tolerance to stress factors. The objective of this work was to verify the hypothesis that both natural temperature fluctuations and the plant genotype influence the content of metabolites as well as proteins, including antioxidant enzymes and photosystem proteins. The research material involved four winter triticale genotypes, differing in their tolerance to stress under controlled conditions. The values of chlorophyll a fluorescence parameters and antioxidant activity were measured in their seedlings. Subsequently, the contribution of selected proteins was verified using specific antibodies. In parallel, the profiling of the contents of chlorophylls, carotenoids, phenolic compounds, and proteins was carried out by Raman spectroscopy. The obtained results indicate that a better PSII performance along with a higher photosystem II proteins content and thioredoxin reductase abundance were accompanied by a higher antioxidant activity in the field-grown triticale seedlings. The Raman studies showed that the cold hardening led to a variation in photosynthetic dyes and an increase in the phenolic to carotenoids ratio in all DH lines.

Freezing treatment under light conditions leads to a dramatic enhancement of freezing tolerance in cold-acclimated Arabidopsis.

Overwintering plants survive subzero temperatures by cold acclimation (CA), wherein they acquire freezing tolerance through short-term exposure to low temperatures above 0°C. The freezing tolerance of CA plants increases when they are subsequently exposed to mild subzero temperatures, a phenomenon known as second-phase cold hardening (2PH). Here, we explored the molecular mechanism and physiological conditions of 2PH. The results show that, compared with supercooling, a freezing treatment during 2PH after CA enhanced the freezing tolerance of Arabidopsis. This required CA as a pretreatment, and was designated as second-phase freezing acclimation (2PFA). Light increased the effect of 2PFA to enhance freezing tolerance after CA. C-repeat binding factor and cold-regulatedgenes were downregulated by light during the 2PFA treatment, a different transcription profile from that during CA. The freezing tolerance of 2PFA plants was decreased by the presence of the photosynthetic electron transfer inhibitor 3-(3,4-dichlorophenyl)-1,1-dimethylureaduring the 2PFA treatment. Compared with wild-type plants, phototropin1,2 and phyb mutants showed lower freezing tolerance after 2PFA treatment. These results show that exposure to freezing after CA increases freezing tolerance as a secondary process, and that freezing under light conditions further increases freezing tolerance via pathways involving photoreceptors and photosynthetic electron transfer.

Microhardness Profile and Residual Stresses Evaluation in a Shot Peened SAE 5160H Steel

Shot peening (SP) is a surface cold hardening process used on metals to enhance life under cyclic stress. In this case, SP was applied to SAE5160H samples of steel quenched tempered in oil at 460 °C used for leaf springs. This study shows the residual surface stresses measured through X-ray diffraction (XRD) and the microhardness variation through the perpendicular-to-the-peened surface using a combination of metallographic preparation and Vickers microhardness (HVN). This combination of techniques makes possible measuring the SP effect in perpendicular-to-the-treated surface. A residual stress of -365.8 ± 78 MPa measured by XRD and a maximum microhardness of 525± at 92.7 HVN on the surface were obtained for the SP material. Alternatively, an average of 54.2 ± 54.3 MPa residual stress measured by XRD and 433 ± 39.5 HVN were obtained for the As-it-is samples. In addition, corrosion electrochemical potential tests showed that SP increases the corrosion potential, which makes this process undesirable if the SP component is exposed to aggressive environments. Moreover, the As-it-is samples presented not statistically significant HVN difference in the measured points. The combination of experimental techniques allows estimating hardness change in perpendicular-to-the treated surface separated by as little as 10 µm but with a simpler specimen preparation than other techniques such as XRD or strain gauges. Such a combination can be an alternative for estimating residual stresses through depth.

Seasonal Variations in the Toughness of Leaves: A Case Study Using Griselinia littoralis.

Potential effects of climate change include greater extremes of temperature and increased severity of storms. Many plants have evolved to resist the challenges of winter (freezing, dehydration, and wind) in a process known as cold hardening. Sensing reducing temperatures, they make structural changes at the cellular level to increase their mechanical resistance and prevent damage. Previous work on this topic, though extensive, has been conducted under laboratory conditions rather than in the field, and while many workers have observed changes to cell wall thickness and composition, which imply increased mechanical strength, few have actually measured strength or any other parameter describing structural integrity. This paper describes experiments on a model system designed to measure the structural integrity of leaf laminae from plants growing naturally in the field over extended periods, allowing seasonal variations to be captured. Standard engineering properties-tensile strength and fracture toughness-were measured for leaves of Griselinia littoralis on 19 separate occasions over a 12-month period. Toughness (rather than strength) was found to be the controlling mechanical property. Toughness values were found to change significantly during the year, by more than a factor of 2. Toughness correlated strongly with average daily soil temperature, but with a lag of about 1-2 weeks, suggesting that this is the time needed for structural adjustments to take place. Highest toughness values occurred in winter, confirming cold hardening. Increasing temperature in the spring was associated with decreasing toughness, but in the summer, when highest temperatures occurred, toughness increased again. This apparent "hot hardening" may be a response to dehydration. Results imply that a given leaf is able to both increase and decrease its toughness in response to temperature changes, demonstrating excellent plasticity of response. This case study of a single species establishes a method of reliably measuring changes in a plant's structural integrity due to cold hardening and other seasonal variations, which may be used to investigate the effects of climate change and other variables.

Metabolites, ions, and the mechanisms behind seasonal cold hardening of Pyrochroa coccinea (Pyrochroidae) larvae

The larvae of the black headed cardinal beetle Pyrochroa coccinea, overwinters under the bark of dead logs in northern European dioecious forests, and are thus exposed to temperatures below the melting point of their bodily fluids. Here we explore the mechanisms behind their seasonal cold hardening by characterising field samples collected monthly throughout the year. Both the lower lethal temperature and supercooling point dropped as much as 10℃ in the second half of November, reaching values around –15℃ by the beginning of December. This change was accompanied by a 320 mosmol/kg increase in hemolymph osmolality, which is a doubling compared to the summer levels. We used NMR metabolomics to identify and measure the absolute concentrations of the responsible cryoprotective C-H containing metabolites in the hemolymph. The largest increase was found to be in either glucose or trehalose, with an average total increase of 120 mM. Proline, alanine, and choline concentrations were found to increase by around 10 mM each. Contrarily, phosphocholine and phosphoethanolamine were halved, resulting in a total decrease of around 50 mM. These measurements were complemented with ion exchange chromatography measurements. This allowed us to account for all the osmotic pressure in the summer hemolymph, and the measured concentration changes explained as much as 40 % of the observed osmolality increase upon cold hardening. Preliminary results indicate that the remainder may be explained by non-colligative protein contributions.

Trehalose-6-Phosphate Synthase Contributes to Rapid Cold Hardening in the Invasive Insect Lissorhoptrus oryzophilus (Coleoptera: Curculionidae) by Regulating Trehalose Metabolism.

Rapid cold hardening (RCH) is known to rapidly enhance the cold tolerance of insects. Trehalose has been demonstrated to be a cryoprotectant in Lissorhoptrus oryzophilus, an important invasive pest of rice in China. Trehalose synthesis mainly occurs through the Trehalose-6-phosphate synthase (TPS)/trehalose-6-phosphate phosphatase (TPP) pathway in insects. In this study, the TPS gene from L. oryzophilus (LoTPS) was cloned and characterized for the first time. Its expression and trehalose content changes elicited by RCH were investigated. Our results revealed that RCH not only increased the survival rate of adults but also upregulated the expression level of LoTPS and increased the trehalose content under low temperature. We hypothesized that upregulated LoTPS promoted trehalose synthesis and accumulation to protect adults from low-temperature damage. To further verify the function of the LoTPS gene, we employed RNA interference (RNAi) technology. Our findings showed that RCH efficiency disappeared and the survival rate did not increase when the adults were fed dsRNA of LoTPS. Additionally, inhibiting LoTPS expression resulted in no significant difference in trehalose content between the RCH and non-RCH treatments. Furthermore, the expression patterns of trehalose transporter (TRET) and trehalase (TRE) were also affected. Collectively, these results indicate the critical role of LoTPS in L. oryzophilus cold resistance after RCH induction. LoTPS can enhance survival ability by regulating trehalose metabolism. These findings contribute to further understanding the role of TPS in insect cold resistance and the invasiveness of L. oryzophilus. Moreover, RNAi of LoTPS opens up possibilities for novel control strategies against L. oryzophilus in the future.

Rapid cold hardening modifies ion regulation to delay anoxia-induced spreading depolarization in the CNS of the locust

Insects experience different kinds of environmental stresses that can impair neural performance, leading to spreading depolarization (SD) of nerve cells and neural shutdown underlying coma. SD is associated with a sudden loss of ion, notably K+, homeostasis in the central nervous system. The sensitivity of an insect's nervous system to stress (e.g., anoxia) can be modulated by acute pre-treatment. Rapid cold hardening (RCH) is a form of preconditioning, in which a brief exposure to low temperature can enhance the stress tolerance of insects. We used a pharmacological approach to investigate whether RCH affects anoxia-induced SD in the locust, Locusta migratoria, via one or more of the following homeostatic mechanisms: (1) Na+/K+-ATPase (NKA), (2) Na+/K+/2Cl− co-transporter (NKCC), and (3) voltage-gated K+ (Kv) channels. We also assessed abundance and phosphorylation of NKCC using immunoblotting. We found that inhibition of NKA or Kv channels delayed the onset of anoxia-induced SD in both control and RCH preparations. However, NKCC inhibition preferentially abrogated the effect of RCH. Additionally, we observed a higher abundance of NKCC in RCH preps but no statistical difference in its phosphorylation level, indicating the involvement of NKCC expression or degradation as part of the RCH mechanism.

Study of the Effect of Mowing and Drying on the Lipid Composition of Grass Leaves in Permafrost Ecosystems

Mowing the plant shoots under hot, sunny, and dry conditions severely traumatizes the entire vegetative body, and the overall life cycle of the plant is altered. The purpose of the present research was to investigate the effects of mowing and drying on lipids, fatty acids (FA), sterols, and the systemic responses in leaves of plant material at three time points (24 h, 72 h, and leaves of new shoots after traumatic mowing in summer (1 July) and those subjected to cold hardening by autumn temperatures in September (aftergrass)) were analyzed for the first time. The leaves of five species of herbaceous plants growing in permafrost ecosystems were analyzed by HPTLC and GC-MS. It was established that fatty acids in the tissues of aftergrass leaves were characterized by higher values of the n-6/n-3 ratio than in summer grasses. It was demonstrated that exposure of leaves for 72 h in natural conditions in summer and at low temperatures in autumn in leaves of aftergrass resulted in significant changes in the composition of membrane phospholipids. The obtained findings indicate that leaves of aftergrass are the most valuable plant raw material in terms of FAs and phytosterols content compared to hay mowed in summer.

Off-host survival of Dermacentor variabilis (Acari: Ixodidae) adults near their northern distributional limit in Saskatchewan, Canada.

Dermacentor variabilis (Say) is expanding its range northwards in Saskatchewan and Manitoba (Canada). Knowledge of the relative ability of different life cycle stages to survive off-host over winter is important for assessing the potential for further range expansion and risk of pathogen transmission. In the present study, the off-host survival of D. variabilis adults was determined in outdoor terraria within a field plot close to Lizard Lake Community Pasture (LLCP) situated near the northern distributional limit in Saskatchewan. Only a small proportion (7%) of adult ticks in this relatively recently established population survived from mid-summer to late winter. Off-host survival had declined further to <4% by mid-spring. A significantly greater proportion of female ticks (6%) survived from mid-summer to mid-spring than did male ticks (1%). The supercooling points (SCPs), the temperature below 0 °C when body fluids spontaneously freeze, of the 17 ticks that survived through to mid-spring did not differ significantly from the SCPs of questing ticks in the previous summer, suggesting adult D. variabilis do not undergo cold hardening during winter diapause. The off-host survival of D. variabilis adults near LLCP was also much lower than that previously reported for adults from Sandy Hook in Manitoba, a population that has been established for decades. This finding suggests that there is geographical variation in the ability of D. variabilis in southern Canada to survive from mid-summer to the subsequent spring. However, the ecological and genetic factors influencing the survival of northern populations of D. variabilis requires further investigation.

The effect of laser shock peening on very high cycle fatigue properties of laser welded 2A60 aluminum alloy joints

Laser shock peening (LSP) technology has the advantages of deep residual compressive stress field, low degree of cold hardening and controllable hardening area. The surface modification of welded structures has broad prospects. To predict the very high cycle fatigue (VHCF) life of an aero engine impeller, it is of great engineering significance to study the VHCF performance of 2A60 aluminum alloy. The effects of LSP on VHCF properties of laser welded joints were investigated from the S-N curve, fracture morphology, residual stress, hardness, and roughness. The results show that the S-N curves of the 2A60 aluminum alloy matrix under the condition of ethanol cooling belong to the infinite life type. The S-N curves of welded and LSP samples belong to the continuous decline type. In the process of LSP, the fatigue crack source is transferred from the surface of the sample to the second surface of the sample, which not only counteracts the residual tensile stress introduced on the surface of the sample during welding but also introduces considerable residual compressive stress on the surface of the sample. The roughness is reduced, thus improving the fatigue stsample's fatigue strength and life. The strengthening mechanism of LSP is discussed from two aspects of dislocation strengthening and residual stress. The LSP results in many dislocation proliferation within the grain, and the dislocation entanglement and dislocation wall are formed among the dislocations. The original coarse crystal is divided into multiple subgrains to achieve the effect of grain refinement. Grain refinement and high-density dislocation increase the hardness of the material.