Recent advances in deep learning have significantly improved image deblurring;however,existing approaches still suffer from limited global context modeling,inadequate detail restoration,and poor texture or edge percep...Recent advances in deep learning have significantly improved image deblurring;however,existing approaches still suffer from limited global context modeling,inadequate detail restoration,and poor texture or edge perception,especially under complex dynamic blur.To address these challenges,we propose the Multi-Resolution Fusion Network(MRFNet),a blind multi-scale deblurring framework that integrates progressive residual connectivity for hierarchical feature fusion.The network employs a three-stage design:(1)TransformerBlocks capture long-range dependencies and reconstruct coarse global structures;(2)Nonlinear Activation Free Blocks(NAFBlocks)enhance local detail representation and mid-level feature fusion;and(3)an optimized residual subnetwork based on gated feature modulation refines texture and edge details for high-fidelity restoration.Extensive experiments demonstrate that MRFNet achieves superior performance compared to state-of-the-art methods.On GoPro,it attains 32.52 dB Peak Signal-to-Noise Ratio(PSNR)and 0.071 Learned Perceptual Image Patch Similarity(LPIPS),outperforming MIMOWNet(32.50 dB,0.075).On HIDE,it achieves 30.25 dB PSNR and 0.945 Structural Similarity Index Measure(SSIM),representing gains of+0.26 dB and+0.015 SSIM over MIMO-UNet(29.99 dB,0.930).On RealBlur-J,it reaches 28.82 dB PSNR and 0.872 SSIM,surpassing MIMO-UNet by+1.19 dB and+0.035 SSIM(27.63 dB,0.837).These results validate the effectiveness of the proposed progressive residual fusion and hybrid attention mechanisms in balancing global context understanding and local detail recovery for blind image deblurring.展开更多
Active inflammation in“inactive”progressive multiple sclerosis:Traditionally,the distinction between relapsing-remitting multiple sclerosis and progressive multiple sclerosis(PMS)has been framed as an inflammatory v...Active inflammation in“inactive”progressive multiple sclerosis:Traditionally,the distinction between relapsing-remitting multiple sclerosis and progressive multiple sclerosis(PMS)has been framed as an inflammatory versus degenerative dichotomy.This was based on a broad misconception regarding essentially all neurodegenerative conditions,depicting the degenerative process as passive and immune-independent occurring as a late byproduct of active inflammation in the central nervous system(CNS),which is(solely)systemically driven.展开更多
The mining industry is frequently subjected to various disasters,one of the major concerns is water-related disasters,particularly seam floor water inrush.These disasters pose significant threats to the safety and pro...The mining industry is frequently subjected to various disasters,one of the major concerns is water-related disasters,particularly seam floor water inrush.These disasters pose significant threats to the safety and production of deep coal mines.The primary reason for this is that the fracturing of the rock mass induces the formation of a fluid(water)with both kinetic and potential energy.In this paper,a novel water inrush mechanism for deep floor failure due to water hammer effects is proposed based on the Xingdong coal mine in China.The water hammer pressure within rock pore channels has a different impact on the surrounding rock,leading to the degradation of the rock mass channel through repeated conduction and instantaneous cutoff.To further investigate this phenomenon,a progressive corrosion fracture mechanics(PCFM)model induced by a water hammer is established.The results show that the water hammer pressure caused by instantaneous channel truncation increases with increasing water flow velocity.The chemical damage factor(i.e.,stress corrosion fracture)is also incorporated into the Dugdale-Barenblatt(D-B)model to analyze the factors influencing the PCFM.These findings indicate that the greater the degree of damage is,the more likely the concealed fault is to experience water inrush.Finally,methods for controlling water inrush caused by the water hammer effects of deep floors are proposed.The failure mechanisms of the water hammer and the PCFM provide theoretical and practical guidance for controlling water inrush from the deep floor.展开更多
Reservoir-induced landslides in China's Three Gorges Reservoir area are prone to tensile cracks due to the influenceof their own weight and fluctuationsin water levels.The presence of cracks indicates that the ten...Reservoir-induced landslides in China's Three Gorges Reservoir area are prone to tensile cracks due to the influenceof their own weight and fluctuationsin water levels.The presence of cracks indicates that the tensile stress in the area has exceeded the tensile strength of the soil,leading to local instability.To explore the impact of tensile failure behavior on the stability and failure modes of reservoir landslides,the Huangtupo Riverside Slump#1 is taken as a case study.By considering local tensile failure,potential tensile cracks are incorporated into the analysis via the limit equilibrium method and reliability theory.The reliability of landslides under different tensile failure scenarios is quantified.Strain-softening characteristics of the soil are combined to further analyze the failure transmission path of the landslide.Finally,these potential failure modes were validated through physical model tests.The results show that cracks developing at rear positions reduce the stability of the slope and increase the probability of instability.During the destruction process,retrogressive failures with multiple sliding surfaces are likely to occur.However,tensile failure at the forefront reduces the likelihood of an individual slide mass descending.Progressive failure results in both regular and skip transmission patterns.Additionally,cracks and water level changes can also lead to shifts in the positions of the most dangerous blocks.Therefore,in practical landslide analysis and prevention,it is necessary to consider local tensile damage and identify potential tensile crack locations in advance to optimize prevention measures and accurately evaluate landslide risk.展开更多
Fine-scale structures can be observed in small field-of-view(FOV)auroral observations,but they are often overlooked because they appear only sporadically in all-sky observations.Such forms are of great interest becaus...Fine-scale structures can be observed in small field-of-view(FOV)auroral observations,but they are often overlooked because they appear only sporadically in all-sky observations.Such forms are of great interest because they may embody specific magnetosphere-ionosphere coupling processes,reveal localized energy deposition pathways,and provide new insights into cross-scale plasma dynamics and instabilities.However,their limited spatial extent,transient occurrence,and scarcity in wide-FOV observations make systematic investigation challenging.Traditional manual analysis struggles to capture these subtle structures within vast all-sky datasets,while automated detection faces severe data imbalance and morphological ambiguity.To address these challenges,we propose a synthetic-to-real progressive learning framework for cross-FOV retrieval of rare auroral forms.A Generative Adversarial Network(GAN)is employed to perform cross-FOV transformation between unpaired small-FOV images containing rare aurora forms and all-sky images(ASI)without such structures,thereby generating large numbers of synthetic ASI with rare auroral morphology.These synthetic samples are used to train an initial detection model,which subsequently undergoes iterative fine-tuning through feedback-guided learning:The model performs inference on new all-sky data,and the progressively accumulated real detections are incorporated into the training set.Experimental results demonstrate that the proposed method achieves over 92%detection accuracy on ASI,enabling high-precision retrieval of small-scale auroral structures across large-scale observations.This framework provides a scalable and effective approach to rediscovering rare auroral phenomena in continuous all-sky monitoring,offering new opportunities for exploring the fine-scale dynamics of the upper atmosphere.展开更多
The microstructural evolution of a cold-rolled and intercritical annealed medium-Mn steel(Fe-0.10C-5Mn)was investigated during uniaxial tensile testing.In-situ observations under scanning electron microscopy,transmiss...The microstructural evolution of a cold-rolled and intercritical annealed medium-Mn steel(Fe-0.10C-5Mn)was investigated during uniaxial tensile testing.In-situ observations under scanning electron microscopy,transmission electron microscopy,and X-ray diffraction analysis were conducted to characterize the progressive transformation-induced plasticity process and associated fracture initiation mechanisms.These findings were discussed with the local strain measurements via digital image correlation.The results indicated that Lüders band formation in the steel was limited to 1.5%strain,which was mainly due to the early-stage martensitic phase transformation of a very small amount of the less stable large-sized retained austenite(RA),which led to localized stress concentrations and strain hardening and further retardation of yielding.The small-sized RA exhibited high stability and progressively transformed into martensite and contributed to a stably extended Portevin-Le Chatelier effect.The volume fraction of RA gradually decreased from 26.8%to 8.2%prior to fracture.In the late deformation stage,fracture initiation primarily occurred at the austenite/martensite and ferrite/martensite interfaces and the ferrite phase.展开更多
The progressive failure characteristics of geomaterial are a remarkable and challenging topic in geotechnical engineering.To study the effect of salt content and temperature on the progressive failure characteristics ...The progressive failure characteristics of geomaterial are a remarkable and challenging topic in geotechnical engineering.To study the effect of salt content and temperature on the progressive failure characteristics of frozen sodium sulfate saline sandy soil,a series of uniaxial compression tests were performed by integrating digital image correlation(DIC)technology into the testing apparatus.The evolution law of the uniaxial compression strength(UCS),the failure strain,and the formation of the shear band of the frozen sodium sulfate saline sandy soil were analyzed.The test results show that within the scope of this study,with the increase of salt content,both the UCS and the shear band angle initially decrease with increasing salt content before showing an increase.In contrast,the failure strain and the width of the shear band exhibit an initial increase followed by a decrease in the samples.In addition,to investigate the brittle failure characteristics of frozen sodium sulfate saline sandy soil,two classic brittleness evaluation methods were employed to quantitatively assess the brittleness level for the soil samples.The findings suggest that the failure characteristics under all test conditions in this study belong to the transition stage between brittle and ductile,indicating that frozen sodium sulfate saline sandy soil exhibits certain brittle behavior under uniaxial compression conditions,and the brittleness index basically decreases and then increases with the rise in salt content.展开更多
A new extended distribution called the Odd Exponential Generalized Exponential-Exponential distribution(EOEGE-E)is proposed based on generalization of the odd generalized exponential family(OEGE-E).The statistical pro...A new extended distribution called the Odd Exponential Generalized Exponential-Exponential distribution(EOEGE-E)is proposed based on generalization of the odd generalized exponential family(OEGE-E).The statistical properties of the proposed distribution are derived.The study evaluates the accuracy of six estimation methods under complete samples.Estimation techniques include maximumlikelihood,ordinary least squares,weighted least squares,maximumproduct of spacing,Cramer vonMises,and Anderson-Darling methods.Twomethods of estimation for the involved parameters are considered based on progressively type Ⅱ censored data(PTⅡC).These methods are maximum likelihood and maximum product of spacing.The proposed distribution’s effectiveness was evaluated using different data sets from various fields.The proposed distribution provides a better fit for these datasets than existing probability distributions.展开更多
Background Progressive oxidative stress easily occurs as a result of a gradual increase in the intensity of maternal metabolism due to rapid foetal development and increased intensity of lactation.However,studies on t...Background Progressive oxidative stress easily occurs as a result of a gradual increase in the intensity of maternal metabolism due to rapid foetal development and increased intensity of lactation.However,studies on the effects of processive oxidative stress on nutrient transport in the placenta have received little attention.The present study was conducted on sows at 85 days of gestation to study the effects of pterostilbene(PTE)on maternal oxidative stress status and placental nutrient transport.Results PTE increased the antioxidant capacity and immunoglobulin content in mothers’blood and milk,reduced the level of inflammatory factors,and improved the nutrient content of milk.PTE also reduced sow backfat loss and the number of weak sons,and increased piglet weaning weight and total weaning litter weight.We subsequently found that PTE enhanced placental glucose and fatty acid transport and further affected glycolipid metabolism by increasing the expression of LAL,PYGM,and Gbe-1,which activated the PI3K phosphorylation pathway.Moreover,PTE addition altered the relative abundance of the Firmicutes,Proteobacteria,Parabacillus,and Bacteroidetes-like RF16 groups in sow faeces.PTE increased the levels of acetate,propionate,butyrate and isovalerate in the faeces.Conclusions These findings reveal that the addition of PTE during pregnancy and lactation mitigates the effects of processive oxidative stress on offspring development by altering maternal microbial and placental nutrient trans-port capacity.展开更多
High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock inst...High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock instability,yet the fracture mechanisms and load response relationships remain poorly understood.This study prepared intact and fractured sandstone specimens,subjected them to F-T cycles and graded loading-unloading,and monitored their structural evolution via X-ray computed tomography.First,the progressive failure process was investigated from both qualitative morphologic features and quantitative void parameters.The results showed that intact and fractured sandstone instability behaviors are determined by F-T damage and joint arrangement,respectively.However,both indicate that precursory localization of failure can only be detected when heterogeneous damage exists in advance.Furthermore,the void parameters of undamaged intact sandstone exhibit power-law acceleration,while damaged sandstones are characterized by a trend of initial decrease followed by an increase.Subsequently,a damage constitutive model for freeze-thawed fractured sandstone under graded loading-unloading was established.This model is based on the Lemaitre strain equivalence hypothesis and defines the coupled damage variable through multivariable indicators.In this framework,the material damage induced by fractures and F-T is unified and characterized by void parameters;while the load-induced damage is integrated with the energy linear allocation law and defined by damage energy.Thus,the stress-strain theoretical relationship is depicted,and the model is validated as reliable.Finally,a conceptual model of rock damage due to F-T and loading-unloading was proposed by combining the microscopic testing results from X-ray diffraction and scanning electron microscopy.展开更多
基金funded by Qinghai University Postgraduate Research and Practice Innovation Program of Funder,grant number 2025-GMKY-42.
文摘Recent advances in deep learning have significantly improved image deblurring;however,existing approaches still suffer from limited global context modeling,inadequate detail restoration,and poor texture or edge perception,especially under complex dynamic blur.To address these challenges,we propose the Multi-Resolution Fusion Network(MRFNet),a blind multi-scale deblurring framework that integrates progressive residual connectivity for hierarchical feature fusion.The network employs a three-stage design:(1)TransformerBlocks capture long-range dependencies and reconstruct coarse global structures;(2)Nonlinear Activation Free Blocks(NAFBlocks)enhance local detail representation and mid-level feature fusion;and(3)an optimized residual subnetwork based on gated feature modulation refines texture and edge details for high-fidelity restoration.Extensive experiments demonstrate that MRFNet achieves superior performance compared to state-of-the-art methods.On GoPro,it attains 32.52 dB Peak Signal-to-Noise Ratio(PSNR)and 0.071 Learned Perceptual Image Patch Similarity(LPIPS),outperforming MIMOWNet(32.50 dB,0.075).On HIDE,it achieves 30.25 dB PSNR and 0.945 Structural Similarity Index Measure(SSIM),representing gains of+0.26 dB and+0.015 SSIM over MIMO-UNet(29.99 dB,0.930).On RealBlur-J,it reaches 28.82 dB PSNR and 0.872 SSIM,surpassing MIMO-UNet by+1.19 dB and+0.035 SSIM(27.63 dB,0.837).These results validate the effectiveness of the proposed progressive residual fusion and hybrid attention mechanisms in balancing global context understanding and local detail recovery for blind image deblurring.
文摘Active inflammation in“inactive”progressive multiple sclerosis:Traditionally,the distinction between relapsing-remitting multiple sclerosis and progressive multiple sclerosis(PMS)has been framed as an inflammatory versus degenerative dichotomy.This was based on a broad misconception regarding essentially all neurodegenerative conditions,depicting the degenerative process as passive and immune-independent occurring as a late byproduct of active inflammation in the central nervous system(CNS),which is(solely)systemically driven.
基金supported by the National Natural Science Foundation of China(Grant Nos.52225404 and 52404121)the Key Research and Development Program Projects of Xinjiang Uygur Autonomous Region(Grant No.2024B03017).
文摘The mining industry is frequently subjected to various disasters,one of the major concerns is water-related disasters,particularly seam floor water inrush.These disasters pose significant threats to the safety and production of deep coal mines.The primary reason for this is that the fracturing of the rock mass induces the formation of a fluid(water)with both kinetic and potential energy.In this paper,a novel water inrush mechanism for deep floor failure due to water hammer effects is proposed based on the Xingdong coal mine in China.The water hammer pressure within rock pore channels has a different impact on the surrounding rock,leading to the degradation of the rock mass channel through repeated conduction and instantaneous cutoff.To further investigate this phenomenon,a progressive corrosion fracture mechanics(PCFM)model induced by a water hammer is established.The results show that the water hammer pressure caused by instantaneous channel truncation increases with increasing water flow velocity.The chemical damage factor(i.e.,stress corrosion fracture)is also incorporated into the Dugdale-Barenblatt(D-B)model to analyze the factors influencing the PCFM.These findings indicate that the greater the degree of damage is,the more likely the concealed fault is to experience water inrush.Finally,methods for controlling water inrush caused by the water hammer effects of deep floors are proposed.The failure mechanisms of the water hammer and the PCFM provide theoretical and practical guidance for controlling water inrush from the deep floor.
基金supported by the Major Program of National Natural Science Foundation of China(Grant No.42090055)the National Key ScientificInstruments and Equipment Development Projects of China(Grant No.41827808)the National Nature Science Foundation of China(Grant No.42207216).
文摘Reservoir-induced landslides in China's Three Gorges Reservoir area are prone to tensile cracks due to the influenceof their own weight and fluctuationsin water levels.The presence of cracks indicates that the tensile stress in the area has exceeded the tensile strength of the soil,leading to local instability.To explore the impact of tensile failure behavior on the stability and failure modes of reservoir landslides,the Huangtupo Riverside Slump#1 is taken as a case study.By considering local tensile failure,potential tensile cracks are incorporated into the analysis via the limit equilibrium method and reliability theory.The reliability of landslides under different tensile failure scenarios is quantified.Strain-softening characteristics of the soil are combined to further analyze the failure transmission path of the landslide.Finally,these potential failure modes were validated through physical model tests.The results show that cracks developing at rear positions reduce the stability of the slope and increase the probability of instability.During the destruction process,retrogressive failures with multiple sliding surfaces are likely to occur.However,tensile failure at the forefront reduces the likelihood of an individual slide mass descending.Progressive failure results in both regular and skip transmission patterns.Additionally,cracks and water level changes can also lead to shifts in the positions of the most dangerous blocks.Therefore,in practical landslide analysis and prevention,it is necessary to consider local tensile damage and identify potential tensile crack locations in advance to optimize prevention measures and accurately evaluate landslide risk.
基金supported by the National Natural Science Foundation of China(Grant no.41874173).
文摘Fine-scale structures can be observed in small field-of-view(FOV)auroral observations,but they are often overlooked because they appear only sporadically in all-sky observations.Such forms are of great interest because they may embody specific magnetosphere-ionosphere coupling processes,reveal localized energy deposition pathways,and provide new insights into cross-scale plasma dynamics and instabilities.However,their limited spatial extent,transient occurrence,and scarcity in wide-FOV observations make systematic investigation challenging.Traditional manual analysis struggles to capture these subtle structures within vast all-sky datasets,while automated detection faces severe data imbalance and morphological ambiguity.To address these challenges,we propose a synthetic-to-real progressive learning framework for cross-FOV retrieval of rare auroral forms.A Generative Adversarial Network(GAN)is employed to perform cross-FOV transformation between unpaired small-FOV images containing rare aurora forms and all-sky images(ASI)without such structures,thereby generating large numbers of synthetic ASI with rare auroral morphology.These synthetic samples are used to train an initial detection model,which subsequently undergoes iterative fine-tuning through feedback-guided learning:The model performs inference on new all-sky data,and the progressively accumulated real detections are incorporated into the training set.Experimental results demonstrate that the proposed method achieves over 92%detection accuracy on ASI,enabling high-precision retrieval of small-scale auroral structures across large-scale observations.This framework provides a scalable and effective approach to rediscovering rare auroral phenomena in continuous all-sky monitoring,offering new opportunities for exploring the fine-scale dynamics of the upper atmosphere.
基金supported by the National Key R&D Program of China(No.2017YFB0304402)。
文摘The microstructural evolution of a cold-rolled and intercritical annealed medium-Mn steel(Fe-0.10C-5Mn)was investigated during uniaxial tensile testing.In-situ observations under scanning electron microscopy,transmission electron microscopy,and X-ray diffraction analysis were conducted to characterize the progressive transformation-induced plasticity process and associated fracture initiation mechanisms.These findings were discussed with the local strain measurements via digital image correlation.The results indicated that Lüders band formation in the steel was limited to 1.5%strain,which was mainly due to the early-stage martensitic phase transformation of a very small amount of the less stable large-sized retained austenite(RA),which led to localized stress concentrations and strain hardening and further retardation of yielding.The small-sized RA exhibited high stability and progressively transformed into martensite and contributed to a stably extended Portevin-Le Chatelier effect.The volume fraction of RA gradually decreased from 26.8%to 8.2%prior to fracture.In the late deformation stage,fracture initiation primarily occurred at the austenite/martensite and ferrite/martensite interfaces and the ferrite phase.
基金supported by the National Natural Science Foundation of China(Grant Nos.42372312,and 42172299)the Pyramid Talent Training Project of Beijing University of Civil Engineering and Architecture(Grant No.JDYC20220807).
文摘The progressive failure characteristics of geomaterial are a remarkable and challenging topic in geotechnical engineering.To study the effect of salt content and temperature on the progressive failure characteristics of frozen sodium sulfate saline sandy soil,a series of uniaxial compression tests were performed by integrating digital image correlation(DIC)technology into the testing apparatus.The evolution law of the uniaxial compression strength(UCS),the failure strain,and the formation of the shear band of the frozen sodium sulfate saline sandy soil were analyzed.The test results show that within the scope of this study,with the increase of salt content,both the UCS and the shear band angle initially decrease with increasing salt content before showing an increase.In contrast,the failure strain and the width of the shear band exhibit an initial increase followed by a decrease in the samples.In addition,to investigate the brittle failure characteristics of frozen sodium sulfate saline sandy soil,two classic brittleness evaluation methods were employed to quantitatively assess the brittleness level for the soil samples.The findings suggest that the failure characteristics under all test conditions in this study belong to the transition stage between brittle and ductile,indicating that frozen sodium sulfate saline sandy soil exhibits certain brittle behavior under uniaxial compression conditions,and the brittleness index basically decreases and then increases with the rise in salt content.
文摘A new extended distribution called the Odd Exponential Generalized Exponential-Exponential distribution(EOEGE-E)is proposed based on generalization of the odd generalized exponential family(OEGE-E).The statistical properties of the proposed distribution are derived.The study evaluates the accuracy of six estimation methods under complete samples.Estimation techniques include maximumlikelihood,ordinary least squares,weighted least squares,maximumproduct of spacing,Cramer vonMises,and Anderson-Darling methods.Twomethods of estimation for the involved parameters are considered based on progressively type Ⅱ censored data(PTⅡC).These methods are maximum likelihood and maximum product of spacing.The proposed distribution’s effectiveness was evaluated using different data sets from various fields.The proposed distribution provides a better fit for these datasets than existing probability distributions.
基金Natural Science Foundation of Heilongjiang Province(YQ2022C014)National Natural Science Foundation of China(32302768).
文摘Background Progressive oxidative stress easily occurs as a result of a gradual increase in the intensity of maternal metabolism due to rapid foetal development and increased intensity of lactation.However,studies on the effects of processive oxidative stress on nutrient transport in the placenta have received little attention.The present study was conducted on sows at 85 days of gestation to study the effects of pterostilbene(PTE)on maternal oxidative stress status and placental nutrient transport.Results PTE increased the antioxidant capacity and immunoglobulin content in mothers’blood and milk,reduced the level of inflammatory factors,and improved the nutrient content of milk.PTE also reduced sow backfat loss and the number of weak sons,and increased piglet weaning weight and total weaning litter weight.We subsequently found that PTE enhanced placental glucose and fatty acid transport and further affected glycolipid metabolism by increasing the expression of LAL,PYGM,and Gbe-1,which activated the PI3K phosphorylation pathway.Moreover,PTE addition altered the relative abundance of the Firmicutes,Proteobacteria,Parabacillus,and Bacteroidetes-like RF16 groups in sow faeces.PTE increased the levels of acetate,propionate,butyrate and isovalerate in the faeces.Conclusions These findings reveal that the addition of PTE during pregnancy and lactation mitigates the effects of processive oxidative stress on offspring development by altering maternal microbial and placental nutrient trans-port capacity.
基金supported by the National Natural Science Foundation of China(Grant Nos.11972283 and 42277182).
文摘High-altitude cold regions exhibit complex geological and environmental conditions,fostering steep rock slopes with macroscopic joints and mesoscopic freeze-thaw(F-T)damage.Cyclic loading further exacerbates rock instability,yet the fracture mechanisms and load response relationships remain poorly understood.This study prepared intact and fractured sandstone specimens,subjected them to F-T cycles and graded loading-unloading,and monitored their structural evolution via X-ray computed tomography.First,the progressive failure process was investigated from both qualitative morphologic features and quantitative void parameters.The results showed that intact and fractured sandstone instability behaviors are determined by F-T damage and joint arrangement,respectively.However,both indicate that precursory localization of failure can only be detected when heterogeneous damage exists in advance.Furthermore,the void parameters of undamaged intact sandstone exhibit power-law acceleration,while damaged sandstones are characterized by a trend of initial decrease followed by an increase.Subsequently,a damage constitutive model for freeze-thawed fractured sandstone under graded loading-unloading was established.This model is based on the Lemaitre strain equivalence hypothesis and defines the coupled damage variable through multivariable indicators.In this framework,the material damage induced by fractures and F-T is unified and characterized by void parameters;while the load-induced damage is integrated with the energy linear allocation law and defined by damage energy.Thus,the stress-strain theoretical relationship is depicted,and the model is validated as reliable.Finally,a conceptual model of rock damage due to F-T and loading-unloading was proposed by combining the microscopic testing results from X-ray diffraction and scanning electron microscopy.
