Moisture-induced Stresses Research Articles

Evaluation of Moisture-Induced Stresses in Wood Cross-Sections Determined with a Time-Dependent, Plastic Material Model during Long-Time Exposure

In recent years, the use of timber as a building material in larger construction applications such as multi-story buildings and bridges has increased. This requires a better understanding of the material to realize such constructions and design them more economically. However, accurate computational simulations of timber structures are challenging due to the complexity and inhomogeneity of this naturally grown material. It exhibits growth inhomogeneities such as knots and fiber deviations, orthotropic material behavior and moisture dependence of almost all physical parameters. Describing the creep response of wood under real climate conditions is particularly difficult. Changes in moisture content, plasticity and viscoelasticity affect moisture-induced stresses and potentially lead to cracks and structural damage. In this paper, we apply a material model that combines time and moisture-dependent behavior with multisurface plasticity to simulate cross-sections of different dimensions over a 14-month climate period. Our findings indicate that considering this long-term behavior has a minor impact on moisture-induced stresses during the drying period. However, during the wetting period, neglecting the time- and moisture-dependent material behavior of wood leads to a significant overestimation of tensile stresses within the cross-section, resulting in unrealistic predictions of wetting-induced fracture. Therefore, simulations during wetting periods require a sophisticated rheological model to properly reproduce the stress field.

Analysis of Pore Water Pressure Effect in Asphalt Patch Failure: An Integrated Modelling and Experiment Study

Moisture has been widely accepted as the main cause of asphalt patch failure, while the investigation of pore water pressure (PWP) in asphalt patch is limited. This research investigated the PWP generated in asphalt patch and quantified its impact on mechanical performance considering the inadequate compaction of asphalt patch. A hydro-mechanical model was first developed to analyze the PWP under field conditions, considering the effects of patch geometry, vehicle wandering, traffic loading, and temperature. The moisture-induced stress tester (MIST) was then used to condition patching materials under different PWP levels in a laboratory. After that, indirect tensile (IDT) and interface shear strengths of patching materials were evaluated to quantify the impact of PWP on material degradation. The numerical modeling results show that the maximum PWP can be within or at the interface of the asphalt patch, depending on the wheel path. The magnitude of PWP is related to the patch geometry, traffic load, and temperature. The maximum PWP, whether inside or at the interface of the asphalt patch, can be from 100 kPa to over 300 kPa under common field conditions. The laboratory experimental results suggest that the first 500 cycles of MIST conditioning led to over 30% decrease in both IDT and interface shear strengths of asphalt patch, and the strength ratio was much lower than the recommended level. These findings indicate that asphalt patches with poor compaction quality are very susceptible to moisture-induced damage, and the mechanical performance of patching material should be evaluated after conditioning with PWP effect.

Moisture-induced stresses and damage in adhesively bonded timber-concrete composite connection

An experimental program was conducted to clarify the wood swelling effect on the shear strength and failure modes of adhesively bonded timber-concrete composite (TCC) joints. A total of 150 TCC joints were fabricated and cured in the condition of 20 °C & 55% relative humidity (RH) for one month, then the joints were divided into three groups (50 each group) and treated at 20 °C and 55%, 75%, and 95%RH, respectively. After about 30-, 100-, 200-, 300-, and 390-day treatment, ten samples from each group were tested to determine their shear strength and failure modes. It was found that an increase in moisture content (e.g., by 10.8%) caused a reduction of shear bond strength (e.g., by 25%). Concrete failure was found to be the dominant failure mode for all tested joints. Finite element (FE) analyses were performed to facilitate understanding of the underlying mechanisms of wood swelling effects. When the moisture content of wood increased by 10.8%, the FE analyses showed that the wood swelling resulted in significant internal stresses and concrete tensile damage at the wood/concrete bonding interface, which was the main reason for the reduction of the shear bond strength. In addition, the effects of essential factors, such as material properties of adherents, orientation of wood components relative to the bonding surface, and bonding width perpendicular to the grain direction of wood, on the moisture-induced stresses were studied. Concrete grades hardly had influence. For the bonding process of TCC structure in practice, a smaller orientation angle (i.e., the angle between the radial direction and the bonding surface) is recommended to avoid moisture-induced damage in wood and concrete at their interface. In other words, the surface of a Glulam or CLT product designed for bonding should be as close as possible to R-L planes of the constituent wood blocks and avoid T-L planes. Furthermore, a larger bonding width resulted in higher moisture-induced stresses.

How to regulate moisture-induced stresses in composites: The answer from nanostructure of S2 layer in Wood cell wall

S2 layer of the Wood cell wall is fundamentally a biocomposite with strong hygroscopicity and undergoes significant changes in mechanical properties upon water adsorption. How the internal stress develops during the adsorption process is still unclear. By employing a multi-scale modeling scheme, we successfully resolve the stress distributions within the S2 layer at different moisture levels. We find that the shear stress developed on the fibril-matrix interface is much smaller than that of ordinary fiber-reinforced composites with the same geometrical dimensions due to the heterogeneous nature of the microfibrils. Besides, we demonstrate that the stress developed during dehydration is larger than that during hydration, which is attributed to the fact that the amorphous polymers comprising the matrix suffer from softening upon water adsorption. These unraveled mechanisms can deepen people’s understanding on the origin of the moisture-induced stress in the S2 layer.

Digital image colour analysis to evaluate the moisture sensitivity of hot-mix asphalt mixes

Moisture in hot-mix asphalt (HMA) can cause serious damage such as cracks and ruts if left untreated. This is due to the separation of binder and aggregates caused by moisture-induced stripping. Existing approaches for assessing moisture damage in asphalt are time consuming, destructive and expensive to implement. In contrast, digital image analysis provides a simple, inexpensive and non-destructive method for identifying moisture-sensitive mixes. Colour, as an essential characteristic of an image, effectively conveys information about its content. This study seeks to explore the potential of analysing digital image colour in the L*a*b* colour space to assess the moisture sensitivity of HMA after moisture-induced stress tester conditioning. Laboratory-compacted specimens of loose asphalt mixtures from the field were studied by image processing followed by statistical tests of significance. It is found that two parameters – namely, the ‘average colour value for the L* channel’ and the ‘standard deviation value for the b* channel’ – can be used to distinguish between moisture-sensitive and non-sensitive mixes. The findings of this study suggest that future research may find colour to be a helpful criterion for characterising asphalt materials using digital image processing.

Heat and Moisture Induced Stress and Strain in Wooden Artefacts and Elements in Heritage Buildings: A Review

In the world of cultural heritage, a wide range of artefacts and buildings are made of wood and, therefore, are subjected to moisture-induced stress and strain cycles, owing to environmental fluctuations. Simultaneous action of moisture and mechanical loads lead to a mechanosorptive effect on wood. Therefore, an increase in time-dependent creep, due to mechanical loads, is observed. The assessment of these complex phenomena entails the use of advance and interdisciplinary approaches. Consequently, this article reviews experimental and mathematical methods to study these degradation mechanisms in wooden artefacts and timber elements in heritage buildings. The paper presents the results of a six-step descriptive literature review, providing an overall picture of the ongoing research. Experimental techniques need to be improved so that they are in line with the conservation principles. The combination of experiments and simulations is a reliable predictive approach for better assessing the potential risk damages due to temperature, humidity cycles, and mechanical loads in complex structures. Thus, advanced numerical simulations and mathematical modelling include climate data and experimental measurements. This work also provides an overview of research performed on different categories of cultural heritage characterised by multi-layer structures. The mechanical response to wood–moisture relation is affected by the level of complexity of these structures. Finally, the use of realistic models is limited by knowledge about the material properties and the behaviour of complex structures over time. In addition, research gaps, limitations, and possible future research directions are also provided. This review may represent a starting point for future research on the thermo-hygro-mechanical behaviour of wood heritage.

Prediction of moisture-induced cracks in wooden cross sections using finite element simulations

Wood absorbs and desorbs moisture due to its hygroscopic behavior, leading to moisture gradients in timber elements as well as swelling and shrinkage. These processes are constrained due to the orthotropic material properties of wood, leading to moisture-induced stresses, which can cause crack initiation and propagation. A significant amount of the damage in timber constructions indoors can be related to changes of the moisture content (MC). However, more information is needed about the correlation between moisture changes or gradients and specific damage characteristics, like crack depths. Thus, based on numerical simulations, the crack depth development within two solid timber and one glued laminated timber (GLT) cross section over time for different relative humidity (RH) reductions and initial MCs is analyzed. For this purpose, a multi-Fickian transport model is used to determine moisture fields, which are then used as loads in a subsequent stress simulation, where linear elastic material behavior is considered. An extended finite element approach, supported by a multisurface failure criterion defining the failure behavior, allows for the simulation of moisture-induced discrete cracking. Based on simulation results, correlations between potential maximum crack depths and moisture gradients in indoor climate conditions are derived, which enables the prediction of crack depths in wood. Finally, it is shown that the initial MC level significantly influences the maximum crack depth that can be expected.

Residual stresses in adhesively bonded wood determined by a bilayer flexion reporter system

The application of adhesives in modern timber engineering often introduces moisture into the wood, leading to permanent residual stresses after hardening. This paper proposes a novel approach to assess these residual stresses by using wooden bilayers as a reporter system. For thin bilayers, moisture-induced stresses lead to pronounced visible flexion that can be used to identify the stress-driving parameters of the adhesive’s gelation process. These parameters depend solely on the wood/adhesive combination and are inversely determined by fitting a finite element method model on the experimentally obtained flexion state. In a subsequent step, the determined parameters are used to calculate the residual stresses in the adhesive bondline of cross-laminated timber plates, emphasizing this approach’s scale independence and general applicability to larger scale structures. All combinations of European beech and Norway spruce with the adhesives Melamine–Urea–Formaldehyde (MUF), Phenol–Resorcinol–Formaldehyde (PRF), and Polyurethane (PUR) were investigated.

Comparison of moisture susceptibility of Evotherm 3G warm mix asphalt versus hot mix asphalt

Asphalt stripping is a common form of distress caused by moisture that creates a loss of bond between the aggregate and binder. It is thought that the use of warm mix asphalt (WMA) technology could lead to increased moisture susceptibility if the free moisture present in the aggregates does not evaporate at the lower mixing temperatures. The purpose of this study is to evaluate the moisture susceptibility of WMA using Evotherm 3G on laboratory-prepared and plant-prepared mixes. The moisture damage potential was evaluated using the TSR (tensile strength ratio), the static immersion test, moisture-induced stress tester, and Hamburg wheel tracking test. Additionally, plant-prepared mixes were also assessed for TSR and rut depth. The results indicated that WMA provided adequate levels of resistance to moisture damage, reduced swelling, and improved coating. Laboratory mixes showed reduced resistance to rutting, but rut depth of plant mixes was similar to that of hot mix asphalt.

Climate impact on reinforcements in wooden members – effective hygro-expansion coefficients

ABSTRACT Wood is a hygroscopic material. The moisture content changes due to ambient climate variations e.g. according to erection and service time. The moisture content adapts first on the surface, and moisture gradient develop over the cross section and results in moisture induced stresses (MIS). MIS occur in addition to normal stresses for the load-bearing resistance and can affect reinforcements. To achieve a reliable evaluation of the safety level of reinforced timber structures, the present paper shows results from experimental test series on the load, moisture, and deformation investigation of structural glulam members reinforced with internal mechanical fasteners. Stepwise climate scenarios were applied and considered climates experienced by the structural timber member before or after reinforcement. For the estimation of the swelling and shrinkage behaviour, effective hygro-expansion coefficients have been determined. The coefficients are significantly lower than previously assumed in the standards. This enables engineers to estimate the impact on reinforcements which is not neglectable and reduces damage in a wide range of applications. The research results promote the use of wood by ensuring quality, performance, and aesthetics in timber constructions.

An experimental and finite element simulation study of moisture absorption in an ordered PVAF-reinforced thermoplastic starch composite film

A two-dimensional (2D) model was established by the finite element method to study the transient hygroscopic process and moisture-induced stress to better understand the moisture absorption microscopic process of ordered polyvinyl alcohol fiber (PVAF)-reinforced thermoplastic starch (TPS) composite films and the corresponding moisture-induced stress. The Mises stress contour of moisture distribution at five time points (36, 68, 100, 176, and 348 h) under four relative humidities (RH=57%, 75%, 84%, 98%) is demonstrated. The variation in moisture content along the two paths of width (AB) and thickness (CD) in the 2D model and the moisture-induced stress were also studied in detail. The results show that when the time t is 348 h, the saturated moisture contents along CD are 5.27, 17.22, 30.58, and 59.14%, and along AB are 5.27, 17.19, 30.57, and 59.07%. In addition, the change in moisture content, regardless of whether the path was AB or CD, mainly occurred before 176 h. The simulation results of moisture absorption are in good agreement with the experimental results. The ultimate moisture-induced stress is the largest in the fiber surroundings, which are 0.398, 1.30, 2.31, and 4.48 MPa at four RHs, respectively, and the internal moisture stress of 4.48 MPa was within the tensile strength (2–6 MPa) of PVAF/TPS (PVAF <0.89 vt%), which resulted in composite film failure. This paper provides a new way to understand the moisture absorption mechanism and explore possible methods for improving the water-resistance of TPS films.

Effect of MIST Conditioning on Moisture-Induced Damage of RAP Mixes Using Elastic Moduli and Stress–Strain Behavior

Moisture-induced damage of asphalt pavements constitutes a primary distress. To quantify the extent of moisture-induced damage efficiently, a moisture-induced stress tester (MIST) was developed. This study adopts varying stress cycles of MIST to condition the asphalt mixes without and with reclaimed asphalt pavement (RAP) to ascertain their moisture-induced damage resistivity. Hence, the control mix (0% RAP) and mixes containing 10%, 20%, 30%, and 40% RAP by weight were prepared and conditioned using 0, 1,000, 2,000, 3,500, 5,000, and 10,000 stress cycles of MIST. Thereafter, an indirect tensile (IDT) strength test was conducted on the prepared mixes. Using analytical approaches, the biaxial state of stress was defined to compute the static (ES,H) and average modulus (ES,A). Increasing stress cycles of MIST decreased the stiffness of control and RAP mixes. The compressive stress–strain curve (SSC) was plotted and utilized to compute the linearity and toughness index (TI) of control and RAP mixes. Increasing stress cycles of MIST were observed to increase the ductility of control and RAP mixes, whereas prepeak linearity was observed to reduce it. The TI increased with the increase in stress cycles of MIST. New moisture damage ratios (MDRs) were computed by utilizing ES,H and ES,A and compared with the commonly adopted tensile strength ratio (TSR). Based on such MDRs, it was concluded that RAP improves the moisture-induced damage resistivity of asphalt mixes. Statistical analysis indicated that both ES,H and ES,A have the potential to be good indicators of moisture-induced damage of control and RAP mixes.

Transverse Cracking of Concrete Base Plate in CRTS III Ballastless Track Structure: Effects of Environmental Boundary Conditions

The cast-in-place concrete base plate is a main member of the China Railway Track System (CRTS) III ballastless track structure that is prone to generating early transverse cracking. Such cracks can dramatically affect the performance and service life of the railway track structure. This study investigated the influence of temperature and moisture boundary conditions on early cracking behavior of the CRTS III base plate by using approaches of both in situ measurements and numerical modelling. In-site measurements of strain and temperature were made in four test series of CRTS III base plates under the same natural environmental condition but cured with different regimes, and a total of 96 measuring positions were monitored for up to 150 days. The results showed that the strain magnitude and distribution in the field base plate, the initial time at cracking, and the observed cracking pattern varied significantly between the different test series. In order to understand the mechanisms that create these transverse cracks and to provide guidelines for the current curing strategy during construction, the characteristics of temperature-induced and moisture-induced stresses were analyzed by using 3D numerical modelling and by considering early-age concrete creep properties, meteorological factors, and the influence from environmental boundary conditions. The calculated results revealed that early-age transverse cracking in CRTS III base plate depends more on drying shrinkage stress than temperature stress. By conducting this study, we expect to provide guidance for reducing or eliminating early cracks of CRTS III concrete base plate.

Evaluating Moisture Damage Using Impact Resonance Test

Abstract Moisture damage in asphalt mixtures has been a major cause for premature failure of asphalt pavements for decades. Although a lot of research has been done and many test methods have been developed to evaluate moisture damage in asphalt mixtures, not much research has been done on the use of nondestructive testing techniques to evaluate moisture damage in asphalt mixtures. The impact resonance (IR) test is a nondestructive test that is used to determine material properties like dynamic elastic modulus. The IR test on asphalt mixtures is done on a thin-disk specimen (150-mm diameter and 25-mm thickness). In this study, the IR test was used to assess moisture damage in asphalt mixtures by determining the resonant frequency of asphalt mixture samples in the unconditioned and moisture conditioned state. The relative reduction (ER) in dynamic elastic modulus was calculated as the ratio of the resonant frequency of conditioned and unconditioned specimens from the IR test, which was used to evaluate moisture damage. Moisture sensitivity of the asphalt mixtures was also determined by the tensile strength ratio (TSR) test. Two different moisture conditioning procedures were used for both the IR test and TSR test—modified AASHTO T 283 (Standard Method of Test for Resistance of Compacted Asphalt Mixtures to Moisture-Induced Damage) and Moisture Induced Stress Tester (MIST) conditioning. Six different mixtures from three different aggregate sources were used in this study. A good correlation was observed between TSR values from the TSR test using both conditioning procedures and the ER values from the IR test using both conditioning procedures for the asphalt mixtures used in this study. This study shows that the IR test can be used to evaluate moisture damage in asphalt mixtures. This study also explored the effects of various parameters such as support condition, impact source, and impact location on the resonant frequency from the IR test.

Using survival and atrophy to understand the effect of RAP on moisture-induced damage susceptibility of asphalt mixes

ABSTRACT Moisture-induced stress tester (MIST) has been recently developed to simulate the dynamic stresses that cause moisture damage. In the current study, asphalt mixes containing 0%, 10%, 20%, 30%, and 40% RAP were subjected to 0, 1000, 2000, 3500, 5000, and 10,000 stress cycles of MIST and IDT strength test was conducted. The test results were analysed using the concepts of survival and atrophy to propose a damage mechanism and suggest an alternative to TSR. In unconditioned state, the control mix depicted a superior survival as compared to RAP mixes with <20% RAP, and an inferior survival as compared to RAP mixes with >20% RAP. Rate of atrophy indicated that the control mix has a higher instantaneous potential to fail (2.34 MPa in unconditioned state for control mix) than RAP mixes (0.90, 1.07, 1.13 and 1.21 MPa for 10%, 20%, 30%, and 40% RAP mix, respectively, in the unconditioned state). Stiffness and peak stress carrying capacity for control mix in unconditioned state was 310.87 and 1.47 MPa, respectively, which was higher than RAP mixes. For RAP mixes, MDRs based on rate of atrophy and TSR were > 80% thereby indicating that RAP has the potential to improve the moisture-induced damage resistivity of asphalt mixes.

Numerical assessment of wood moisture content-based assignments to service classes in EC 5 and a prediction concept for moisture-induced stresses solely using relative humidity data

Moisture content (MC) fields in wood are in strong interplay with the surrounding climate, leading to dimensional changes in wooden elements as well as variation of their material behavior. In the European standard for the design of timber structures (EC5) these effects are considered by assigning wood members to service classes which are solely based on environmental conditions, but independent of the cross-sectional dimensions. Moisture-induced stresses resulting from dimensional changes are not directly considered. In this paper, we compare the EC5 assignment of service classes to an assignment based on the actual MCs, determined by simulations. Further, we present an approach to assign the service class for solid and glued laminated timber cross sections, depending on the dimensions of the cross section and based on realistic climate simulations for one location. With the proposed approach, the influence of moisture on serviceability design can be taken into account more appropriately, which is important when computing deflections and performing simulations based on 2nd order theory. In addition, a method to estimate MC distributions for larger cross sections solely based on relative humidities is proposed. With these, also moisture-induced stresses and dimensional changes can easily be considered in a static analysis.

Genome-wide Association Mapping for the Identification of SNPs Controlling Lateral Root Plasticity in Selected Rice Germplasms of the Philippines

Lateral root plasticity is a key adaptive mechanism for drought and fluctuating moisture-induced stresses in rice. Thus, understanding the genetic control of lateral root plasticity is important to enhance the climate-resilience and productivity of rice in abiotic stressed-prone environments. Genome-wide association analysis was conducted on a selected panel of traditional rice varieties (TRVs) to find single nucleotide polymorphisms (SNPs) associated with root plasticity traits under different gradients of soil moisture stress. A total of 17 SNPs, which were significantly correlated to root plasticity traits under soil moisture stress conditions, were located in six chromosomes (2, 5, 7, 9, 10, and 12). Additionally, the accessions that showed high plasticity in total lateral root length (TLRL) under severe drought were identified from among the TRVs and assumed to possess the lone SNP associated with the trait found in Chromosome 2. Specifically, the Baksalan Kawalwal accession showed an increase in L-type lateral root length under fluctuating soil moistures (SMF) (+10.31 m) and progressive drought (PDR) (+0.90 m), relative to their continuously waterlogged (CWL) counterparts under rootbox pinboard system. This may suggest the performance of the SNP in controlling the promotion of lateral roots. Furthermore, a possible candidate gene found near the SNP in Chromosome 2 is a member of PYR/PYL/RCAR-like protein family of abscisic acid (ABA) receptors, likely suggesting that plasticity in lateral root development in rice under severe drought could be regulated by ABA. Taken together, these novel root plasticity SNPs and the respective candidate genes on Chromosome 2 have potential use in developing climate-smart rice varieties.

Cold In-Place Recycling Asphalt Mixtures: Laboratory Performance and Preliminary M-E Design Analysis.

Cold in-place recycling (CIR) asphalt mixtures are an attractive eco-friendly method for rehabilitating asphalt pavement. However, the on-site CIR asphalt mixture generally has a high air void because of the moisture content during construction, and the moisture susceptibility is vital for estimating the road service life. Therefore, the main purpose of this research is to characterize the effect of moisture on the high-temperature and low-temperature performance of a CIR asphalt mixture to predict CIR pavement distress based on a mechanistic–empirical (M-E) pavement design. Moisture conditioning was simulated by the moisture-induced stress tester (MIST). The moisture susceptibility performance of the CIR asphalt mixture (pre-mist and post-mist) was estimated by a dynamic modulus test and a disk-shaped compact tension (DCT) test. In addition, the standard solvent extraction test was used to obtain the reclaimed asphalt pavement (RAP) and CIR asphalt. Asphalt binder performance, including higher temperature and medium temperature performance, was evaluated by dynamic shear rheometer (DSR) equipment and low-temperature properties were estimated by the asphalt binder cracking device (ABCD). Then the predicted pavement distresses were estimated based on the pavement M-E design method. The experimental results revealed that (1) DCT and dynamic modulus tests are sensitive to moisture conditioning. The dynamic modulus decreased by 13% to 43% at various temperatures and frequencies, and the low-temperature cracking energy decreased by 20%. (2) RAP asphalt incorporated with asphalt emulsion decreased the high-temperature rutting resistance but improved the low-temperature anti-cracking and the fatigue life. The M-E design results showed that the RAP incorporated with asphalt emulsion reduced the international roughness index (IRI) and AC bottom-up fatigue predictions, while increasing the total rutting and AC rutting predictions. The moisture damage in the CIR pavement layer also did not significantly affect the predicted distress with low traffic volume. In summary, the implementation of CIR technology in the project improved low-temperature cracking and fatigue performance in the asphalt pavement. Meanwhile, the moisture damage of the CIR asphalt mixture accelerated high-temperature rutting and low-temperature cracking, but it may be acceptable when used for low-volume roads.

Effect of MIST conditioning on the air voids and permeability of hot asphalt mixes containing reclaimed asphalt pavement

Traffic traversing on an asphalt pavement leads to the development of hydrodynamic stress. Hence, moisture-induced stress tester (MIST) was developed to simulate the phenomenon. However, MIST has the propensity to affect the air voids (Va ) and permeability (k) characteristics of the conditioned mix. In this study, an attempt has been made to understand the effect of varying stress cycles of MIST on Va and k. Furthermore, due to the advantages associated with recycled asphalt pavement (RAP) mixes, this study also considers RAP in varying proportions of 10%, 20%, 30% and 40% by weight. The results indicate that MIST conditioning affects both Va and k of asphalt mixes. RAP mixes were observed to undergo higher changes in Va and depicted higher k than control mix. It is expected that the results of the current study may prove to be significant in explaining the change in performance parameters due to MIST conditioning.

A simulating method of moisture continuous diffusion under changing temperatures and analysis of moisture-induced stresses covering moisture desorption and reflow processes for the QFN

Moisture in the atmosphere could diffuse into plastic packaging devices, which would cause high hygro-mechanical stress and vapor stress and lead irreversible damages. In this paper, an analysis method for moisture continuous diffusion under changing temperature is proposed. Considering the vapor pressure induced strain as hygro-mechanical strain, a corresponding relationship between the parameters of hygro-mechanical stress and vapor stress is built. Subsequently, the formula of moisture-induced total stress is derived according to the superposition principle. A QFN (Quad Flat No‑lead) package model with gold wires inside is established to validate the effectiveness of the method. The moisture continuous diffusion from the absorption process to the desorption one is obtained, then the dynamic variations of the hygro-mechanical stress, vapor stress and moisture-induced total stress of the QFN during the desorption process and the entire reflow process are obtained for the first time ever. The results prove that the method in this paper can be employed for the analysis of moisture diffusion and moisture-induced stress under dynamic temperature and uneven humidity distribution.